ECO mode JEEP CHEROKEE 1995 Service Service Manual

coolant temperature drops to 98ÉC (208ÉF). Refer to
Group 7, Cooling Systems for more information.
The relay is located in the power distribution cen-
ter (PDC) (Fig. 25).
The electric radiator cooling fan is not used on YJ
models.
SCI TRANSMITÐPCM OUTPUT
SCI Transmit is the serial data communication
transmit circuit for the DRB scan tool. The power-
train control module (PCM) transmits data to the
DRB through the SCI Transmit circuit.
SHIFT INDICATORÐPCM OUTPUT
Vehicles equipped with manual transmissions have
an Up-Shift indicator lamp. The lamp is controlled by
the powertrain control module (PCM). The lamp illu-
minates on the instrument panel to indicate when
the driver should shift to the next highest gear for
best fuel economy. The PCM will turn the lamp OFF
after 3 to 5 seconds if the shift of gears is not per-
formed. The up-shift lamp will remain off until vehi-
cle stops accelerating and is brought back to range of
up-shift lamp operation. This will also happen if ve-
hicle is shifted into fifth gear.
The indicator lamp is normally illuminated when
the ignition switch is turned on and it is turned off
when the engine is started up. With the engine run-
ning, the lamp is turned on/off depending upon en-
gine speed and load.
SPEED CONTROLÐPCM OUTPUT
Speed control operation is regulated by the power-
train control module (PCM). The PCM controls the
vacuum to the throttle actuator through the speed
control vacuum and vent solenoids. Refer to Group
8H for speed control information.
TACHOMETERÐPCM OUTPUT
The powertrain control module (PCM) supplies en-
gine rpm values to the instrument cluster tachometer
(if equipped). Refer to Group 8E for tachometer infor-
mation.
TORQUE CONVERTER CLUTCH RELAYÐPCM
OUTPUT
ALL 2.5L 4 CYL. WITH 3-SPEED AUTO. TRANS
4.0L 6 CYL. YJ MODELS WITH 3-SPEED AUTO.
TRANS
The transmission mounted torque converter clutch
(TCC) solenoid is used to control the torque con-
verter. The solenoid is controlled through the power-
train control module (PCM) and by the TCC relay.
This relay is used only on vehicles equipped with a
3-speed automatic transmission.
An electrical output signal is sent from the PCM to
the TCC relay after the PCM receives information
from the vehicle speed, MAP, throttle position and
engine coolant temperature sensors. After the TCC
relay receives this necessary information, it will send
a signal to the torque converter clutch solenoid to
control the torque converter.
On YJ models the TCC relay is located in the en-
gine compartment, on the cowl panel and near the
battery (Fig. 26). On XJ models the TCC relay is lo-
cated in the power distribution center (PDC) (Fig.
25).
AIR CLEANER
The air cleaner assembly used on all models (Figs.
27 or 28) is open to ambient air. The blend air door
and vacuum motor that was used on engines of pre-
vious model years to supply heated air, is no longer
used. The air cleaner housing contains the engine air
cleaner element.
Fig. 25 PDCÐXJ Models
Fig. 26 TCC Relay LocationÐYJ Models
JFUEL SYSTEM COMPONENT DESCRIPTION/SYSTEM OPERATION 14 - 29

The powertrain control module (PCM) monitors air
temperature in the intake manifold through the in-
take manifold air temperature sensor. The PCM ad-
justs injector pulse width and ignition timing to
compensate for intake manifold air temperature. Re-
fer to Powertrain Control Module (PCM) for more in-
formation.
For removal and installation procedures of both the
air cleaner housing and the air cleaner element, refer
to the Component Removal/Installation section of
this group
OPEN LOOP/CLOSED LOOP MODES OF
OPERATION
As input signals to the powertrain control module
(PCM) change, the PCM adjusts its response to the
output devices. For example, the PCM must calculate
different injector pulse width and ignition timing for
idle than it does for wide open throttle (WOT). There
are several different modes of operation that deter-
mine how the PCM responds to the various input sig-
nals.
