engine JEEP XJ 1995 Service And Repair Manual

Fig. 32 System SchematicÐXJ Models with 4.0L Engine
JFUEL SYSTEM GENERAL DIAGNOSIS 14 - 45

AUTOMATIC SHUTDOWN (ASD) RELAY TESTING
To perform a complete test of the ASD relay and its
circuitry, refer to the DRB scan tool and appropriate
Powertrain Diagnostics Procedures manual. To test
the relay only, refer to RelaysÐOperation/Testing in
this section of the group.
CAMSHAFT POSITION SENSOR TEST
Refer to Group 8D, Ignition Systems, for Camshaft
Position Sensor testing.
ENGINE COOLANT TEMPERATURE SENSOR TEST
To perform a complete test of the engine coolant
temperature sensor and its circuitry, refer to DRB
scan tool and appropriate Powertrain Diagnostics
Procedures manual. To test the sensor only, refer to
the following:
Disconnect wire harness connector from engine
coolant temperature sensor (Fig. 33).
Test the resistance of the sensor with a high input
impedance (digital) volt-ohmmeter. The resistance
should be less than 1000 ohms with the engine at its
correct operating temperature. Refer to the Coolant
Temperature Sensor/Manifold Air Temperature Sen-
sor resistance chart. Replace the sensor if it is not
within the range of resistance specified in the chart.
Test continuity of the wire harness. Do this be-
tween the Powertrain Control Module (PCM) wire
harness connector terminal-2 and the sensor connec-
tor terminal. Also test continuity of wire harness ter-
minal-4 to the sensor connector terminal. Repair the
wire harness if an open circuit is indicated.
INTAKE MANIFOLD AIR TEMPERATURE SENSOR
TEST
To perform a complete test of the sensor and its cir-
cuitry, refer to DRB scan tool and appropriate Pow-ertrain Diagnostics Procedures manual. To test the
sensor only, refer to the following:
Disconnect the wire harness connector from the in-
take manifold air temperature sensor (Figs. 34 or
35).
Test the resistance of the sensor with an input im-
pedance (digital) volt-ohmmeter. The resistance
should be less than 4000 ohms with the engine at op-
erating temperature. The longer the engine idles, the
warmer the intake manifold temperature will be-
come. Refer to the Coolant Temperature Sensor/Man-
ifold Air Temperature Sensor resistance chart.
Replace the sensor if it is not within the range of re-
sistance specified in the chart.
Fig. 33 Engine Coolant Temperature SensorÐ
Typical
SENSOR RESISTANCE (OHMS)ÐCOOLANT
TEMPERATURE SENSOR/MANIFOLD AIR
TEMPERATURE
Fig. 34 Air Temperature SensorÐ2.5L Engine
14 - 46 FUEL SYSTEM GENERAL DIAGNOSISJ

