1998 ISUZU TROOPER check engine light

6E±89 ENGINE DRIVEABILITY AND EMISSIONS

The valve or valve seat within the fuel pressure
regulator.

The fuel injector(s).
4. Fuel pressure that drops off during acceleration,
cruise, or hard cornering may case a lean condition.
A lean condition can cause a loss of power, surging,
or misfire. A lean condition can be diagnosed using
a Tech II Tech 2. If an extremely lean condition
occurs, the oxygen sensor(s) will stop toggling. The
oxygen sensor output voltage(s) will drop below 500
mV. Also, the fuel injector pulse width will increase.
IMPORTANT:Make sure the fuel system is not
operating in the ªFuel Cut-Off Mode.º
When the engine is at idle, the manifold pressure is
low (high vacuum). This low pressure (high vacuum)
is applied to the fuel pressure regulator diaphragm.
The low pressure (high vacuum) will offset the
pressure being applied to the fuel pressure regulator
diaphragm by the spring inside the fuel pressure
regulator. When this happens, the result is lower fuel
pressure. The fuel pressure at idle will vary slightly as
the barometric pressure changes, but the fuel
pressure at idle should always be less than the fuel
pressure noted in step 2 with the engine ªOFF.º
16.Check the spark plug associated with a particular
fuel injector for fouling or saturation in order to
determine if that particular fuel injector is leaking. If
checking the spark plug associated with a particular
fuel injector for fouling or saturation does not
determine that a particular fuel injector is leaking,
use the following procedure:

Remove the fuel rail, but leave the fuel lines and
injectors connected to the fuel rail. Refer to
Fuel Rail
Assembly
in On-Vehicle Service.

Lift the fuel rail just enough to leave the fuel injector
nozzles in the fuel injector ports.
CAUTION: In order to reduce the risk of fire and
personal injury that may result from fuel spraying on
the engine, verify that the fuel rail is positioned over
the fuel injector ports and verify that the fuel injector
retaining clips are intact.

Pressurize the fuel system by connecting a 10 amp
fused jumper between B+ and the fuel pump relay
connector.

Visually and physically inspect the fuel injector
nozzles for leaks.
17.A rich condition may result from the fuel pressure
being above 376 kPa (55 psi). A rich condition may
cause a DTC P0132 or a DTC P0172 to set.
Driveability conditions associated with rich
conditions can include hard starting (followed by
black smoke) and a strong sulfur smell in the
exhaust.20.This test determines if the high fuel pressure is due
to a restricted fuel return line or if the high fuel
pressure is due to a faulty fuel pressure regulator.
21.A lean condition may result from fuel pressure
below 333 kPa (48 psi). A lean condition may
cause a DTC P0131 or a DTC P0171 to set.
Driveability conditions associated with lean
conditions can include hard starting (when the
engine is cold ), hesitation, poor driveability, lack of
power, surging , and misfiring.
22.Restricting the fuel return line causes the fuel
pressure to rise above the regulated fuel pressure.
Command the fuel pump ªONº with Tech 2. The fuel
pressure should rise above 376 kPa (55 psi) as the
fuel return line becomes partially closed.
NOTE: Do not allow the fuel pressure to exceed 414 kPa
(60 psi). Fuel pressure in excess of 414 kPa (60 psi) may
damage the fuel pressure regulator.
CAUTION: To reduce the risk of fire and personal
injury:

It is necessary to relieve fuel system pressure
before connecting a fuel pressure gauge. Refer to
Fuel Pressure Relief Procedure, below.

A small amount of fuel may be released when
disconnecting the fuel lines. Cover fuel line
fittings with a shop towel before disconnecting, to
catch any fuel that may leak out. Place the towel in
an approved container when the disconnect is
completed.
Fuel Pressure Relief Procedure
1. Remove the fuel cap.
2. Remove the fuel pump relay from the underhood
relay center.
3. Start the engine and allow it to stall.
4. Crank the engine for an additional 3 seconds.
Fuel Gauge Installation
1. Remove the shoulder fitting cap.
2. Install fuel gauge 5-8840-0378-0 to the fuel feed line
located in front of and above the right side valve train
cover.
3. Reinstall the fuel pump relay.