MODES
²Open Loop
²Closed Loop
During Open Loop modes, the powertrain control
module (PCM) receives input signals and respondsonly according to preset PCM programming. Input
from the oxygen (O2S) sensor is not monitored dur-
ing Open Loop modes.
During Closed Loop modes, the PCM will monitor
the oxygen (O2S) sensor input. This input indicates
to the PCM whether or not the calculated injector
pulse width results in the ideal air-fuel ratio. This
ratio is 14.7 parts air-to-1 part fuel. By monitoring
the exhaust oxygen content through the O2S sensor,
the PCM can fine tune the injector pulse width. This
is done to achieve optimum fuel economy combined
with low emission engine performance.
The fuel injection system has the following modes
of operation:
²Ignition switch ON
²Engine start-up (crank)
²Engine warm-up
²Idle
²Cruise
²Acceleration
²Deceleration
²Wide open throttle (WOT)
²Ignition switch OFF
The ignition switch On, engine start-up (crank), en-
gine warm-up, acceleration, deceleration and wide
open throttle modes are Open Loop modes. The idle
and cruise modes, (with the engine at operating tem-
perature) are Closed Loop modes.IGNITION SWITCH (KEY-ON) MODE
This is an Open Loop mode. When the fuel system
is activated by the ignition switch, the following ac-
tions occur:
Fig. 27 Air CleanerÐXJ ModelsÐTypical
Fig. 28 Air CleanerÐYJ ModelsÐTypical
14 - 30 FUEL SYSTEM COMPONENT DESCRIPTION/SYSTEM OPERATIONJ

²The powertrain control module (PCM) pre-posi-
tions the idle air control (IAC) motor.
²The PCM determines atmospheric air pressure
from the MAP sensor input to determine basic fuel
strategy.
²The PCM monitors the engine coolant temperature
sensor input. The PCM modifies fuel strategy based
on this input.
²Intake manifold air temperature sensor input is
monitored
²Throttle position sensor (TPS) is monitored
²The auto shutdown (ASD) relay is energized by the
PCM for approximately three seconds.
²The fuel pump is energized through the fuel pump
relay by the PCM. The fuel pump will operate for ap-
proximately three seconds unless the engine is oper-
ating or the starter motor is engaged
²The O2S sensor heater element is energized
through the fuel pump relay. The O2S sensor input is
not used by the PCM to calibrate air-fuel ratio dur-
ing this mode of operation.
²The up-shift indicator lamp is illuminated (manual
transmission only).
ENGINE START-UP MODE
This is an Open Loop mode. The following actions
occur when the starter motor is engaged.
The powertrain control module (PCM) receives in-
puts from:
²Battery voltage
²Engine coolant temperature sensor
²Crankshaft position sensor
²Intake manifold air temperature sensor
²Manifold absolute pressure (MAP) sensor
²Throttle position sensor (TPS)
²Starter motor relay
²Camshaft position sensor signal
The PCM monitors the crankshaft position sensor.
If the PCM does not receive a crankshaft position
sensor signal within 3 seconds of cranking the en-
gine, it will shut down the fuel injection system.
The fuel pump is activated by the PCM through
the fuel pump relay.
Voltage is applied to the fuel injectors with the
PCM. The PCM will then control the injection se-
quence and injector pulse width by turning the
ground circuit to each individual injector on and off.
The PCM determines the proper ignition timing ac-
cording to input received from the crankshaft posi-
tion sensor.
ENGINE WARM-UP MODE
This is an Open Loop mode. During engine warm-
up, the powertrain control module (PCM) receives in-
puts from:
²Battery voltage
²Crankshaft position sensor
²Engine coolant temperature sensor²Intake manifold air temperature sensor
²Manifold absolute pressure (MAP) sensor
²Throttle position sensor (TPS)
²Camshaft position sensor signal (in the distribu-
tor)
²Park/neutral switch (gear indicator signalÐauto.
trans. only)
²Air conditioning select signal (if equipped)
²Air conditioning request signal (if equipped)
Based on these inputs the following occurs:
²Voltage is applied to the fuel injectors with the
powertrain control module (PCM). The PCM will
then control the injection sequence and injector pulse
width by turning the ground circuit to each individ-
ual injector on and off.
