sensor JAGUAR XJ6 1997 2.G User Guide

of these sensors and their corresponding
ECU-controlled relays are not contained
within EFI components, but are located
throughout the engine compartment. For
further information regarding the ECU and its
relationship to the engine electrical and
ignition system, see Chapter 6.
12 Electronic Fuel Injection
(EFI) system- check
2
1Check the earth wire connections for
tightness. Check all wiring and electrical
connectors that are related to the system.
Loose electrical connectors and poor grounds
can cause many problems that resemble
more serious malfunctions.
2Check to see that the battery is fully
charged, as the control unit and sensors
depend on an accurate supply voltage in
order to properly meter the fuel.
3Check the air filter element - a dirty or
partially blocked filter will severely impede
performance and economy (see Chapter 1).
4If a blown fuse is found, renew it and see if
it blows again. If it does, search for a shorted
wire in the harness related to the system.
5Check the air intake duct from the MAF
sensor to the intake manifold for leaks, which
will result in an excessively lean mixture. Also
check the condition of the vacuum hoses
connected to the intake manifold.
6Remove the air intake duct from the throttle
body and check for carbon and residue build-
up. If it’s dirty, clean with aerosol carburettor
cleaner (make sure the can says it’s safe for
use with oxygen sensors and catalytic
converters) and a toothbrush.
7With the engine running, place a
stethoscope against each injector, one at a
time, and listen for a clicking sound, indicating
operation (see illustration).8If there is a problem with an injector,
purchase a special injector test light (noid
light) and refit it into the injector electrical
connector (see illustration). Start the engine
and make sure that each injector connector
flashes the noid light. This will test for the
proper voltage signal to the injector.Caution:
If the engine will not start and the noid
light indicates that each injector is
receiving the proper signal, there is a good
possibility that the injector(s) is stuck open
and allowing fuel into the combustion
chamber in excessive amounts. If the spark
plugs are fouled, detach the primary (low
voltage) wires from the ignition coil, disable
the fuel pump by removing the fuel pump
relay (see Section 2), remove the spark plugs
and crank the engine over. If fuel sprays from
the spark plug holes, the engine is flooded
and the fuel must be removed from the
combustion chambers.
9With the engine OFF and the fuel injector
electrical connectors disconnected, measure
the resistance of each injector (see
illustration). Each injector should measure
about 2.0 to 3.0 ohms. If not, the injector is
probably faulty.10The remainder of the system checks
should be left to a Jaguar service department
or other qualified repair workshop, as there is
a chance that the control unit may be
damaged if not performed properly.
13 Electronic Fuel Injection
(EFI) system- component
check and renewal
3
Warning: Petrol is extremely
flammable, so take extra
precautions when you work on
any part of the fuel system. See
the Warning in Section 2.
Caution: If the stereo in your vehicle is
equipped with an anti-theft system, make
sure you have the correct activation code
before disconnecting the battery.
Throttle body
Check
1Verify that the throttle linkage operates
smoothly.
2Start the engine, detach each vacuum hose
and, using your finger, check the vacuum at
each port on the throttle body with the engine
at idle and above idle. The vacuum available
from the throttle body is ported. Raise the
engine rpm and watch as vacuum increases.
It may be necessary to use a vacuum gauge.
Refer to Chapter 2B for additional information
concerning vacuum checks.
Renewal
Warning: Wait until the engine is
completely cool before
beginning this procedure.
3Detach the cable from the negative terminal
of the battery (see the Cautionat the
beginning of this Section).
4Drain the radiator (see Chapter 1).
4•10 Fuel and exhaust systems
12.9 Using an ohmmeter, measure the
resistance across both terminals
of the injector
3261 Jaguar XJ6 12.7 Use a stethoscope or a screwdriver to determine if the
injectors are working properly - they should make a steady
clicking sound that rises and falls with engine speed changes
12.8 Refit the “noid” light into the fuel injector electrical
connector and check to see that it blinks with the engine running

5Remove the air cleaner (see Chapter 1) and
the air cleaner housing (see Section 9).
6Remove the air intake duct.
7Detach the electrical connector from the
MAF sensor (see illustration).
8Remove the clamp that retains the MAF
sensor to the air intake duct (see illustration)
and lift the MAF sensor assembly from the
engine compartment.
9Detach the throttle cable from the bellcrank
(see Section 10), then remove the bellcrank
assembly from the throttle body (see
illustration).
10Detach the kickdown cable from the
bellcrank and set the cable and brackets
aside (see Chapter 7).
11Clearly label, then detach, all vacuum and
coolant hoses from the throttle body.
12Disconnect the electrical connector from
the throttle potentiometer.
13Remove the four throttle body mounting
bolts and detach the throttle body from the
intake manifold.
14Using a soft brush and carburettor
cleaner, thoroughly clean the throttle body
casting, then blow out all passages with
compressed air.
Caution: Do not clean the throttle position
sensor with any solvents or sprays. Just
wipe it off with a clean, soft cloth.
15Refitting of the throttle body is the reverse
of removal.
16Be sure to tighten the throttle body
mounting bolts to the torque listed in this
Chapter’s Specifications.