6E±93 ENGINE DRIVEABILITY AND EMISSIONS
Idle Air Control (IAC) System Check
Circuit Description
The powertrain control module (PCM) controls engine
idle speed with the idle air control (IAC) valve. To increase
idle speed, the PCM retracts the IAC valve pintle away
from its seat, allowing more air to bypass the throttle bore.
To decrease idle speed, it extends the IAC valve pintle
towards its seat, reducing by pass air flow. Tech 2 will
read the PCM commands to the IAC valve in counts.
Higher counts indicate more air bypass (higher idle).
Lower counts indicate less air is allowed to bypass (lower
idle).
Diagnostic Aids
A slow, unstable, or fast idle may be caused by a non-IAC
system problem that cannot be overcome by the IAC
valve. Out of control range IAC Tech 2 counts will be
above 60 if idle is too low, and zero counts if idle is too
high. The following checks should be made to repair a
non-IAC system problem:

Vacuum leak (high idle) ± If idle is too high, stop the
engine. Fully extend (low) IAC with the Tech 2. Start
the engine. If idle speed is above 800 RPM, locate and
correct the vacuum leak, including the PCV system.
Check for binding of the throttle blade or linkage.

Lean heated oxygen sensor signal (high air/fuel ratio) ±
The idle speed may be too high or too low. Engine
speed may vary up and down, and disconnecting the
IAC valve does not help. Diagnostic trouble codes
P0131, P0151, P0171, or P0174 may be set. Tech 2
oxygen (O2) voltage will be less than 100 mV (0.1 V).
Check for low regulated fuel pressure, water in fuel, or
a restricted injector.

Rich heated oxygen sensor signal (low air/fuel ratio) ±
The idle speed will be too low. Tech 2 IAC counts will
usually be above 80. The system is obviously rich and
may exhibit black smoke in the exhaust.
Tech 2 O2 voltage will be fixed at about 750 mV (0.75
V). Check for high fuel pressure, or a leaking or
sticking injector. A silicon-contaminated heated
oxygen sensor will show an O2 voltage slow to
respond on Tech 2.
Throttle body ± Remove the IAC valve and inspect the
bore for foreign material.

IAC valve electrical connections ± IAC valve
connections should be carefully checked for proper
contact.

PCV valve ± An incorrect or faulty PCV valve may
result in an incorrect idle speed. Refer to
Diagnosis,
Rough Idle, Stalling.
If intermittent poor driveability or
idle symptoms are resolved by disconnecting the IAC,
carefully recheck the connections and valve terminal
resistance, or replace the IAC.
Test Description
Number(s) below refer to the step number(s) on the
Diagnostic Chart.
1. The Tech 2 is used to extend and retract the IAC
valve. Valve movement is verified by an engine
speed change. If no change in engine speed
occurs, the valve can be resettled when removed
from the throttle body.
2. This step checks the quality of the IAC movement in
step 1. Between 700 revolutions per minute (RPM)
and about 1500 RPM, the engine speed should
change smoothly with each flash of the tester light
in both extend and retract. If the IAC valve is
retracted beyond the control range (about 1500
RPM), it may take many flashes to extend the IAC
valve before engine speed will begin to drop. This
is normal on certain engines. Fully extending the
IAC may cause engine stall. This may be normal.

6E±98
ENGINE DRIVEABILITY AND EMISSIONS
Exhaust Gas Recirculation (EGR) System Check