²The PCM adjusts engine idle speed through the
idle air control (IAC) motor and adjusts ignition tim-
ing.
²The PCM operates the A/C compressor clutch
through the clutch relay. This is done if A/C has been
selected by the vehicle operator and requested by the
A/C thermostat.
²If the vehicle has a manual transmission, the up-
shift lamp is operated by the PCM.
²When engine has reached operating temperature,
the PCM will begin monitoring O2S sensor input.
The system will then leave the warm-up mode and go
into closed loop operation.
IDLE MODE
When the engine is at operating temperature, this
is a Closed Loop mode. At idle speed, the powertrain
control module (PCM) receives inputs from:
²Air conditioning select signal (if equipped)
²Air conditioning request signal (if equipped)
²Battery voltage
²Crankshaft position sensor
²Engine coolant temperature sensor
²Intake manifold air temperature sensor
²Manifold absolute pressure (MAP) sensor
²Throttle position sensor (TPS)
²Camshaft position sensor signal (in the distribu-
tor)
²Battery voltage
²Park/neutral switch (gear indicator signalÐauto.
trans. only)
²Oxygen sensor
Based on these inputs, the following occurs:
²Voltage is applied to the fuel injectors with the
powertrain control module (PCM). The PCM will
then control injection sequence and injector pulse
width by turning the ground circuit to each individ-
ual injector on and off.
²The PCM monitors the O2S sensor input and ad-
justs air-fuel ratio by varying injector pulse width. It
also adjusts engine idle speed through the idle air
control (IAC) motor.
JFUEL SYSTEM COMPONENT DESCRIPTION/SYSTEM OPERATION 14 - 31

²The PCM adjusts ignition timing by increasing
and decreasing spark advance.
²The PCM operates the A/C compressor clutch
through the clutch relay. This happens if A/C has
been selected by the vehicle operator and requested
by the A/C thermostat.
The optional Extended Idle Switch is used to raise
the engine idle speed to approximately 1000 rpm.
This is when the shifter is in either the Park or Neu-
tral position. A rocker-type 2-wire switch (extended
idle switch) is mounted to the instrument panel. This
switch will supply a ground circuit to the powertrain
control module (PCM).The switch is available
only with 4.0L engine when supplied with the
optional police package.
CRUISE MODE
When the engine is at operating temperature, this
is a Closed Loop mode. At cruising speed, the power-
train control module (PCM) receives inputs from:
²Air conditioning select signal (if equipped)
²Air conditioning request signal (if equipped)
²Battery voltage
²Engine coolant temperature sensor
²Crankshaft position sensor
²Intake manifold air temperature sensor
²Manifold absolute pressure (MAP) sensor
²Throttle position sensor (TPS)
²Camshaft position sensor signal (in the distribu-
tor)
²Park/neutral switch (gear indicator signalÐauto.
trans. only)
²Oxygen (O2S) sensor
Based on these inputs, the following occurs:
²Voltage is applied to the fuel injectors with the
PCM. The PCM will then adjust the injector pulse
width by turning the ground circuit to each individ-
ual injector on and off.
²The PCM monitors the O2S sensor input and ad-
justs air-fuel ratio. It also adjusts engine idle speed
through the idle air control (IAC) motor.
²The PCM adjusts ignition timing by turning the
ground path to the coil on and off.
²The PCM operates the A/C compressor clutch
through the clutch relay. This happens if A/C has
been selected by the vehicle operator and requested
by the A/C thermostat.
