1998 ISUZU TROOPER Pin IAT sensor

6E±65 ENGINE DRIVEABILITY AND EMISSIONS
Knock Sensor Diagnosis
The Tech 2 has two data displays available for diagnosing
the knock sensor (KS) system. The two displays are
described as follows:

ªKnock Retardº indicates the number of degrees that
the spark timing is being retarded due to a knock
condition.

ªKS Noise Channelº indicates the current voltage level
being monitored on the noise channel.
DTCs P0325 and P0327 are designed to diagnose the KS
module, the knock sensor, and the related wiring. The
problems encountered with the KS system should set a
DTC. However, if no DTC was set but the KS system is
suspect because of a detonation complaint, refer to
Detonation/Spark Knock in Symptoms.
Powertrain Control Module (PCM)
Diagnosis
To read and clear diagnostic trouble codes, use a Tech 2.
IMPORTANT:Use of a Tech 2 is recommended to clear
diagnostic trouble codes from the PCM memory.
Diagnostic trouble codes can also be cleared by turning
the ignition ªOFFº and disconnecting the battery power
from the PCM for 30 seconds. Turning off the ignition and
disconnecting the battery power from the PCM will cause
all diagnostic information in the PCM memory to be
cleared. Therefore, all the diagnostic tests will have to be
re-run.
Since the PCM can have a failure which may affect only
one circuit, following the diagnostic procedures in this
section will determine which circuit has a problem and
where it is.
If a diagnostic chart indicates that the PCM connections
or the PCM is the cause of a problem, and the PCM is
replaced, but this does not correct the problem, one of the
following may be the reason:

There is a problem with the PCM terminal connections.
The terminals may have to be removed from the
connector in order to check them properly.

The problem is intermittent. This means that the
problem is not present at the time the system is being
checked. In this case, refer to the
Symptoms portion of
the manual and make a careful physical inspection of
all component and wiring associated with the affected
system.

There is a shorted solenoid, relay coil, or harness.
Solenoids and relays are turned ªONº and ªOFFº by the
PCM using internal electronic switches called drivers.
A shorted solenoid, relay coil, or harness will not
damage the PCM but will cause the solenoid or relay to
be inoperative.
Multiple PCM Information Sensor
DTCS Set
Circuit Description
The powertrain control module (PCM) monitors various
sensors to determine the engine operating conditions.
The PCM controls fuel delivery, spark advance,
transmission operation, and emission control device
operation based on the sensor inputs.The PCM provides a sensor ground to all of the sensors.
The PCM applies 5 volts through a pull-up resistor, and
determines the status of the following sensors by
monitoring the voltage present between the 5-volt supply
and the resistor:

The engine coolant temperature (ETC) sensor

The intake air temperature (IAT) sensor

The transmission fluid temperature (TFT) sensor
The PCM provides the following sensors with a 5-volt
reference and a sensor ground signal:

The exhaust gas recirculating (EGR) pintle position
sensor

The throttle position (TP) sensor

The manifold absolute pressure (MAP) sensor
The PCM monitors the separate feedback signals from
these sensors in order to determine their operating
status.
Diagnostic Aids
IMPORTANT:Be sure to inspect PCM and engine
grounds for being secure and clean.
A short to voltage in one of the sensor input circuits may
cause one or more of the following DTCs to be set:

P0108

P0113

P0118

P0123

P0560

P0712

P0406
IMPORTANT:If a sensor input circuit has been shorted
to voltage, ensure that the sensor is not damaged. A
damaged sensor will continue to indicate a high or low
voltage after the affected circuit has been repaired. If the
sensor has been damaged, replace it.
An open in the sensor ground circuit between the PCM
and the splice will cause one or more of the following
DTCs to be set:

P0108

P0113

P0118

P0123

P0712

P0406
A short to ground in the 5-volt reference A or B circuit will
cause one or more of the following DTCs to be set:

P0107

P0122
In the 5-volt reference circuit A, between the PCM and the
splice, will cause one or more of the following DTCs to be
set:

P0122
In the 5-volt reference circuit B, between the PCM and the
splice, will cause one or more of the following DTCs to be
set:

P0107
Check for the following conditions:

6E±66
ENGINE DRIVEABILITY AND EMISSIONS

Poor connection at PCM. Inspect the harness
connectors for backed-out terminals, improper mating,
broken locks, improperly formed or damage terminals,
and a poor terminal-to-wire connection.