StepActionValue(s)Ye sNo
1Check the EGR valve for looseness.
Is the EGR valve Loose?
ÐGo to Step 2Go to Step 3
2Tighten the EGR valve.
Is the action complete?
ÐVerify repairÐ
31. Place the transmission selector in Park or Neutral.
2. Start the engine and idle until warm.
3. Using Tech 2, command EGR ª50% ON.º
Does the engine idle rough and lose RPMs?
Ð
EGR system
working
properly. No
problem
found.
Go to Step 4
41. Engine ªOFF.º
2. Ignition ªON.º
3. Using a test light to ground, check the EGR harness
between the EGR valve and the ignition feed.
Does the test light illuminate?
ÐGo to Step 6Go to Step 5
5Repair the EGR harness ignition feed.
Was the problem corrected?
ÐVerify repairGo to Step 6
61. Remove the EGR valve.
2. Visually and physically inspect the EGR valve
pintle, valve passages and adapter for excessive
deposits, obstructions or any restrictions.
Does the EGR valve have excessive deposits,
obstructions or any restrictions?
ÐGo to Step 7Go to Step 8
7Clean or replace EGR system components as
necessary.
Was the problem corrected?
ÐVerify repairGo to Step 8
81. Ground the EGR valve metal case to battery (±).
2. Using Tech 2, command EGR ªONº and observe the
EGR valve pintle for movement.
Does the EGR valve pintle move according to
command?
ÐGo to Step 9
Go to DTC
P1406 chart
91. Remove the EGR inlet and outlet pipes from the
intake and exhaust manifolds.
2. Visually and physically inspect manifold EGR ports
and EGR inlet and outlet pipes for blockage or
restriction caused by excessive deposits or other
damage.
Do the manifold EGR ports or inlet and outlet pipes
have excessive deposits, obstructions, or any
restrictions?
ÐGo to Step 10
EGR system
working
properly. No
problem
found.
10Clean or replace EGR system components as
necessary.
Is the action complete?
ÐVerify repairÐ

6E±101 ENGINE DRIVEABILITY AND EMISSIONS
PCM Diagnostic Trouble Codes
The following table lists the diagnostic trouble codes
supported by this vehicle application. If any DTCs not
listed here are displayed by a Tech 2, the Tech 2 data may
be faulty; notify the Tech 2 manufacturer of any DTCs
displayed that are not included in the following table.
A - Emission related P-code, check engine light on as
soon as a failure detected.
B - Emission related P-code, check engine light on if a
failure detected in two consecutive trips.
C - Non emission related P-code, check engine light on
if a failure detected in one trip.
D - Non emission related P-code, no check engine
light, but P-code will be set if a failure detected.
X - Do not check.

6E±106
ENGINE DRIVEABILITY AND EMISSIONS
DTC P0101 ± MAF System Performance

 
StepNo Ye s Value(s) Action
61. Ignition ªON,º engine ªOFF.º
2. Review the Freeze Frame and/or Failure Records
data for this DTC and note parameters.
3. Ignition ªOFFº for 15 seconds.
4. Start the engine and operate the vehicle within the
conditions required for this diagnostic to run, and as
close to the conditions recorded in Freeze Frame
/Failure Records possible. (Special operating
conditions that need to be met before the PCM will
run this diagnostic (where applicable) are listed in
ªConditions for Setting the DTCº).
5. Using the Tech 2, select ªDTC,º then enter the DTC
number which was set.
Does the Tech 2 indicate that this diagnostic failed this
ignition?
ÐGo to Step 7
Refer to
Diagnostic
Aids
71. Check for the following conditions:

Objects blocking the MAF sensor inlet screen;

Intake manifold vacuum leaks;

Vacuum leaks at throttle body;

Vacuum leaks EGR value flange and pipes.

Crankcase ventilation valve faulty, missing, or
incorrectly installed.
2. If a problem is found, repair as necessary.
Was a problem found?
ÐVerify repairGo toStep 8
81. Ignition ªOFF.º
2. Disconnect the MAF sensor connector.
3. Ignition ªON,º engine ªOFF.º
4. Using DVM 5-8840-0285-0, measure voltage
between the MAF sensor signal circuit and chassis
ground.
Is the voltage near the specified value?
5 VGo to Step 9Go toStep 10
9Connect a test light (5-8840-0607-0) between the MAF
sensor ignition feed and ground circuits at the MAF
sensor harness connector.
Is the test light ªON?º
ÐGo to Step 13Go toStep 12
10Is the voltage less than the specified value?4.5 VGo to Step 13Go toStep 11
111. Ignition ªOFF,º disconnect the PCM.
2. Ignition ªON,º engine ªOFF.º
3. Measure voltage between the MAF signal circuit
and ground.
Does the voltage measure near the specified value?
0 VGo to Step 13Go toStep 12
12Connect a test light (5-8840-0607-0) between the MAF
sensor ignition feed circuit and chassis ground.
Is the test light ªON?º
ÐGo to Step 13Go toStep 7
131. Check for a poor connection at the MAF sensor.
2. If a poor connection is found, replace faulty
terminal(s). Refer to
Repair Procedures in
Electrical Diagnosis (8A Cell 5).
Was a poor connection found?ÐVerify repairSolved