ACCELERATION MODE
This is an Open Loop mode. The powertrain control
module (PCM) recognizes an abrupt increase in
throttle position or MAP pressure as a demand for
increased engine output and vehicle acceleration. The
PCM increases injector pulse width in response to in-
creased throttle opening.
DECELERATION MODE
When the engine is at operating temperature, this
is an Open Loop mode. During hard deceleration, the
powertrain control module (PCM) receives the follow-
ing inputs.
²Air conditioning select signal (if equipped)
²Air conditioning request signal (if equipped)
²Battery voltage
²Engine coolant temperature sensor
²Crankshaft position sensor
²Intake manifold air temperature sensor
²Manifold absolute pressure (MAP) sensor
²Throttle position sensor (TPS)
²Camshaft position sensor signal (in the distribu-
tor)
²Park/neutral switch (gear indicator signalÐauto.
trans. only)
If the vehicle is under hard deceleration with the
proper rpm and closed throttle conditions, the PCM
will ignore the oxygen sensor input signal. The PCM
will enter a fuel cut-off strategy in which it will not
supply battery voltage to the injectors. If a hard de-
celeration does not exist, the PCM will determine the
proper injector pulse width and continue injection.
Based on the above inputs, the PCM will adjust en-
gine idle speed through the idle air control (IAC) mo-
tor.
The PCM adjusts ignition timing by turning the
ground path to the coil on and off.
The PCM opens the ground circuit to the A/C
clutch relay to disengage the A/C compressor clutch.
This is done until the vehicle is no longer under de-
celeration (if the A/C system is operating).
WIDE OPEN THROTTLE MODE
This is an Open Loop mode. During wide open
throttle operation, the powertrain control module
(PCM) receives the following inputs.
²Battery voltage
²Crankshaft position sensor
²Engine coolant temperature sensor
²Intake manifold air temperature sensor
²Manifold absolute pressure (MAP) sensor
²Throttle position sensor (TPS)
²Camshaft position sensor signal (in the distribu-
tor)
During wide open throttle conditions, the following
occurs:
²Voltage is applied to the fuel injectors with the
powertrain control module (PCM). The PCM will
then control the injection sequence and injector pulse
width by turning the ground circuit to each individ-
ual injector on and off. The PCM ignores the oxygen
sensor input signal and provides a predetermined
amount of additional fuel. This is done by adjusting
injector pulse width.
²The PCM adjusts ignition timing by turning the
ground path to the coil on and off.
14 - 32 FUEL SYSTEM COMPONENT DESCRIPTION/SYSTEM OPERATIONJ

²The PCM opens the ground circuit to the A/C
clutch relay to disengage the A/C compressor clutch.
This will be done for approximately 15 seconds (if the
air conditioning system is operating).
If the vehicle has a manual transmission, the up-
shift lamp is operated by the PCM.
IGNITION SWITCH OFF MODE
When ignition switch is turned to OFF position,
the PCM stops operating the injectors, ignition coil,
ASD relay and fuel pump relay.
THROTTLE BODY
Filtered air from the air cleaner enters the intake
manifold through the throttle body (Fig. 29). Fuel
does not enter the intake manifold through the throt-
tle body. Fuel is sprayed into the manifold by the fuel
injectors. The throttle body is mounted on the intake
manifold. It contains an air control passage (Fig. 30)
controlled by an Idle Air Control (IAC) motor. The air
control passage is used to supply air for idle condi-
tions. A throttle valve (plate) is used to supply air for
above idle conditions.
The throttle position sensor (TPS) and idle air con-
trol (IAC) motor are attached to the throttle body.
The accelerator pedal cable, speed control cable and
transmission control cable (when equipped) are con-
nected to the throttle arm.
A (factory adjusted) set screw is used to mechani-
cally limit the position of the throttle body throttle
plate.Never attempt to adjust the engine idle
speed using this screw.All idle speed functions are
controlled by the PCM.
FUEL RAIL
The fuel rail supplies fuel to the injectors and is
mounted to the intake manifold (Fig. 31). The fuel
pressure regulator is attached to the rail and the fuel
pressure test port is integral with the rail. The fuel
rail is not repairable.