Test the resistance of the wire harness. Do this be-
tween the powertrain control module (PCM) wire
harness connector terminal-2 and the sensor connec-
tor terminal. Also test terminal-4 to the sensor con-
nector terminal. Repair the wire harness as
necessary if the resistance is greater than 1 ohm.
FUEL PUMP RELAY TESTING
For testing this relay, refer to RelaysÐOperation/
Testing in this section of the group.
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR
TEST
To perform a complete test of the MAP sensor and
its circuitry, refer to DRB scan tool and appropriate
Powertrain Diagnostics Procedures manual. To test
the sensor only, refer to the following:
Inspect the MAP sensor vacuum hose connections
at the throttle body and sensor. Repair as necessary.
CAUTION: When testing, do not remove the electri-
cal connector from MAP sensor (Fig. 36). Be sure
that the MAP sensor harness wires are not dam-
aged by the test meter probes.
Test the MAP sensor output voltage at the MAP
sensor connector between terminals A and B (as
marked on the sensor body) (Fig. 37). With the igni-
tion switch ON and the engine OFF, output voltage
should be 4-to-5 volts. The voltage should drop to 1.5-
to-2.1 volts with a neutral-hot idle speed condition.
Test the powertrain control module (PCM) (termi-
nal-5) for the same voltage described above to verify
the wire harness condition. Repair as necessary.
Test MAP sensor supply voltage at sensor connec-
tor between terminals A and C (Fig. 37) with the ig-
nition ON and engine OFF. The voltage should be
approximately 5 volts (60.5V). Five volts (60.5V)should also be at terminal-6 of the PCM wire harness
connector. Repair or replace the wire harness as nec-
essary.
Test the MAP sensor ground circuit at sensor con-
nector terminal-A (Fig. 37) and PCM connector termi-
nal-4. Repair the wire harness if necessary.
Test the MAP sensor ground circuit at the PCM
connector between terminal-4 and terminal-11 with
an ohmmeter. If the ohmmeter indicates an open cir-
cuit, inspect for a defective sensor ground connection.
Refer to Group 8W, Wiring for location of engine
grounds. If the ground connection is good, replace the
PCM. If terminal-4 has a short circuit to 12 volts,
correct this condition before replacing the PCM.
CRANKSHAFT POSITION SENSOR TEST
Refer to Group 8D, Ignition Systems for test proce-
dures.
Fig. 35 Air Temperature SensorÐ4.0L EngineFig. 36 MAP SensorÐTypical
Fig. 37 MAP Sensor Connector TerminalsÐTypical
JFUEL SYSTEM GENERAL DIAGNOSIS 14 - 47

EXTENDED IDLE SWITCH TEST
OPTIONAL POLICE PACKAGE ONLY
OPERATION
The extended idle switch is used to raise the en-
gine idle speed to approximately 1000 rpm when the
shifter is in either the Park or Neutral position. A
rocker-type 2-wire switch (extended idle switch) is
mounted to the instrument panel.This switch is
available only with 4.0L engine when supplied
with the optional police package.
TESTING
The extended idle switch will control a ground cir-
cuit going to the powertrain control module (PCM).
When a ground signal (through this switch) has been
received at pin number 10 in the PCM, engine idle
speed will increase.
Bring the engine to normal operating temperature
and turn the extended idle switch to the ON position.
Engine speed should now increase to approximately
1000 rpm when the shifter is in either the Park or
Neutral position. If engine speed does not increase,
apply a good ground to pin number 10 at the PCM
using a small paper clip. Be careful not to damage
the wiring with the paper clip. If the engine speed
now increases, it can be assumed that the PCM is
functioning correctly. Check the instrument panel
mounted switch for a closed ground circuit when in
the ON position. If the engine speed will not increase
after applying a ground to pin number 10, replace
the PCM. Refer to Group 8W, Wiring Diagrams for
circuit and wiring information.
THROTTLE POSITION SENSOR (TPS) TEST
To perform a complete test of the sensor and its cir-
cuitry, refer to DRB scan tool and appropriate Pow-
ertrain Diagnostics Procedures manual. To test the
sensor only, refer to the following:
The throttle position sensor (TPS) can be tested
with a digital voltmeter. The center terminal of the
TPS is the output terminal (Figs. 38 or 39).
With the ignition key in the ON position, back-
probe the TPS connector. Check the TPS output volt-
age at the center terminal wire of the connector.
Check this at idle (throttle plate closed) and at wide
open throttle (WOT). At idle, TPS output voltage
should must be greater than 200 millivolts. At wide
open throttle, TPS output voltage must be less than
4.8 volts. The output voltage should increase gradu-
ally as the throttle plate is slowly opened from idle to
WOT.
TORQUE CONVERTER CLUTCH RELAY TEST
To test the relay only, refer to RelaysÐOperation/
Testing in this section of the group. To test the
torque converter clutch circuit and related compo-nents, refer to the appropriate Powertrain Diagnostic
Procedures manual for operation of the DRB scan
tool.
VEHICLE SPEED SENSOR TEST
To perform a complete test of the sensor and its cir-
cuitry, refer to DRB scan tool and appropriate Pow-
ertrain Diagnostics Procedures manual.
OXYGEN SENSOR (O2S) HEATING ELEMENT TEST
To perform a complete test of the O2S sensor (Fig.
40) and its circuitry, refer to DRB scan tool and ap-
propriate Powertrain Diagnostics Procedures manual.
To test the sensor only, refer to the following:
The oxygen sensor heating element can be tested
with an ohmmeter as follows:
With the sensor at room temperature 25 degrees C
(77 degrees F), disconnect the O2S sensor connector.
Connect the ohmmeter test leads across the white
wire terminals of the sensor connector. Resistance
should be between 5 and 7 ohms. Replace the sensor
if the ohmmeter displays an infinity (open) reading.
Fig. 38 TPS TestingÐ2.5L Engine
Fig. 39 TPS TestingÐ4.0L Engine
14 - 48 FUEL SYSTEM GENERAL DIAGNOSISJ