Damaged harness. Inspect the wiring harness for
damage. If the harness is not damaged, observe an
affected sensor's displayed value on the Tech 2 with
the ignition ªONº and the engine ªOFFº while you move
the connectors and the wiring harnesses related to the
following sensors:
IAT

ECT

TP

MAP

EGR

TFT
Multiple PCM Information Sensor DTCs Set

StepActionValue(s)Ye sNo
1Was the ªOn-Board Diagnostic (OBD) System Checkº
performed?
ÐGo to Step 2
Go to OBD
System
Check
21. Turn the ignition ªOFF,º disconnect the PCM.
2. Turn the ignition ªON,º check the 5 volt reference A
circuit for the following conditions:

A poor connection at the PCM.

An open between the PCM connector and the
splice.

A short to ground.

A short to voltage.
Is there an open or short?
ÐGo to Step 3Go to Step 4
3Repair the open or short.
Is the action complete?
ÐVerify repairÐ
4Check the sensor ground circuit for the following
conditions:

A poor connection at the PCM or the affected
sensors.

An open between the PCM connector and the
affected sensors.
Is there an open or a poor connection?
ÐGo to Step 5Go to Step 6
5Repair the open or the poor connection.
Is the action complete?
ÐVerify repairÐ
6Measure the voltage between the EGR pintle position
sensor signal circuit at the PCM harness connector and
ground.
Does the voltage measure near the specified value?
0 VGo to Step 7Go to Step 12
7Measure the voltage between the MAP sensor signal
circuit at the PCM harness connector and ground.
Does the voltage measure near the specified value?
0 VGo to Step 8Go to Step 15
8Measure the voltage between the TP sensor signal
circuit at the PCM harness connector and ground.
Does the voltage measure near the specified value?
0 VGo to Step 9Go to Step 16
9Measure the voltage between the IAT sensor signal
circuit at the PCM harness connector and ground.
Does the voltage measure near the specified value?
0 VGo to Step 10Go to Step 17
10Measure the voltage between the ECT sensor signal
circuit at the PCM harness connector and ground.
Does the voltage measure near the specified value?
0 VGo to Step 11Go to Step 18

6E±67 ENGINE DRIVEABILITY AND EMISSIONS
Multiple PCM Information Sensor DTCs Set

 
StepNo Ye s Value(s) Action
111. Disconnect the EGR valve.
2. Measure the voltage between the EGR pintle
position sensor signal circuit at the PCM harness
connector and ground.
Does the voltage measure near the specified value?
0 VGo to Step 13Go to Step 18
12Measure the voltage between the TFT sensor signal
circuit at the PCM harness connector and ground.
Does the voltage measure near the specified value?
0 VGo to Step 20Go to Step 19
13Replace the EGR valve.
Is the action complete?
ÐVerify repairÐ
14Locate and repair the short to voltage in the MAP
sensor signal circuit.
Is the action complete?
ÐVerify repairÐ
15Locate and repair the short to voltage in the TP sensor
signal circuit.
Is the action complete?
ÐVerify repairÐ
16Locate and repair the short to voltage in the IAT sensor
signal circuit.
Is the action complete?
ÐVerify repairÐ
17Locate and repair the short to voltage in the ECT
sensor signal circuit.
Is the action complete?
ÐVerify repairÐ
18Locate and repair the short to voltage in the EGR pintle
position sensor signal circuit.
Is the action complete?
ÐVerify repairÐ
19Locate and repair the short to voltage in the TFT sensor
signal circuit.
Is the action complete?
ÐVerify repairÐ
20Replace the PCM.
IMPORTANT:The replacement PCM must be
programmed. Refer to
UBS 98model year Immobilizer
Workshop Manual.
Is the action complete?Ð
Go to OBD
System
Check
Ð