FUEL PRESSURE REGULATOR
The fuel pressure regulator (Fig. 32) is a mechani-
cal device that is not controlled by the powertrain
control module (PCM).
Fig. 29 Throttle BodyÐTypical
Fig. 30 Idle Air Control Passage
Fig. 31 Fuel RailÐTypical
Fig. 32 Fuel Pressure RegulatorÐTypical
JFUEL SYSTEM COMPONENT DESCRIPTION/SYSTEM OPERATION 14 - 33

MULTI-PORT FUEL INJECTION (MFI)ÐGENERAL DIAGNOSIS
INDEX
page page
Automatic Shutdown (ASD) Relay Testing....... 46
Camshaft Position Sensor Test............... 46
Crankshaft Position Sensor Test.............. 47
Diagnostic Trouble Code (DTC)............... 54
DRB Scan Tool........................... 54
Engine Coolant Temperature Sensor Test....... 46
Extended Idle Switch Test................... 48
Fuel Injector Test......................... 51
Fuel Pump Relay Testing................... 47
Fuel System Pressure Test.................. 51
General Information....................... 35
Idle Air Control Motor Test................... 49
Intake Manifold Air Temperature Sensor Test..... 46Manifold Absolute Pressure (Map) Sensor Test . . . 47
On-Board Diagnostics (OBD)................. 51
Oxygen Sensor (O2S) Heating Element Test..... 48
Pcm System Schematics.................... 41
Powertrain Control Module (PCM) 60-Way
Connector............................. 40
RelaysÐOperation/Testing.................. 50
Starter Motor Relay Test.................... 51
Throttle Position Sensor (TPS) Test............ 48
Torque Converter Clutch Relay Test............ 48
Vehicle Speed Sensor Test.................. 48
Visual Inspection.......................... 35
GENERAL INFORMATION
All 2.5L 4-cylinder and 4.0L 6-cylinder engines are
equipped with sequential Multi-Port Fuel Injection
(MFI). The MFI system provides precise air/fuel ra-
tios for all driving conditions.
VISUAL INSPECTION
A visual inspection for loose, disconnected, or incor-
rectly routed wires and hoses should be made. This
should be done before attempting to diagnose or ser-
vice the fuel injection system. A visual check will
help spot these faults and save unnecessary test and
diagnostic time. A thorough visual inspection will in-
clude the following checks:
(1) Verify that the 60-way connector is fully in-
serted into the connector of the powertrain control
module (PCM) (Figs. 1 or 2). Verify that the connec-
tor mounting bolt is tightened to 4 Nzm (35 in. lbs.)
torque.(2) Inspect the battery cable connections. Be sure
they are clean and tight.
(3) Inspect fuel pump relay and air conditioning
compressor clutch relay (if equipped). Inspect ASD
relay and radiator fan relay (if equipped) connec-
tions. Inspect starter motor relay connections. In-
spect relays for signs of physical damage and
corrosion. The relays are installed in the power dis-
tribution center (PDC) (Figs. 3 or 4).
(4) Inspect ignition coil connections. Verify that coil
secondary cable is firmly connected to coil (Figs. 5 or
6).
(5) Verify that distributor cap is correctly attached
to distributor. Be sure that spark plug cables are
firmly connected to the distributor cap and the spark
plugs in their correct firing order. Be sure that coil
cable is firmly connected to distributor cap and coil.
Be sure that camshaft position sensor wire connector
is firmly connected to harness connector (Figs. 7 or
8). Inspect spark plug condition. Refer to Group 8D,
Fig. 1 PCMÐYJ Models
Fig. 2 PCMÐXJ Models
JFUEL SYSTEM GENERAL DIAGNOSIS 14 - 35

(8) Disconnect jumper wires from relay and 12 Volt
power source.