IDLE AIR CONTROL MOTOR TEST
Idle air control (IAC) motor operation can be tested
using special exerciser tool number 7558 (Fig. 41).
CAUTION: Proper safety precautions must be taken
when testing the idle air control motor:
²Set the parking brake and block the drive wheels
²Route all tester cables away from the cooling fans,
drive belt, pulleys and exhaust components
²Provide proper ventilation while operating the en-
gine
²Always return the engine idle speed to normal be-
fore disconnecting the exerciser tool
(1) With the ignition OFF, disconnect the IAC mo-
tor wire connector at throttle body (Fig. 41).
(2) Plug the exerciser tool number 7558 harness
connector into the IAC motor.
(3) Connect the red clip of exerciser tool 7558 to
battery positive terminal. Connect the black clip to
negative battery terminal. The red light on the exer-
ciser tool will flash when the tool is properly con-
nected.(4) Start engine.
When the switch on the tool is in the HIGH or
LOW position, the light on the tool will flash. This
indicates that voltage pulses are being sent to the
IAC stepper motor.
(5) Move the switch to the HIGH position. The en-
gine speed should increase. Move the switch to the
LOW position. The engine speed should decrease.
(a) If the engine speed changes while using the
exerciser tool, the IAC motor is functioning prop-
erly. Disconnect the exerciser tool and connect the
IAC motor wire connector to the stepper motor.
(b) If the engine speed does not change, turn the
ignition OFF and proceed to step (6). Do not dis-
connect exerciser tool from the IAC motor.
(6) Remove the IAC motor from the throttle body.
Do not remove IAC motor housing from throttle body.
CAUTION: When checking IAC motor operation with
the motor removed from the throttle body, do not
extend the pintle (Fig. 42) more than 6.35 mm (.250
in). If the pintle is extended more than this amount,
it may separate from the IAC motor. The IAC motor
must be replaced if the pintle separates from the
motor.
(7) With the ignition OFF, cycle the exerciser tool
switch between the HIGH and LOW positions. Ob-
serve the pintle. The pintle should move in-and-out
of the motor.
(a) If the pintle does not move, replace the idle
air control motor. Start the engine and test the re-
placement motor operation as described in step (5).
(b) If the pintle operates properly, check the idle
air control motor bore in the throttle body bore for
blockage and clean as necessary. Reinstall the idle
air control motor and retest. If blockage is not
found, refer to the DRB scan tool and the appropri-
ate Powertrain Diagnostics Procedures service
manual.
Fig. 40 Oxygen SensorÐTypical
Fig. 41 IAC Motor TestingÐTypical
Fig. 42 Idle Air Control (IAC) Motor Pintle
JFUEL SYSTEM GENERAL DIAGNOSIS 14 - 49