Adjustment
17Remove the air intake duct to expose the
throttle body and butterfly valve.
18Make sure the throttle body is clean and
free of burrs, nicks or carbon build-up (see
illustration).
19Measure the clearance between the
butterfly valve (throttle plate) and the wall of
the throttle body (see illustration). It should
be 0.05 mm (0.002 inch). 20If the gap is incorrect, loosen the throttle
stop locknut (see illustration)and turn the
throttle stop screw until the correct clearance
is attained.
21Refit the air intake duct and surrounding
components.
Idle Speed Control (ISC) motor
Note:The minimum idle speed is pre-set at
the factory and should not require adjustment
under normal operating conditions; however ifthe throttle body has been replaced or you
suspect the minimum idle speed has been
tampered with (for example, if the idle speed
screw was removed from the throttle body)
have the vehicle checked by a dealer service
department or a qualified automotive repair
workshop.Check
22Start the engine and allow it to reach
normal operating temperature. Switch on the
Fuel and exhaust systems 4•11
4
13.9 Remove the bellcrank assembly bolts
(arrowed) and separate it from the
throttle body13.18 The area inside the throttle body
near the throttle plate suffers from sludge
build-up because the PCV hose vents
crankcase vapour into the intake duct
13.19 Measure clearance between the
butterfly valve and the throttle body
3261 Jaguar XJ6 13.7 Push up on the clip and remove the harness connector from
the MAF sensor
13.8 Remove the air intake duct clamp from the
MAF sensor housing
13.20 Adjust the butterfly angle by
loosening the locknut on the throttle stop
and turning the adjustment bolt

36Remove the fuel rail with the fuel injectors
attached (see illustration).
37Prise off the clips and remove the fuel
injector(s) from the fuel rail (see illustration).
38If you are replacing the injector(s), discard
the old injector. If you intend to re-use the
same injectors, renew the grommets and
O-rings (see illustrations).
39Refitting of the fuel injectors is the reverse
of removal. Apply a light film of clean engine
oil to the O-rings before refitting them.
40Tighten the fuel rail mounting bolts to the
torque listed in this Chapter’s Specifications.
Fuel pressure regulator
Check
41Refer to the fuel pump/fuel pressure
check procedure (see Section 3).
Renewal
42Relieve the fuel pressure (see Section 2)
and detach the cable from the negative
terminal of the battery (see the Cautionat the
beginning of this Section).
43Detach the vacuum hose from the
regulator.
44Remove the fuel rail and the injectors as
an assembly (see Steps 30 to 39).
45Remove the fuel line from the fuel
pressure regulator (see illustration).
46Remove the fuel pressure regulator
mounting bolts and detach the pressure
regulator from the engine.
47The remainder of refitting is the reverse of
removal. Make sure the fuel lines are secure
and there are no leaks before using the car.
Supplementary air valve
Check
48The supplementary air valve provides
additional throttle valve bypass air during cold
starting and cold running conditions below
15° F. This output actuator is controlled by the
computer (ECU) in response to informationreceived from the coolant temperature sensor,
intake air temperature sensor and other
information sensors working with the fuel
injection system.
49Check for battery voltage to the
supplementary air valve. With the engine cold,
backprobe the electrical connector using a
long pin and check for battery voltage (see
illustration). Voltage should exist.
50Because of the special tools required to
test the supplementary air valve, have it
tested by a dealer service department or other
qualified repair facility.
Renewal
51Remove the intake hoses, the mounting
screws and detach the supplementary air
valve from the engine.
52Refitting is the reverse of removal.
53Be sure to use a new gasket when refitting
the idle-up valve.
Air intake plenum
Note:The air intake plenum is removed and
installed as a complete unit with the intake
manifold. In the event of damage or leaks,
remove the air intake plenum and intake
Fuel and exhaust systems 4•13
4
3261 Jaguar XJ6 13.36 . . . and remove the fuel rail with the fuel injectors attached
13.37 Remove the fuel injector retaining clips from the fuel rail
using a small screwdriver
13.45 Disconnect the fuel pressure
regulator from the fuel return line
13.38b Pick out the old injector seal but
make sure the injector body is not
damaged in the process13.38a If you plan to refit the original
injectors, remove and discard the O-rings
and grommets and fit new ones
13.49 Check for battery voltage to the
supplementary air valve

same dimensions, amperage rating, cold
cranking rating, etc. as the original.
6Refitting is the reverse of removal.
4 Battery cables-
check and renewal
1
Caution: If the stereo in your vehicle is
equipped with an anti-theft system, make
sure you have the correct activation code
before disconnecting the battery.
1Periodically inspect the entire length of
each battery cable for damage, cracked or
burned insulation and corrosion. Poor battery
cable connections can cause starting
problems and decreased engine performance.
2Check the cable-to-terminal connections at
the ends of the cables for cracks, loose wire
strands and corrosion. The presence of white,
fluffy deposits under the insulation at the
cable terminal connection is a sign that the
cable is corroded and should be renewed.
Check the terminals for distortion, missing
mounting bolts and corrosion.