If continuity or resistance tests did not pass, re-
place relay. If tests passed, refer to Group 8W, Wiring
Diagrams for additional circuit information. Also re-
fer to the appropriate Powertrain Diagnostic Proce-
dures manual for operation of the DRB scan tool.
STARTER MOTOR RELAY TEST
Refer to Group 8A, Battery/Starting/Charging/Sys-
tem Diagnostics, for starter motor relay testing.
FUEL INJECTOR TEST
To perform a complete test of the fuel injectors and
their circuitry, refer to DRB scan tool and appropri-
ate Powertrain Diagnostics Procedures manual. To
test the injector only, refer to the following:
Disconnect the injector wire connector from the in-
jector. Place an ohmmeter on the injector terminals.
Resistance reading should be approximately 14.5
ohms61.2 ohms at 20ÉC (68ÉF). Proceed to the fol-
lowing Injector Diagnosis chart.When performing
the following tests from the chart, do not leave
electrical current applied to the injector for
longer than five seconds. Damage to injector
coil or internal injector seals could result.
FUEL SYSTEM PRESSURE TEST
Refer to the Fuel Delivery System section of this
group. See Fuel System Pressure Test.
ON-BOARD DIAGNOSTICS (OBD)
The powertrain control module (PCM) has been
programmed to monitor many different circuits of the
fuel injection system. If a problem is sensed in a
monitored circuit often enough to indicate an actual
problem, a Diagnostic Trouble Code (DTC) is stored.
The DTC will be stored in the PCM memory for even-
tual display to the service technician. If the problem
is repaired or ceases to exist, the PCM cancels the
DTC after 51 engine starts.Certain criteria must be met for a diagnostic trou-
ble code (DTC) to be entered into PCM memory. The
criteria may be a specific range of engine rpm, engine
temperature and/or input voltage to the PCM.
It is possible that a DTC for a monitored circuit
may not be entered into memory even though a mal-
function has occurred. This may happen because one
of the DTC criteria for the circuit has not been met.
Example: assume that one of the criteria for the
MAP sensor circuit is that the engine must be oper-
ating between 750 and 2000 rpm to be monitored for
a DTC. If the MAP sensor output circuit shorts to
ground when the engine rpm is above 2400 rpm, a 0
volt input will be seen by the PCM. A DTC will not
be entered into memory because the condition does
not occur within the specified rpm range.
A DTC indicates that the powertrain control mod-
ule (PCM) has recognized an abnormal signal in a
circuit or the system. A DTC may indicate the result
of a failure, but never identify the failed component
directly.
There are several operating conditions that the
PCM does not monitor and set a DTC for. Refer to
the following Monitored Circuits and Non-Monitored
Circuits in this section.
MONITORED CIRCUITS
The powertrain control module (PCM) can detect
certain problems in the fuel injection system.
Open or Shorted Circuit- The PCM can deter-
mine if sensor output (which is the input to PCM) is
within proper range. It also determines if the circuit
is open or shorted.
Output Device Current Flow- The PCM senses
whether the output devices are hooked up.
If there is a problem with the circuit, the PCM
senses whether the circuit is open, shorted to ground
(-), or shorted to (+) voltage.
Oxygen Sensor- The PCM can determine if the
oxygen sensor is switching between rich and lean.
This is, once the system has entered Closed Loop. Re-
fer to Open Loop/Closed Loop Modes Of Operation in
the Component Description/System Operation section
for an explanation of Closed (or Open) Loop opera-
tion.
NON-MONITORED CIRCUITS
The PCM does not monitor the following circuits,
systems or conditions that could have malfunctions
that result in driveability problems. A Diagnostic
Trouble Code (DTC) may not be displayed for these
conditions.
Fuel Pressure:Fuel pressure is controlled by the
vacuum assisted fuel pressure regulator. The PCM
cannot detect a clogged fuel pump inlet filter, clogged
in-line fuel filter, or a pinched fuel supply or return
Fig. 44 Fuel Injector Internal ComponentsÐTypical
JFUEL SYSTEM GENERAL DIAGNOSIS 14 - 51

line. However, these could result in a rich or lean
condition causing an oxygen sensor DTC to be stored
in the PCM.