(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

DIAGNOSTIC TROUBLE CODE DESCRIPTIONS
Diagnostic
Trouble CodeDRB Scan Tool Description of Diagnostic Trouble Code
11* No Crank Reference Signal at PCM No crank reference signal detected during en-
gine cranking.
12* Battery Disconnect Direct battery input to PCM was disconnected
within the last 50 Key-on cycles.
13** No Change in MAP From Start to Run No difference recognized between the engine
MAP reading and the barometric (atmospheric)
pressure reading at start-up.
14** MAP Sensor Voltage Too Low MAP sensor input below minimum acceptable
voltage.
or
MAP Sensor Voltage Too High MAP sensor input above maximum acceptable
voltage.
15** No Vehicle Speed Sensor Signal No vehicle distance (speed) sensor signal de-
tected during road load conditions.
17* Engine is Cold Too Long Engine coolant temperature remains below
normal operating temperatures during vehicle
travel (thermostat).
21** O2S Stays at Center Neither rich or lean condition detected from
the oxygen sensor input.
or
O2S Shorted to Voltage Oxygen sensor input voltage maintained above
the normal operating range.
22** ECT Sensor Voltage Too High Engine coolant temperature sensor input
above maximum acceptable voltage.
or
ECT Sensor Voltage Too Low Engine coolant temperature sensor input below
minimum acceptable voltage.
23** Intake Air Temp Sensor Voltage Low Intake manifold air temperature sensor input
below the minimum acceptable voltage.
or
Intake Air Temp Sensor Voltage High Intake manifold air temperature sensor input
above the maximum acceptable voltage.
24** Throttle Position Sensor Voltage High Throttle position sensor input above the maxi-
mum acceptable voltage.
or
Throttle Position Sensor Voltage Low Throttle position sensor input below the mini-
mum acceptable voltage.
* Check Engine Lamp will not illuminate at all times if this Diagnostic Trouble Code was recorded. Cycle Ignition key
as described in manual and observe code flashed by Check Engine lamp.
** Check Engine Lamp will illuminate during engine operation if this Diagnostic Trouble Code was recorded.
JFUEL SYSTEM GENERAL DIAGNOSIS 14 - 55

DIAGNOSTIC TROUBLE CODE DESCRIPTIONSÐCONTINUED
Diagnostic
Trouble CodeDRB Scan Tool Description of Diagnostic Trouble Code
25** Idle Air Control Motor Circuits A shorted condition detected in one or more of
the idle air control motor circuits.
27* Injector #1 Control Circuit Injector #1 output driver does not respond
properly to the control signal.
or
Injector #2 Control Circuit Injector #2 output driver does not respond
properly to the control signal.
or
Injector #3 Control Circuit Injector #3 output driver does not respond
properly to the control signal.
or
Injector #4 Control Circuit Injector #4 output driver does not respond
properly to the control signal.
or
Injector #5 Control Circuit Injector #5 output driver does not respond
properly to the control signal.
or
Injector #6 Control Circuit Injector #6 output driver does not respond
properly to the control signal.
33* A/C Clutch Relay Circuit An open or shorted condition detected in the
A/C clutch relay circuit.
34* Speed Control Solenoid Circuits An open or shorted condition detected in the
Speed Control vacuum or vent solenoid cir-
cuits.
or
Speed Control Switch Always Low Speed Control switch input below the mini-
mum acceptable voltage.
or
Speed Control Switch Always High Speed Control switch input above the maxi-
mum acceptable voltage.
35*
(XJ Only)Rad Fan Control Relay Circuits An open or shorted condition detected in the
radiator fan relay circuit.
41** Generator Field Not Switching Properly An open or shorted condition detected in the
generator field control circuit.
42* Auto Shutdown Relay Control Circuit An open or shorted condition detected in the
auto shutdown relay circuit.
* Check Engine Lamp will not illuminate at all times if this Diagnostic Trouble Code was recorded. Cycle Ignition key
as described in manual and observe code flashed by Check Engine lamp.
** Check Engine Lamp will illuminate during engine operation if this Diagnostic Trouble Code was recorded.
14 - 56 FUEL SYSTEM GENERAL DIAGNOSISJ