3When removing the cables, always
disconnect the negative cable first and hook it
up last or the battery may be shorted by the
tool used to loosen the cable clamps. Even if
only the positive cable is being renewed, be
sure to disconnect the negative cable from
the battery first (see Chapter 1 for further
information regarding battery cable removal).
4Disconnect the cables from the battery,
then trace each of them to their opposite ends
and detach them from the starter solenoid
and earth terminals. Note the routing of each
cable to ensure correct refitting.
5If you are replacing either or both of the old
cables, take them with you when buying new
items. It is vitally important that you replace
the cables with identical parts. Cables have
characteristics that make them easy to
identify: positive cables are usually red, larger
in cross-section and have a larger diameter
battery post clamp; earth cables are usually
black, smaller in cross-section and have a
slightly smaller diameter clamp for the
negative post.
6Clean the threads of the solenoid or earth
connection with a wire brush to remove rust
and corrosion. Apply a light coat of battery
terminal corrosion inhibitor, or petroleum jelly,
to the threads to prevent future corrosion.
7Attach the cable to the solenoid or earth
connection and tighten the mounting nut/bolt
securely.
8Before connecting a new cable to the
battery, make sure that it reaches the battery
post without having to be stretched.
9Connect the positive cable first, followed by
the negative cable.
5 Ignition system- general
information and precautions
1All models are equipped with a computerised
ignition system. The ignition system consists of
the ignition coil, the crankshaft position sensor,
the amplifier and the electronic control unit
(ECU). The ignition ECU controls the ignition
timing and advance characteristics for the
engine. The ignition timing is not adjustable,
therefore, changing the position of the distributor
will not change the timing in any way. Note:In
the event the distributor must be removed from
the engine, be sure to follow the precautions
described in Section 9 and mark the engine and
distributor with paint to ensure correct refitting. If
the distributor is not marked and Ihe crankshaft is
turned while the distributor is out of the engine,
have the distributor installed by a dealer service
department. The distributor must be installed
using a special alignment tool.
2The distributor is driven by the intermediate
shaft which also drives the power steering pump.
The crankshaft position sensor is located on the
front timing cover. It detects crank position by
pulsing an electronic signal to the ECU. This
signal is sent to the ECU to provide ignition
timing specifications.
3The computerised ignition system provides
complete control of the ignition timing by
determining the optimum timing in response to
engine speed, coolant temperature, throttle
position and vacuum pressure in the intake
manifold. These parameters are relayed to the
ECU by the crankshaft position sensor, throttle
potentiometer, coolant temperature sensor and
MAF sensor. Ignition timing is altered during
warm-up, idling and warm running conditions by
the ECU. This electronic ignition system also
consists of the ignition switch, battery, coil,
distributor, spark plug leads and spark plugs.
4Refer to a dealer parts department or car
accessory outlet for any questions concerning
the availability of the distributor parts and
assemblies. Testing the crankshaft position
sensor is covered in Chapter 6.
5When working on the ignition system, take
the following precautions:
a) Do not keep the ignition switch on for
more than 10 seconds if the engine will
not start.
b) Always connect a tachometer in
accordance with the manufacturer’s
instructions. Some tachometers may be
incompatible with this ignition system.
Consult a dealer service department
before buying a tachometer for use with
this vehicle.
c) Never allow the ignition coil terminals to
touch earth. Earthing the coil could result
in damage to the igniter and/or the
ignition coil.
d) Do not disconnect the battery when the
engine is running.
6 Ignition system- check
2
Warning: Because of the high
voltage generated by the
ignition system, extreme care
should be taken when working
on the ignition components. This not only
includes the amplifier, coil, distributor and
spark plug leads, but related components
such as connectors, tachometer and other
test equipment also.
1With the ignition switch turned to the “ON”
position, a “Battery” light or an “Oil Pressure”
light is a basic check for ignition and battery
supply to the ECU.
2Check all ignition wiring connections for
tightness, cuts, corrosion or any other signs of a
bad connection.
3Use a calibrated ignition tester to verify
adequate secondary voltage (25,000 volts) at
each spark plug (see illustration). A faulty or
poor connection at that plug could also result in a
misfire. Also, check for carbon deposits inside
the spark plug boot.
4Check for carbon tracking on the coil. If
carbon tracking is evident, renew the coil and be
sure the secondary wires related to that coil are
clean and tight. Excessive wire resistance or
faulty connections could damage the coil.
5Check for battery voltage to the ignition coil
(see illustration). If battery voltage is available,
check the ignition coil primary and secondary
resistance (see Section 8).
6Check the distributor cap for any obvious
signs of carbon tracking, corroded terminals or
cracks (see Chapter 1).
7Using an ohmmeter, check the resistance of
the spark plug leads. Each wire should measure
less than 25,000 ohms.
8Check for battery voltage to the ignition
amplifier (see Section 7). If battery voltage does
not exist, check the circuit from the ignition
switch (refer to the wiring diagrams at the end of
Chapter 12).