Secondary Ignition Circuit:The PCM cannot
detect an inoperative ignition coil, fouled or worn
spark plugs, ignition cross firing, or open circuited
spark plug cables.
Engine Timing:The PCM cannot detect an incor-
rectly indexed timing chain, camshaft sprocket or
crankshaft sprocket. The PCM also cannot detect an
incorrectly indexed distributor. However, these could
result in a rich or lean condition causing an oxygen
sensor DTC to be stored in the PCM.
Cylinder Compression:The PCM cannot detect
uneven, low, or high engine cylinder compression.
Exhaust System:The PCM cannot detect a
plugged, restricted or leaking exhaust system.
Fuel Injector Malfunctions:The PCM cannot de-
termine if the fuel injector is clogged, or the wrong
injector is installed. However, these could result in a
rich or lean condition causing an oxygen sensor DTC
to be stored in the PCM.
Excessive Oil Consumption:Although the PCM
monitors exhaust stream oxygen content through ox-
ygen sensor (closed loop), it cannot determine exces-
sive oil consumption.
Throttle Body Air Flow:The PCM cannot detect
a clogged or restricted air cleaner inlet or air cleaner
element.
Evaporative System:The PCM will not detect a
restricted, plugged or loaded EVAP canister.
Vacuum Assist:Leaks or restrictions in the vac-
uum circuits of vacuum assisted engine control sys-
tem devices are not monitored by the PCM. However,
a vacuum leak at the MAP sensor will be monitored
and a diagnostic trouble code (DTC) will be gener-
ated by the PCM.
Powertrain Control Module (PCM) System
Ground:The PCM cannot determine a poor system
ground. However, a DTC may be generated as a re-
sult of this condition.
Powertrain Control Module (PCM) Connector
Engagement:The PCM cannot determine spread or
damaged connector pins. However, a DTC may be
generated as a result of this condition.
HIGH AND LOW LIMITS
The powertrain control module (PCM) compares in-
put signal voltages from each input device. It will es-
tablish high and low limits that are programmed into
it for that device. If the input voltage is not within
specifications and other Diagnostic Trouble Code
(DTC) criteria are met, a DTC will be stored in mem-
ory. Other DTC criteria might include engine rpm
limits or input voltages from other sensors or
switches. The other inputs might have to be sensed
by the PCM when it senses a high or low input volt-
age from the control system device in question.
ACCESSING DIAGNOSTIC TROUBLE CODES
A stored diagnostic trouble code (DTC) can be dis-
played by cycling the ignition key On-Off-On-Off-On
within three seconds and observing the malfunction
indicator lamp. This lamp is displayed on the instru-
ment panel as the CHECK ENGINE lamp (Figs. 45
or 46).
They can also be displayed through the use of the
Diagnostic Readout Box (DRB) scan tool. The DRB
scan tool connects to the data link connector in the
engine compartment (Figs. 47 or 48). For operation of
the DRB, refer to the appropriate Powertrain Diag-
nostic Procedures service manual.
Fig. 45 Check Engine LampÐXJ ModelsÐTypical
Fig. 46 Check Engine LampÐYJ ModelsÐTypical
JFUEL SYSTEM GENERAL DIAGNOSIS 14 - 53

EXAMPLES:
²If the lamp (Figs. 45 or 46) flashes 1 time, pauses
and flashes 2 more times, a flashing Diagnostic Trou-
ble Code (DTC) number 12 is indicated. If this code is
observed, it is indicating that the battery has been
disconnected within the last 50 key-on cycles. It
could also indicate that battery voltage has been dis-
connected to the PCM. In either case, other DTC's
may have been erased.
²If the lamp flashes 4 times, pauses and flashes 1
more time, a flashing Diagnostic Trouble Code (DTC)
number 41 is indicated.