6E±68
ENGINE DRIVEABILITY AND EMISSIONS
Exhaust Gas Recirculation (EGR)
Diagnosis (For except EXPORT and
SOUTH AFRICA)
Pintle position error diagnosis is covered by DTC P0402,
P0404, P1404, P0405, P0406. If EGR diagnostic trouble
codes P0402, P0404, P1404, P0405, P0406 are
encountered, refer to the DTC charts.
Engine Tech 2 Data Definitions and
Ranges
A/C CLUTCH ± Tech 2 Displays ON or OFF ±
Indicates whether the PCM has commanded the A/C
clutch ON. Used in A/C system diagnostic.
A/C REQUEST Ð Tech 2 Displays YES or NO Ð
Indicates the state of the A/C request input circuit from the
HVAC controls. The PCM uses the A/C request signal to
determine whether A/C compressor operation is being
requested.
AIR/FUEL RATIO Ð Tech 2 Range 0.0-25.5 Ð
Air/fuel ratio indicates the PCM commanded value. In
closed loop, the air/fuel ratio should normally be
displayed around ª14.2-14.7.º A lower air/fuel ratio
indicates a richer commanded mixture, which may be
seen during power enrichment or TWC protection modes.
A higher air/fuel ratio indicates a leaner commanded
mixture. This can be seen during deceleration fuel mode.
BAROMETRIC PRESSURE Ð Tech 2 Range 10-105
kPa/0.00-5.00 Volts Ð
The barometric pressure reading is determined from the
MAP sensor signal monitored during key up and wide
open throttle (WOT) conditions. The barometric pressure
is used to compensate for altitude differences and is
normally displayed around ª61-104º depending on
altitude and barometric pressure.
CHECK TRANS LAMP Ð AUTO TRANSMISSION Ð
Indicates the need to check for a DTC with the Tech 2
when the lamp is flashing 0.2 seconds ON and 0.2
seconds OFF.
CMP ACT. COUNTER ± Cam Position Activity
DECEL FUEL MODE Ð Tech 2 Display ACTIVE or
INACTIVE Ð
ªACTIVEº displayed indicates that the PCM has detected
conditions appropriate to operate in deceleration fuel
mode. The PCM will command the deceleration fuel
mode when it detects a closed throttle position while the
vehicle is traveling over 20 mph. While in the deceleration
fuel delivered by entering open loop and decreasing the
injector pulse width.
DESIRED EGR POS. Ð Tech 2 Range 0%-100% Ð
Represents the EGR pintle position that the PCM is
commanding.
DESIRED IDLE Ð Tech 2 Range 0-3187 RPM Ð
The idle speed that the PCM is commanding. The PCM
will compensate for various engine loads based on engine
coolant temperature, to keep the engine at the desired
speed.ECT Ð (Engine Coolant Temperature) Tech 2
Range ±40
C to 151
C (±40
F to 304
F) Ð
The engine coolant temperature (ECT) is mounted in the
coolant stream and sends engine temperature
information to the PCM. The PCM applies 5 volts to the
ECT sensor circuit. The sensor is a thermistor which
changes internal resistance as temperature changes.
When the sensor is cold (high resistance), the PCM
monitors a high signal voltage and interprets that as a cold
engine. As the sensor warms (decreasing resistance),
the voltage signal will decrease and the PCM will interpret
the lower voltage as a warm engine.
EGR DUTY CYCLE Ð Tech 2 Range 0%-100% Ð
Represents the EGR valve driver PWM signal from the
PCM. A duty cycle of 0% indicates that no EGR flow is
being commanded; a 100% duty cycle indicates
maximum EGR flow commanded.
EGR FEEDBACK Ð Tech 2 Range 0.00-5.00 Volts Ð
Indicates the EGR pintle position sensor signal voltage
being monitored by the PCM. A low voltage indicates a
fully extended pintle (closed valve); a voltage near 5 volts
indicates a retracted pintle (open valve).
ENGINE LOAD Ð Tech 2 Range 0%-100% Ð
Engine load is calculated by the PCM from engine speed
and MAF sensor readings. Engine load should increase
with an increase in RPM or air flow.
ENGINE RUN TIME Ð Tech 2 Range
00:00:00-99:99:99 Hrs:Min:Sec Ð
Indicates the time elapsed since the engine was started.
If the engine is stopped, engine run time will be reset to
00:00:00.
ENGINE SPEED Ð Range 0-9999 RPM Ð
Engine speed is computed by the PCM from the 58X
reference input. It should remain close to desired idle
under various engine loads with engine idling.
FUEL PUMP Ð Tech 2 Displays ON or OFF Ð
Indicates the PCM commanded state of the fuel pump
relay driver circuit.
FUEL TRIM CELL Ð Tech 2 Range 0-21 Ð
The fuel trim cell is dependent upon engine speed and
MAF sensor readings. A plot of RPM vs. MAF is divided
into 22 cells. Fuel trim cell indicates which cell is currently
active.
FUEL TRIM LEARN Ð Tech 2 Displays NO or YES
Ð
When conditions are appropriate for enabling long term
fuel trim corrections, fuel trim learn will display ªYES.º
This indicates that the long term fuel trim is responding to
the short term fuel trim. If the fuel trim learn displays
ªNO,º then long term fuel trim will not respond to changes
in short term fuel trim.
HO2S BANK 1, SEN. 1 Ð Tech 2 Range 0-1132 mV
Ð
Represents the fuel control exhaust oxygen sensor
output voltage. Should fluctuate constantly within a range
between 10 mV (lean exhaust) and 1000 mV (rich
exhaust) while operating in closed loop.