5•2 Engine electrical systems
6.3 To use a calibrated ignition tester
(available at most car accessory outlets),
remove a plug lead from a cylinder,
connect the spark plug boot to the tester
and clip the tester to a good earth - if there
is enough voltage to fire the plug, sparks
will be clearly visible between the
electrode tip and the tester body
3261 Jaguar XJ6

9Check for battery voltage to the Ignition ON
relay (see illustration). If battery voltage does
not exist, check the circuit from the ignition ON
relay to the battery (refer to the wiring diagrams
at the end of Chapter 12). Note:See Chapter 12
for the location of the Ignition ON relay.
10Check the operation of the crankshaft
position sensor (see Chapter 6).
11If all the checks are correct, check the
voltage signal from the computer. Using an LED
type test light, backprobe the coil power lead
(negative terminal) on the ignition coil (see
illustration). Remove the coil secondary wire
and earth the terminal to the engine. Now have
an assistant crank the engine over and observe
that the test light pulses on and off. If there is no
flashing from the test light, most likely the
computer is damaged. Have the ECU diagnosed
by a dealer service department.
12Additional checks should be performed by a
dealer service department or an automotive
repair workshop.
7 Amplifier- check and renewal
2
Warning: Because of the high
voltage generated by the
ignition system, extreme care
should be taken whenever an
operation is performed involving ignitioncomponents. This not only includes the
amplifier, coil, distributor and spark plug
leads, but related components such as
connectors, tachometer and other test
equipment also.
Note:Because of the complexity and the
special tools required to test the amplifier, the
following procedure only describes a test to
verify battery voltage is reaching the amplifier.
If the wiring harness and the relays are
working properly and battery voltage is
available to the amplifier, have the ignition
system and the ECU diagnosed by a dealer
service department.
Check
1Disconnect the amplifier electrical connector
(see illustration).
2Turn the ignition key ON (engine not
running), check for battery voltage (see
illustration) to the amplifier.
3If no battery voltage is present, check the
harness from the ignition switch to the
amplifier. Refer to the wiring diagrams at the
end of Chapter 12.
Renewal
4Disconnect the negative battery terminal.
Caution: If the stereo in your vehicle is
equipped with an anti-theft system, make
sure you have the correct activation code
before disconnecting the battery.5Remove the amplifier mounting bolts (see
illustration).
6Refitting is the reverse of removal.
8 Ignition coil-
check and renewal
2
Check
1Detach the cable from the negative terminal
of the battery.
Caution: If the stereo in your vehicle is
equipped with an anti-theft system, make
Engine electrical systems 5•3
5
6.5 Check for battery voltage to the
coil (+) terminal6.9 Check for battery voltage
to the IGN ON relay6.11 Refit the LED test light to the coil
negative (-) terminal, crank the engine over
and observe the light flash in response to
the trigger signal from the computer
7.1 Remove the clip that retains the
harness connector to the amplifier7.2 Check for battery voltage to the
ignition amplifier
7.5 Remove the amplifier mountings
screws (arrowed) and lift the unit from the
engine compartment
3261 Jaguar XJ6

model but the designations are the same.
Refer to the wiring diagrams at the end of
Chapter 12.
f) Start the engine and check the alternator
for abnormal noises (a shrieking or
squealing sound indicates a bad bushing).
g) Check the specific gravity of the battery
electrolyte. If it’s low, charge the battery
(doesn’t apply to maintenance free
batteries).
h) Make sure that the battery is fully charged
(one bad cell in a battery can cause
overcharging by the alternator).
i) Disconnect the battery cables (negative
first, then positive). Caution:If the stereo
in your vehicle is equipped with an anti-
theft system, make sure you have the
correct activation code before
disconnecting the battery. Inspect the
battery posts and the cable clamps for
corrosion. Clean them thoroughly if
necessary (see Chapter 1). Reconnect the
positive cable, then the negative cable.
2Using a voltmeter, check the battery
voltage with the engine off. It should be
approximately 12 volts (see illustration).
3Start the engine and check the battery
voltage again. It should now be approximately
13.5 to 15.1 volts.
4Turn on the headlights. The voltage should
drop and then come back up, if the charging
system is working properly.
5If the voltage reading is greater than the
specified charging voltage, renew the
alternator.
6If you have an ammeter, connect it up to the
charging system according to its maker’s
instructions. If you don’t have a professional-
type ammeter, you can also use an inductive-
type current indicator. This device is
inexpensive, readily available at car accessory
outlets and accurate enough to perform simple
amperage checks like the following test.7With the engine running at 2000 rpm, check
the reading on the ammeter with all
accessories and lights off (no load), then again
with the high-beam headlights on and the
heater blower switch turned to the HI position
(full load). Compare your readings to the
standard amperage listed in this Chapter’s
Specifications.
8If the ammeter reading is less than standard
amperage, repair or renew the alternator.
9If the alternator is working but the charging
system still does function properly, check the
operation of the load dump module (see
illustration). Have this component checked at
a dealer service department.
12 Alternator-
removal and refitting
2
1Detach the cable from the negative terminal
of the battery.
Caution: If the stereo in your vehicle is
equipped with an anti-theft system, make
sure you have the correct activation code
before disconnecting the battery.2Detach the electrical connectors from the
alternator.