²If the lamp flashes 4 times, pauses and flashes 6
more times, a flashing Diagnostic Trouble Code
(DTC) number 46 is indicated.
After any stored DTC information has been ob-
served, the display will end with a flashing DTC
number 55. This will indicate the end of all stored in-
formation.
Refer to the Diagnostic Trouble Code (DTC) charts
for DTC identification.If the problem is repaired or ceases to exist, the
Powertrain Control Module (PCM) cancels the DTC
after 51 engine starts.
Diagnostic Trouble Codes indicate the results of a
failure, but never identify the failed component di-
rectly.
The circuits of the data link connector are shown in
(Fig. 49).
ERASING TROUBLE CODES
After the problem has been repaired, use the DRB
scan tool to erase a Diagnostic Trouble Code (DTC).
Refer to the appropriate Powertrain Diagnostic Pro-
cedures service manual for operation of the DRB
scan tool.
DRB SCAN TOOL
For operation of the DRB scan tool, refer to the ap-
propriate Powertrain Diagnostic Procedures service
manual.
DIAGNOSTIC TROUBLE CODE (DTC)
On the following pages, a list of diagnostic trouble
codes is provided for the 2.5L 4-cylinder and 4.0L
6-cylinder engines. A DTC indicates that the power-
train control module (PCM) has recognized an abnor-
mal signal in a circuit or the system. A DTC may
indicate the result of a failure, but never identify the
failed component directly.
Fig. 47 Data Link ConnectorÐYJ ModelsÐTypical
Fig. 48 Data Link ConnectorÐXJ ModelsÐTypical
Fig. 49 Data Link Connector Schematic
14 - 54 FUEL SYSTEM GENERAL DIAGNOSISJ

INTAKE MANIFOLD
Refer to Group 11, Exhaust System and Intake
Manifold for removal/installation procedures.
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR
The MAP sensor is located on the dash panel near
the rear of the engine cylinder head (valve) cover
(Fig. 15).
REMOVAL
(1) Disconnect the MAP sensor electrical connector
(Fig. 15).
(2) Disconnect the MAP sensor vacuum supply
hose (Fig. 15).
(3) Remove the MAP sensor mounting bolts and re-
move MAP sensor.
INSTALLATION
(1) Install MAP sensor to dash panel and secure
with mounting bolts.
(2) Install the MAP sensor vacuum supply hose.
(3) Connect the MAP sensor electrical connector.
OXYGEN (O2S) SENSOR
The O2S sensor is installed in the exhaust down
pipe just below the exhaust manifold flange (Fig. 16).
REMOVAL
WARNING: THE EXHAUST MANIFOLD BECOMES
VERY HOT DURING ENGINE OPERATION. ALLOW
ENGINE TO COOL BEFORE REMOVING OXYGEN
SENSOR.
(1) Raise and support the vehicle.
(2) Separate the electrical connectors.
(3) Remove the O2S sensor from the exhaust man-
ifold. Snap-On oxygen sensor wrench (number YA
8875) may be used for removal and installation.
INSTALLATION
Threads of new factory oxygen sensors are coated
with anti-seize compound to aid in removal.
(1) Install the O2S sensor into the exhaust mani-
fold and tighten to 30 Nzm (22 ft. lbs.) torque.
(2) Connect the O2S sensor wire connector to the
main harness.
(3) Lower the vehicle.
PARK NEUTRAL SWITCH
Refer to Group 21, Transmissions for park neutral
switch service.
POWER STEERING PRESSURE SWITCHÐ2.5L
ENGINE ONLY
The power steering pressure switch is installed in
the power steering high-pressure hose (Figs. 17 or
18).
REMOVAL
(1) Disconnect the electrical connector from the
power steering pressure switch.
Fig. 15 MAP SensorÐTypical
Fig. 16 Oxygen SensorÐTypical
Fig. 17 Power Steering Pressure SwitchÐYJ Models
JFUEL SYSTEM COMPONENT REMOVAL/INSTALLATION 14 - 63