6E±69 ENGINE DRIVEABILITY AND EMISSIONS
HO2S BANK2, SEN. 1ÐTech 2 Range 0-1132 mVÐ
Represents the fuel control exhaust oxygen sensor
output voltage. Should fluctuate constantly within a range
between 10mV (lean exhaust) and 1000 mV (rich
exhaust) while operating in closed loop.
HO2S BANK 1, SEN. 1ÐTech 2 Displays NOT
READY or READYÐ
Indicates the status of the exhaust oxygen sensor. The
Tech 2 will indicate that the exhaust oxygen sensor is
ready when the PCM detects a fluctuating HO2S voltage
sufficient to allow closed loop operation. This will not
occur unless the exhaust oxygen sensor is warmed up.
HO2S BANK 2, SEN. 1 Ð Tech 2 Displays NOT
READY or READY Ð
Indicates the status of the exhaust oxygen sensor. The
Tech 2 will indicate that the exhaust oxygen sensor is
ready when the PCM detects a fluctuating HO2S voltage
sufficient to allow closed loop operation. This will not
occur unless the exhaust oxygen sensor is warmed up.
HO2S WARM UP TIME BANK 1, SEN. 1/BANK 2
SEN. 1 Ð Tech 2 Range 00:00:00-99:99:99
HRS:MIN:SEC Ð
Indicates warm-up time for each HO2S. The HO2S
warm-up time is used for the HO2S heater test. The PCM
will run the heater test only after a cold start (determined
by engine coolant and intake air temperature at the time
of start-up) and only once during an ignition cycle. When
the engine is started the PCM will monitor the HO2S
voltage. When the HO2S voltage indicates a sufficiently
active sensor, the PCM looks at how much time has
elapsed since start-up. If the PCM determines that too
much time was required for the HO2S to become active,
a DTC will set. If the engine was warm when started,
HO2S warm-up will the display ª00:00:00º.
IAC POSITION Ð Tech 2 Range 0-255 Counts Ð
Displays the commanded position of the idle air control
pintle in counts. A larger number of counts means that
more air is being commanded through the idle air
passage. Idle air control should respond fairly quickly to
changes in engine load to maintain desired idle RPM.
IAT (INTAKE AIR TEMPERATURE) Ð Tech 2 Range
±40
C to 151
C (±40
F to 304
F) Ð
The PCM converts the resistance of the intake air
temperature sensor to degrees. Intake air temperature
(IAT) is used by the PCM to adjust fuel delivery and spark
timing according to incoming air density.
IGNITION 1 Ð Tech 2 Range 0-25.5 Volts Ð
This represents the system voltage measured by the
PCM at its ignition feed.
INJ. PULSE BANK 1/INJ. PULSE BANK 2 Ð Tech 2
Range 0-1000 msec. Ð
Indicates the amount of time the PCM is commanding
each injector ªONº during each engine cycle. A longer
injector pulse width will cause more fuel to be delivered.
Injector pulse width should increase with increased
engine load.KS NOISE CHANNEL (Knock Sensor) Ð
Indicates the output from the KS noise channel. There is