3Loosen the alternator adjustment and pivot
bolts (see illustration) and detach the
drivebelt.
4Remove the adjustment and pivot bolts
(see illustration)from the alternator
adjustment bracket.
5If you are replacing the alternator, take the
old alternator with you when purchasing a
replacement unit. Make sure that the
new/rebuilt unit is identical to the old
alternator. Look at the terminals - they should
be the same in number, size and locations as
the terminals on the old alternator. Finally,
look at the identification markings - they will
be stamped in the housing or printed on a tag
or plaque affixed to the housing. Make sure
that these numbers are the same on both
alternators.
6Many new/rebuilt alternators do not have
a pulley installed, so you may have to switch
the pulley from the old unit to the new/rebuilt
one. When buying an alternator, find out the
policy regarding refitting of pulleys - some
shops will perform this service free of charge.
7Refitting is the reverse of removal.
5•6 Engine electrical systems
12.3 Loosen the lock bolt and back-off
the adjustment bolt (arrowed) to remove
the drivebelt12.4 Remove the pivot bolt and nut
3261 Jaguar XJ6 11.2 Connect the probes of a voltmeter to the battery terminals
and observe battery voltage with the engine OFF
and then with the engine running
11.9 The load dump module is located on the bulkhead
next to the MAF sensor

3261 Jaguar XJ6
6
Chapter 6
Emissions and engine control systems
EGR gas temperature sensor resistance
Temperature:
212° F . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 to 100 k-ohms
400° F . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 to 8 k-ohms
662° F . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250 to 350 ohms
Torque wrench settingNm lbf ft
Crankshaft sensor bolt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 20 Air Injection Reactor (AIR) system . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Catalytic converter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
CHECK ENGINE light . . . . . . . . . . . . . . . . . . . . . . . . . . . See Section 3
Crankcase ventilation system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Electronic control system and ECU . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Evaporative Emission Control (EVAP) system . . . . . . . . . . . . . . . . . . 6Exhaust Gas Recirculation (EGR) system . . . . . . . . . . . . . . . . . . . . . 6
Fuel tank cap gasket renewal . . . . . . . . . . . . . . . . . . . . . See Chapter 1
General information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Information sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
On Board Diagnosis (OBD) system -
description and fault code access . . . . . . . . . . . . . . . . . . . . . . . . . 3
6•1
Specifications Contents
Easy,suitable for
novice with little
experienceFairly easy,suitable
for beginner with
some experienceFairly difficult,
suitable for competent
DIY mechanic
Difficult,suitable for
experienced DIY
mechanicVery difficult,
suitable for expert DIY
or professional
Degrees of difficulty
54321
1 General information
To minimise pollution of the atmosphere
from incompletely burned and evaporating
gases and to maintain good driveability and
fuel economy, a number of emission control
systems are used on these vehicles. They
include the:
Air Injection Reactor (AIR) system
Crankcase Ventilation system
Exhaust Gas Recirculation (EGR) system
Electronic Fuel Injection (EFI) system
Evaporative Emission Control (EVAP)
system
Three-way catalytic converter (TWC)
system
The sections in this chapter include general
descriptions, checking procedures within the
scope of the home mechanic and component
renewal procedures (when possible) for each
of the systems listed above.
Before assuming an emissions control
system is malfunctioning, check the fuel and
ignition systems carefully (Chapters 4 and 5).
The diagnosis of some emission control
devices requires specialised tools, equipment
and training. If checking and servicing becometoo difficult or if a procedure is beyond the
scope of your skills, consult your dealer
service department or other repair workshop.
This doesn’t mean, however, that emission
control systems are particularly difficult to
maintain and repair. You can quickly and
easily perform many checks and do most of
the regular maintenance at home with
common tune-up and hand tools. Note:The
most frequent cause of emission problems is
simply a loose or broken electrical connector
or vacuum hose, so always check the
electrical connectors and vacuum hoses first.Pay close attention to any special
precautions outlined in this chapter. It should
be noted that the illustrations of the various
systems may not exactly match the system
installed on your vehicle because of changes
made by the manufacturer during production
or from year-to-year.
The Vehicle Emissions Control Information
(VECI) label and a vacuum hose diagram are
located under the bonnet (see illustrations).
These contain important emissions specifi-
cations and setting procedures, and a
vacuum hose schematic with emissions
1.6a The Vehicle Emissions Control
Information (VECI) label shows the types of
emission control systems installed, engine
information, etc (1992 model shown)
1.6b Typical vacuum hose routing label
(1992 model shown)

components identified. When servicing the
engine or emissions systems, the VECI label
in your particular vehicle should always be
checked for up-to-date information.
2 Electronic control system
and ECU
General description
Note: These models are susceptible to ECU
damage if water is allowed to build up in the
front cowl drain and overspill into the dash
area near the computer. Inspect and clear the
front cowl drain as a regular maintenance item
to keep the water draining properly. Remove
the duckbill-type rubber hose and inspect it
for clogging, collapsing or deterioration.
