1995 JEEP YJ check engine

(7) Inspect the system ground connections at the
engine (Fig. 10). For location of system grounds, refer
to Group 8, Wiring.
(8) Verify that crankcase ventilation (CCV) fresh
air hose is firmly connected to cylinder head and air
cleaner covers (Figs. 11 or 12).
(9) Verify that vacuum hose is firmly connected to
fuel pressure regulator and manifold fitting (Figs. 13
or 14).
(10) Inspect fuel tube quick-connect fitting-to-fuel
rail connections (Fig. 15).
(11) Verify that hose connections to all ports of vac-
uum fittings on intake manifold are tight and not
leaking.
(12) Inspect accelerator cable, transmission throt-
tle cable (if equipped) and cruise control cable con-
nections (if equipped). Check their connections to the
throttle arm of throttle body for any binding or re-
strictions (Fig. 16).
(13) If equipped with vacuum brake booster, verify
that vacuum booster hose is firmly connected to fit-ting on intake manifold. Also check connection to
brake vacuum booster (Fig. 17).
(14) On XJ models equipped with: a 4.0L 6-cylin-
der engine, heavy duty cooling system and/or A/C,
Fig. 9 Generator Connector and Output Wire
ConnectionsÐTypical
Fig. 10 System Ground ConnectionsÐTypical
Fig. 11 CCV SystemÐ2.5L Engine
Fig. 12 CCV SystemÐ4.0L Engine
Fig. 13 Pressure Regulator Vacuum HoseÐ2.5L
Engine
JFUEL SYSTEM GENERAL DIAGNOSIS 14 - 37

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

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

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

DIAGNOSTIC TROUBLE CODE DESCRIPTIONSÐCONTINUED
Diagnostic
Trouble CodeDRB Scan Tool Description of Diagnostic Trouble Code
44* Battery Temp Sensor Volts out of Limit An open or shorted condition exists in the en-
gine coolant temperature sensor circuit or a
problem exists in the PCM's battery tempera-
ture voltage circuit.
46** Charging System Voltage Too High Battery voltage sense input above target
charging voltage during engine operation.
47** Charging System Voltage Too Low Battery voltage sense input below target
charging during engine operation. Also, no sig-
nificant change detected in battery voltage
during active test of generator output.
51** O2S Signal Stays Below Center (Lean) Oxygen sensor signal input indicates lean air/
fuel ratio condition during engine operation.
52** O2S Signal Stays Above Center (Rich) Oxygen sensor signal input indicates rich air/
fuel ratio condition during engine operation.
53* Internal PCM Failure PCM Internal fault condition detected.
or
PCM Failure SRI Communications PCM Internal fault condition detected.
54* No Cam Sync Signal at PCM No fuel sync (camshaft signal) detected during
engine cranking.
55* Display not shown on DRB scan tool Completion of diagnostic trouble code display
on the Malfunction Indicator Lamp (Check En-
gine Lamp).
62* PCM Failure SRI miles not stored Unsuccessful attempt to update SRI (service
reminder indicator) miles in the PCM EE-
PROM.
63* PCM Failure EEPROM Write Denied Unsuccessful attempt to write to an EEPROM
location by the PCM.
* 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 - 57

CAMSHAFT POSITION SENSOR
For removal/installation procedures, refer to Group
8D, Ignition System. See Camshaft Position Sensor.
INTAKE MANIFOLD AIR TEMPERATURE SENSOR
The intake manifold air temperature sensor is in-
stalled into the intake manifold plenum (Figs. 7 or
8).
REMOVAL
(1) Disconnect the electrical connector from the
sensor.
(2) Remove the sensor from the intake manifold.
INSTALLATION
(1) Install the sensor into the intake manifold.
Tighten the sensor to 28 Nzm (20 ft. lbs.) torque.
(2) Connect the electrical connector to the sensor.
CRANKSHAFT POSITION SENSOR
For description, operation and removal/installation
procedures, refer to Group 8D, Ignition Systems in
this manual.
ENGINE COOLANT TEMPERATURE SENSOR
The coolant temperature sensor is installed in the
thermostat housing (Fig. 9).
REMOVAL
(1) Drain cooling system until the coolant level is
below the cylinder head. Observe theWARNINGSin
Group 7, Cooling.
(2) Disconnect the coolant temperature sensor wire
connector.
(3) Remove the sensor from the thermostat hous-
ing (Fig. 9).
INSTALLATION
(1) Install coolant temperature sensor into the cyl-
inder block. Tighten to 28 Nzm (21 ft. lbs.) torque.
(2) Connect the wire connector.
(3) Fill the cooling system. Refer to Group 7, Cool-
ing System.
FUEL FILTER
Refer to the Fuel Delivery System section of this
group for removal/installation procedures.
FUEL INJECTOR
REMOVAL
(1) Remove the fuel rail. Refer to Fuel Rail Re-
moval in this section.
(2) Remove the clip(s) that retain the fuel injec-
tor(s) to the fuel rail (Figs. 10 or 11).
INSTALLATION
(1) Install the fuel injector(s) into the fuel rail as-
sembly and install retaining clip(s).
(2) If the same injector(s) is being reinstalled, in-
stall new o-ring(s).
(3) Install fuel rail. Refer to Fuel Rail Installation
in this section.
(4) Start engine and check for fuel leaks.
Fig. 7 Sensor LocationÐ2.5L Engine
Fig. 8 Sensor LocationÐ4.0L Engine
Fig. 9 Engine Coolant Temperature SensorÐTypical
14 - 60 FUEL SYSTEM COMPONENT REMOVAL/INSTALLATIONJ