always some electrical noise in an engine compartment
and to avoid mistaking this as engine knock, the output
from the knock sensor is compared to the output from the
noise channel. A knock condition is not set unless the
knock sensor output is greater than the noise channel
output.
LONG TERM FUEL TRIM BANK 1/BANK 2 Ð
The long term fuel trim is derived from the short term fuel
trim values and represents a long term correction of fuel
delivery for the bank in question. A value of 0% indicates
that fuel delivery requires no compensation to maintain
the PCM commanded air/fuel ratio. A negative value
significantly below 0% indicates that the fuel system is
rich and fuel delivery is being reduced (decreased injector
pulse width). A positive value significantly greater than
0% indicates that a lean condition exists and the PCM is
compensating by adding fuel (increased injector pulse
width). Because long term fuel trim tends to follow short
term fuel trim, a value in the negative range due to
canister purge at idle should not be considered unusual.
Fuel trim values at maximum authority may indicate an
excessively rich or lean system.
LOOP STATUS Ð Tech 2 Displays OPEN or
CLOSED Ð
ªCLOSEDº indicates that the PCM is controlling fuel
delivery according to oxygen sensor voltage. In ªOPENº
the PCM ignores the oxygen sensor voltage and bases
the amount of fuel to be delivered on TP sensor, engine
coolant, and MAF sensor inputs only.
MAF Ð Tech 2 Range 0.0-512 gm/s Ð
MAF (mass air flow) is the MAF input frequency
converted to grams of air per second. This indicates the
amount of air entering the engine.
MAP Ð Tech 2 Range 10-105 kPa (0.00-4.97 Volts)
Ð
The manifold absolute pressure (MAP) sensor measures
the change in the intake manifold pressure from engine
load, EGR flow, and speed changes. As intake manifold
pressure increases, intake vacuum decreases, resulting
in a higher MAP sensor voltage and kPa reading. The
MAP sensor signal is used to monitor intake manifold
pressure changes during the EGR flow test, to update the
BARO reading, and as an enabling factor for several of
the diagnostics.
MIL Ð Tech 2 Displays ON or OFF Ð
Indicates the PCM commanded state of the malfunction
indicator lamp.
POWER ENRICHMENT Ð Tech 2 Displays ACTIVE
or INACTIVE Ð
ªACTIVEº displayed indicates that the PCM has detected
conditions appropriate to operate in power enrichment
mode. The PCM will command power enrichment mode
when a large increase in throttle position and load is
detected. While in power enrichment mode, the PCM will
increase the amount of fuel delivered by entering open
loop and increasing the injector pulse width. This is done
to prevent a possible sag or hesitation from occurring
during acceleration.