1The Lucas LH Engine Management system
controls the fuel injection system by means of
a microcomputer known as the Electronic
Control unit (ECU).
2The ECU receives signals from various
sensors which monitor changing engine
operating conditions such as intake air mass,
intake air temperature, coolant temperature,
engine rpm, acceleration/deceleration,
exhaust oxygen content, etc. These signals
are utilised by the ECU to determine the
correct injection duration.
3The system is analogous to the central
nervous system in the human body: The
sensors (nerve endings) constantly relay
signals to the ECU (brain), which processes
the data and, if necessary, sends out a
command to change the operating
parameters of the engine (body).
4Here’s a specific example of how one
portion of this system operates: An oxygen
sensor, located in the exhaust manifold,
constantly monitors the oxygen content of the
exhaust gas. If the percentage of oxygen in
the exhaust gas is incorrect, an electrical
signal is sent to the ECU. The ECU takes this
information, processes it and then sends a
command to the fuel injection system telling it
to change the air/fuel mixture. This happens in
a fraction of a second and it goes on
continuously when the engine is running. The
end result is an air/fuel mixture ratio which is
constantly maintained at a predetermined
ratio, regardless of driving conditions.
5In the event of a sensor malfunction, a
backup circuit will take over to provide
driveability until the problem is identified and
fixed.
Precautions
6Follow these steps:
a) Always disconnect the power by either
turning off the ignition switch or
disconnecting the battery terminals before
removing electrical connectors.
Warning: Later models are
equipped with airbags. To
prevent accidental deployment ofthe airbag, which could cause personal
injury, DO NOT work in the vicinity of the
steering column or instrument panel. The
manufacturer recommends that, on airbag
equipped models, the following procedure
should be left to a dealer service
department or other repair workshop
because of the special tools and techniques
required to disable the airbag system.
Caution: If the stereo in your vehicle is
equipped with an anti-theft system, make
sure you have the correct activation code
before disconnecting the battery.
b) When refitting a battery, be particularly
careful to avoid reversing the positive and
negative battery cables. Also, make sure
the ignition key is in the Off position when
connecting or disconnecting the battery.
c) Do not subject EFI components,
emissions-related components or the
ECU to severe impact during removal or
refitting.
d) Do not be careless during fault diagnosis.
Even slight terminal contact can invalidate
a testing procedure and damage one of
the numerous transistor circuits.
e) Never attempt to work on the ECU or
open the ECU cover. The ECU is
protected by a government-mandated
extended warranty that will be nullified if
you tamper with or damage the ECU.
f) If you are inspecting electronic control
system components during rainy weather,
make sure that water does not enter any
part. When washing the engine
compartment, do not spray these parts or
their electrical connectors with water.
g) These models are susceptible to ECU
damage if water is allowed to build up in
the front cowl drain and overspill into the
dash area. Inspect and clear the front
cowl drain system as a regular
maintenance item to keep the water
draining properly. Remove the duckbill
type rubber hose and inspect it for
clogging, collapsing or deterioration.
ECU removal and refitting
7Disconnect the negative cable from the
battery (see Chapter 5).
Warning: Later models are
equipped with airbags. To
prevent the accidental deploy-
ment of the airbag, which could
cause personal injury, DO NOT work in the
vicinity of the steering column or
instrument panel. The manufacturer
recommends that, on airbag equipped
models, the following procedure should be
left to a dealer service department or other
repair workshop because of the special
tools and techniques required to disable
the airbag system.
Caution: If the stereo in your vehicle is
equipped with an anti-theft system, make
sure you have the correct activation code
before disconnecting the battery.8Remove the lower instrument panel on the
passenger side under the glove compartment
(see Chapter 11).
9Remove the glove compartment from the
passenger compartment (see Chapter 11).
10Remove the screws from the ECU bracket
(see illustration).
11Lower the ECU and unplug the electrical
connectors.
12Refitting is the reverse of removal.
3 On Board Diagnosis (OBD)
system- description and fault
code access
2
Note: 1990 and 1991 models may set
Code 69 erroneously. If the battery voltage
drops sufficiently and the ignition key is
switched quickly from OFF to START, battery
voltage will be lowered and during cranking
causing a delayed park/neutral signal from the
decoder module to the ECU. Check all the
battery connections and the condition of the
battery and then check the rotary switch
adjustment in Chapter 7 to remedy this code.
General information
1The ECU contains a built-in self-diagnosis
system which detects and identifies
malfunctions occurring in the network. When
the ECU detects a problem, three things
happen: the CHECK ENGINE light comes on,
the fault is identified and a diagnostic code is
recorded and stored. The ECU stores the
failure code assigned to the specific problem
area until the diagnosis system is cancelled.
Note: 1988 and 1989 models are not
equipped with long term memory. It is
possible to access the codes but the operator
must remember to NOT turn the ignition key to
the OFF position after the CHECK ENGINE
light has been noticed. The codes will be lost
and it will be necessary to start the engine and
operate the vehicle through a complete drive
cycle to allow the fault code(s) to be set once
again. Instead of turning the ignition key to the
OFF position, simply stop at position II (key
ON but engine not running) to retain the fault
codes.