6E±251 ENGINE DRIVEABILITY AND EMISSIONS
Diagnostic Trouble Code (DTC) P1508 IAC System Low RPM
T321115
Circuit Description
The powertrain control module (PCM) controls engine
idle speed by adjusting the position of the idle air control
(IAC) motor pintle. The IAC is a bi-directional stepper
motor driven by two coils. The PCM applies current to the
IAC coils in steps (counts) to extend the IAC pintle into a
passage in the throttle body to decrease air flow. The
PCM reverses the current to retract the pintle, increasing
air flow. This method allows highly accurate control of idle
speed and quick response to changes in engine load. If
the PCM detects a condition where too low of an idle
speed is present and the PCM is unable to adjust idle
speed by increasing the IAC counts, DTC P1508 will set,
indicating a problem with the idle control system.
Conditions for Setting the DTC

No Tech 2 test is being run.

None of these DTCs are set: TP sensor, VSS, ECT,
EGR, fuel system, MAF, MAP, IAT, canister purge,
injector control or ignition control.

Barometric pressure is above 75 kPa.

Engine coolant temperature (ECT) is above 50
C
(120
F).

Engine speed is more than 100-200 RPM lower than
desired idle, based upon coolant temperature.

The engine has been running for at least 125 seconds.

Vehicle speed is less than 1 mph.

Canister purge duty cycle is above 10%.

Ignition voltage is between 9.5 volts and 16.7 volts.
The throttle is closed.

Engine speed is lower than desired idle.

All of the above conditions are met for 10 seconds.
Action Taken When the DTC Sets

The PCM will illuminate the malfunction indicator lamp
(MIL) after the second consecutive trip in which the
fault is detected.

The PCM will store conditions which were present
when the DTC was set as Freeze Frame and in the
Failure Records data.
Conditions for Clearing the MIL/DTC

DTC P1508 can be cleared by using the Tech 2 ªClear
Infoº function or by disconnecting the PCM battery
feed.
Diagnostic Aids
Check for the following conditions:

Poor connection at PCM or IAC motor ± Inspect
harness connectors for backed-out terminals,
improper mating, broken locks, improperly formed or
damaged terminals, and poor terminal-to-wire
connection.

Damaged harness ± Inspect the wiring for damage.

Restricted air intake system ± Check for a possible
collapsed air intake duct, restricted air filter element,
or foreign objects blocking the air intake system.

Throttle body ± Check for objects blocking the IAC
passage or throttle bore, excessive deposits in the IAC

6E±254
ENGINE DRIVEABILITY AND EMISSIONS
Diagnostic Trouble Code (DTC) P1509 IAC System High RPM
T321115
Circuit Description
The powertrain control module (PCM) controls engine
idle speed by adjusting the position of the idle air control
(IAC) motor pintle. The IAC is a bi-directional stepper
motor driven by two coils. The PCM applies current to the
IAC coils in steps (counts) to extend the IAC pintle into a
passage in the throttle body to decrease air flow. The
PCM reverses the current to retract the pintle, increasing
air flow. This method allows highly accurate control of idle
speed and quick response to changes in engine load. If
the PCM detect a condition where too high of an idle
speed is present and the PCM is unable to adjust idle
speed by increasing the IAC counts, DTC P1509 will set,
indicating a problem with the idle control system.
Conditions for Setting the DTC

No Tech 2 test is being run.

None of these DTCs are set: TP sensor, VSS, ECT,
EGR, fuel system, MAF, MAP, IAT, canister purge,
injector control or ignition control.

Barometric pressure is above 75 kPa.

Engine coolant temperature is above 50
C (120
F).

Engine speed is more than 100-200 RPM lower than
desired idle, based upon coolant temperature.

The engine has been running for at least 125 seconds.

Vehicle speed is less than 1 mph.

Canister purge duty cycle is above 10%.

Ignition voltage is between 9.5 volts and 16.7 volts.

Engine speed is lower than desired idle.
All of the above conditions are met for 5 seconds.
Action Taken When the DTC Sets

The PCM will illuminate the malfunction indicator lamp
(MIL) after the second consecutive trip in which the
fault is detected.

The PCM will store conditions which were present
when the DTC was set as Freeze Frame and in the
Failure Records data.
Conditions for Clearing the MIL/DTC

DTC P1509 can be cleared by using the Tech 2 ªClear
Infoº function or by disconnecting the PCM battery
feed.
Diagnostic Aids
Check for the following conditions:

Poor connection at PCM or IAC motor ± Inspect
harness connectors for backed-out terminals,
improper mating, broken locks, improperly formed or
damaged terminals, and poor terminal-to-wire
connection.

Damaged harness ± Inspect the wiring for damage.

Vacuum leak ± Check for a condition that causes a
vacuum leak, such as disconnected or damaged
hoses, leaks at the EGR valve and the EGR pipe to the
intake manifold, leaks at the throttle body, faulty or
incorrectly installed PCV valve, leaks at the intake
manifold, etc.

6E±262
ENGINE DRIVEABILITY AND EMISSIONS
Symptom Diagnosis
Preliminary Checks
Before using this section, perform the ªOn-Board
Diagnostic (OBD) System Checkº and verify all of the
following items:

The powertrain control module (PCM) and malfunction
indicator lamp (MIL) (Service Engine Soon lamp) are
operating correctly.

There are no DTC(s) stored.

Tech 2 data is within normal operating range. Refer to
Typical Scan Data Values.

Verify the customer complaint and locate the correct
symptom in the table of contents. Perform the
procedure included in the symptom chart.
Visual/Physical Check
Several of the symptom procedures call for a careful
visual/physical check. This can lead to correcting a
problem without further checks and can save valuable
time.
This check should include the following items:

PCM grounds for cleanliness, tightness and proper
location.

Vacuum hoses for splits, kinks, and proper
connections, as shown on the ªVehicle Emission
Control Informationº label. Check thoroughly for any
type of leak or restriction.

Air intake ducts for collapsed or damaged areas.

Air leaks at throttle body mounting area, mass air flow
(MAF) sensor and intake manifold sealing surfaces.

Ignition wires for cracking, hardness, and carbon
tracking.

Wiring for proper connections, pinches and cuts.
Intermittents
IMPORTANT:An intermittent problem may or may not
turn on the malfunction indicator lamp (MIL) or store a
DTC. DO NOT use the Diagnostic Trouble Code (DTC)
charts for intermittent problems. The fault must be
present to locate the problem.
Most intermittent problems are caused by faulty electrical
connections or wiring. Perform a careful visual/physical
check for the following conditions:

Poor mating of the connector halves or a terminal not
fully seated in the connector (backed out).

Improperly formed or damaged terminal.

All connector terminals in the problem circuit should be
carefully checked for proper contact tension.

Poor terminal-to-wire connection. This requires
removing the terminal from the connector body to
check.
Road test the vehicle with a J 39200 Digital Multimeter
connected to a suspected circuit. An abnormal voltage
when the malfunction occurs is a good indication that
there is a fault in the circuit being monitored.
Use Tech 2 to help detect intermittent conditions. Tech 2s
have several features that can be used to locate anintermittent condition. Use the following feature to find
intermittent faults:

Using Tech 2's ªFreeze Frameº buffer or ªFailure
Recordsº buffer can aid in locating an intermittent
condition. Review and record the information in the
freeze frame or failure record associated with the
intermittent DTC being diagnosed. The vehicle can be
driven within the conditions that were present when the
DTC originally set.
To check for loss of diagnostic code memory, disconnect
the MAP sensor and idle the engine until the MIL (Service
Engine Soon lamp) comes on. DTC P0107 should be
stored and kept in memory when the ignition is turned
ªOFF.º If not, the PCM is faulty. When this test is
completed, make sure that you clear the DTC P0107 from
memory.
An intermittent MIL (Service Engine Soon lamp) with no
stored DTC may be caused by the following:

Ignition coil shorted to ground and arcing at ignition
wires or plugs.

MIL (Service Engine Soon lamp) wire to PCM shorted
to ground.

Poor PCM grounds. Refer to the PCM wiring
diagrams.
Check for improper installation of electrical options such
as lights, cellular phones, etc. Route ignition coil wiring
away from the ignition coils. Check all wires from the
PCM to the ignition coil for poor connections.
Check for an open diode across the A/C compressor
clutch and check for other open diodes (refer to wiring
diagrams in
Electrical Diagnosis).
If problem has not been found, refer to
PCM Connector
Symptom
tables.