6•2 Emissions and engine control systems
3261 Jaguar XJ6
2.10 The ECU is located behind the
passenger’s side glovebox near the footrest
area. Remove the mounting screws
(arrowed) and carefully lower the ECU

2The CHECK ENGINE warning light, which is
located on the instrument panel, comes on
when the ignition switch is turned to ON and
the engine is not running. When the engine is
started, the warning light should go out. If the
light remains on, the self-diagnosis system
has detected a malfunction. Note: The
CHECK ENGINE light on early models is
displayed on the dashboard VCM panel on the
right side. Later models are equipped with a
separate CHECK ENGINE light on the left side
of the instrument cluster.Note:Not all the
codes will cause the CHECK ENGINE light to
activate. When performing any fuel or
emissions systems diagnosis, always check
for codes that may be stored but not indicated
by the CHECK ENGINE light.
Obtaining fault code output
3To obtain an output of diagnostic codes,
verify first that the battery voltage is above 11
volts, the throttle is fully closed, the
transmission is in Park, the accessory
switches are off and the engine is at normal
operating temperature.
4Turn the ignition switch to ON but don’t
start the engine (Position II). Note:On 1988
and 1989 models, remember to turn the
ignition switch to position II without turning
the key to OFF.
5Press the VCM button on the display panel
(see illustration)and observe the LED display
on the dash for the designated codes. An
asterisk next to the code indicates that there
are multiple codes stored.
6The numerical values will be displayed on
the trip computer display on the dashboard.
7If there are any malfunctions in the system,
the corresponding fault codes are displayed in
numerical order, lowest to highest.
Cancelling a diagnostic code
8After the faulty component has been
repaired/renewed, the fault code(s) stored in
computer memory must be cancelled.
a) On 1988 to 1991 vehicles, simply drive
the vehicle faster than 19 mph and the
computer will automatically erase the
stored fault code from memory.b) On 1992 to 1994 models, disconnect the
negative battery lead for 30 seconds or
more to erase the stored fault codes.
Caution: If the stereo in your vehicle is
equipped with an anti-theft system, make
sure you have the correct activation code
before disconnecting the battery.
9A stored code can also be cancelled on
early models by removing the cable from the
battery negative terminal, but other items with
memory (such as the clock and radio presets)
will also be cancelled.
10If the diagnosis code is not cancelled, it
will be stored by the ECU and appear with any
new codes in the event of future trouble.
11Should it become necessary to work on
engine components requiring removal of the
battery terminal, always check to see if a
diagnostic code has been recorded before
disconnecting the battery.
4 Information sensors
Note: Refer to Chapters 4 and 5 for additional
information on the location and the diagnostic
procedures for the output actuators (ISC
motor, air supplementary valve, distributor,
amplifier, etc.) that are not directly covered in
this section.
Coolant temperature sensor
General description
1The coolant temperature sensor is a
thermistor (a resistor which varies the value of
its voltage output in accordance with
temperature changes) which is threaded into
the thermostat housing. As the sensor
temperature DECREASES, the resistance
values will INCREASE. As the sensor
Emissions and engine control systems 6•3
6
3.5 To access the self-diagnosis system
fault codes, locate the VCM button on the
dash and with the ignition key ON (engine
not running) press it to display the codes
3261 Jaguar XJ6
Fault code chart for 1988 and 1989 models
Code System affected Probable cause
1 Oxygen sensor Open oxygen sensor circuit
2 Airflow sensor Not in operating range
3 Coolant temperature sensor Not in operating range
4 Oxygen sensor System indicates full rich
5 Throttle potentiometer/airflow sensor Low throttle potentiometer signal
with high airflow sensor signal
6 Throttle potentiometer/airflow sensor High throttle potentiometer signal
with low airflow sensor signal
7 Throttle potentiometer Idle fuel adjustment failure
8 Intake air temperature sensor Open or shorted circuit in IAT sensor
harness
Fault code chart for 1990 to 1994 models
Code System affected Probable cause
11 Idle potentiometer Not in operating range
12 Airflow sensor Not in operating range
14 Coolant temperature sensor Not in operating range
16 Air temperature sensor Not in operating range
17 Throttle potentiometer Not in operating range
18 Throttle potentiometer/airflow sensor Signal resistance low
at wide open throttle
19 Throttle potentiometer/airflow sensor Signal resistance high at idle
22 Heated oxygen sensor Open or short circuit
22 Fuel pump circuit Open or short circuit
23 Fuel supply Rich exhaust Indicated
24 Ignition amplifier circuit Open or short circuit
26 Oxygen sensor circuit Lean exhaust/vacuum leak
29 ECU Self check
33 Fuel injector circuit Open or short circuit
34 Fuel injector circuit Faulty injector indicated
37 EGR solenoid circuit Short or open circuit
39 EGR circuit Faulty system operation
44 Oxygen sensor circuit Rich or lean condition
46 Idle speed control valve - (coil 1) Open or short circuit
47 Idle speed control valve - (coil 2) Open or short circuit
48 Idle speed control valve Not within specification
68 Road speed sensor Incorrect signal voltage
69 Neutral safety switch circuit Engine cranks in Drive
(adjust or renew switch)
89 Purge control valve circuit Open or short circuit

temperature INCREASES, the resistance
values will DECREASE. A failure in this sensor
circuit should set a Code 3 (1988 and 1989)
or 13 (1990 to 1994). This code indicates a
failure in the coolant temperature sensor
circuit, so in most cases the appropriate
solution to the problem will be either repair of
a connector or wire, or renewal of the sensor.
Check
2To check the sensor, measure its resistance
value (see illustration)while it is completely
cold (60 to 80° F = 1500 to 3000 ohms). Next,
start the engine and warm it up until it reaches
operating temperature. The resistance should
be lower (180 to 200° F = 280 to 350 ohms).
3If the resistance values of the coolant
temperature sensor are correct, check the
circuit for the proper signal voltage. Turn the
ignition key ON (engine not running) and
check for reference voltage with a high-
impedance digital voltmeter (see illustration).
It should be approximately 5 volts.
Renewal
Warning: Wait until the engine is
completely cool before
beginning this procedure.
4To remove the sensor, depress the locking
tabs, unplug the electrical connector, then
carefully unscrew the sensor.
Caution: Handle the coolant sensor with
care. Damage to this sensor will affect the
operation of the entire fuel injection
system.
5Before refitting the new sensor, wrap the
threads with Teflon sealing tape to prevent
leakage and thread corrosion.
6Refitting is the reverse of removal.
Oxygen sensor
Note:An oxygen sensor splash shield is
equipped on models from VIN 664941 (mid-1990) to present. This shield prevents the self
diagnosis system from setting an intermittent
and erroneous code 44. Whenever replacing
an oxygen sensor, make sure the splash shield
is in place.
General description
7These models are equipped with a heated
oxygen sensor system. The oxygen sensor is
mounted ahead of the front catalytic converter
and monitors the exhaust gases before they
are changed. The electrical heating system
incorporated into the oxygen sensor allows for
quicker warm-up time and more efficient
oxygen content monitoring. The oxygen sensor
monitors the oxygen content of the exhaust
gas stream. The oxygen content in the exhaust
reacts with the oxygen sensor to produce a
voltage output which varies from 0.1 volts (high
oxygen, lean mixture) to 0.9 volts (low oxygen,
rich mixture). The ECU constantly monitors this
variable voltage output to determine the ratio of
oxygen to fuel in the mixture. The ECU alters
the air/fuel mixture ratio by controlling the pulse
width (open time) of the fuel injectors. A mixture
ratio of 14.7 parts air to 1 part fuel is the ideal
mixture ratio for minimising exhaust emissions,
thus allowing the catalytic converter to operate
at maximum efficiency. This ratio of 14.7 to 1 is
the one which the ECU and the oxygen sensor
attempt to maintain at all times.
8The oxygen sensor produces no voltage
when it is below its normal operating
temperature of about 600° F. During this initial
period before warm-up, the ECU operates in
open loop mode.
9If the engine reaches normal operating
temperature and/or has been running for two or
more minutes, and if the oxygen sensor is
producing a steady signal voltage below
0.45 volts at 1500 or more rpm, the ECU will set
a Code 4 (1988 and 1989) or 26 (1990 to 1994).
10When there is a problem with the oxygen
sensor or its circuit, the ECU operates in theopen loop mode - that is, it controls fuel
delivery in accordance with a programmed
default value instead of feedback information
from the oxygen sensor.
11The proper operation of the oxygen
sensor depends on four conditions:
a) Electrical - The low voltages generated by
the sensor depend upon good, clean
connections which should be checked
whenever a malfunction of the sensor is
suspected or indicated.
b) Outside air supply - The sensor is
designed to allow air circulation to the
internal portion of the sensor. Whenever
the sensor is removed and installed or
renewed, make sure the air passages are
not restricted.
c) Proper operating temperature - The ECU
will not react to the sensor signal until the
sensor reaches approximately 600° F.
This factor must be taken into
consideration when evaluating the
performance of the sensor.
d) Unleaded fuel - The use of unleaded fuel
is essential for proper operation of the
sensor. Make sure the fuel you are using
is of this type.
12In addition to observing the above
conditions, special care must be taken
whenever the sensor is serviced.
a) The oxygen sensor has a permanently
attached pigtail and electrical connector
which should not be removed from the
sensor. Damage to or removal of the
pigtail or electrical connector can
adversely affect operation of the sensor.
b) Grease, dirt and other contaminants
should be kept away from the electrical
connector and the louvered end of the
sensor.
c) Do not use cleaning solvents of any kind
on the oxygen sensor.
d) Do not drop or roughly handle the sensor.
6•4 Emissions and engine control systems
3261 Jaguar XJ6 4.2 The coolant temperature sensor is in the thermostat housing.
To check the coolant temperature sensor, use an ohmmeter to
measure the resistance between the two sensor terminals
4.3 Check for reference voltage to the electrical connector for the
coolant sensor with the ignition key ON (engine not running).
It should be approximately 5.0 volts