6E±108
ENGINE DRIVEABILITY AND EMISSIONS
Test Description
Number(s) below refer to the step number(s) on the
Diagnostic Chart.
2. This step verifies that the problem is present at idle.4. A voltage reading of less than 4 or over 5 volts at the
MAF sensor signal circuit indicates a fault in the
wiring or a poor connection.
5. This verifies that ignition feed voltage and a good
ground are available at the MAF sensor.
DTC P0102 ± MAF Sensor Circuit Low Frequency

StepActionValue(s)Ye sNo
1Was the ªOn-Board Diagnostic (OBD) System Checkº
performed?
ÐGo to Step 2
Go to OBD
System
Check
21. Start the engine.
2. With the engine idling, monitor ªMAF Frequencyº
display on the Tech 2.
Is the ªMAF Frequencyº below the specified value?
3 g/SecGo to Step 4Go to Step 5
31. Ignition ªON,º engine ªOFF.º
2. Review and record Tech 2 Failure Records data.
3. Operate the vehicle within Failure Records
conditions as noted.
4. Using a Tech 2, monitor ªDTCº info for DTC P0102.
Does the Tech 2 indicate DTC P0102 failed this
ignition?
ÐGo to Step 4
Refer to
Diagnostic
Aids
41. Ignition ªOFF.º
2. Disconnect the MAF sensor connector.
3. Ignition ªON,º engine ªOFF.º
4. Using a DVM, measure voltage between the MAF
sensor signal circuit and battery ground.
Is the voltage near the specified value?
5 VGo to Step 5Go to Step 8
5Connect a test light between the MAF sensor ignition
feed and ground circuits at the MAF sensor harness
connector.
Is the test light ªON?º
ÐGo to Step 13Go to Step 6
6Connect a test light between the MAF sensor ignition
feed circuit and battery ground.
Is the test light ªON?º
ÐGo to Step 12Go to Step 7
71. Check for a poor connection at the MAF sensor.
2. If a poor connection is found, replace the faulty
terminal(s).
Was a poor connection found?
ÐVerify repairGo to Step 11
81. Ignition ªOFF.º
2. Disconnect the MAF sensor.
3. Disconnect the PCM connector for the MAF signal
circuit.
4. Ignition ªON,º engine ªOFF.º
5. With the DVM, measure the voltage between the
MAF signal terminal at the PCM and battery ground.
Is the voltage under the specified value?
4 VGo to Step 9Go to Step 10

6E±113 ENGINE DRIVEABILITY AND EMISSIONS
and wiring harnesses related to the sensor. A change
in the display will indicate the location of the fault.
If DTC P0107 cannot be duplicated, the information
included in the Failure Records data can be useful indetermining vehicle mileage since the DTC was last set.
If it is determined that the DTC occurs intermittently,
performing the DTC P0107 Diagnostic Chart may isolate
the cause of the fault.
DTC P0107 ± MAP Sensor Circuit Low Voltage

StepActionValue(s)Ye sNo
1Was the ªOn-Board Diagnostic (OBD) System Checkº
performed?
ÐGo to Step 2
Go to OBD
System
Check
21. Ignition ªON,º engine ªOFF.º
2. With the throttle closed, observe the MAP value
displayed on the Tech 2.
Is the MAP value near the specified value?
11 kPa at sea
level
Go to Step 4Go to Step 3
31. Ignition ªON,º engine ªOFF.º
2. Review and record Tech 2 Failure Records data.
3. Operate the vehicle within Failure Records
conditions as noted.
4. Using a Tech 2, monitor ªSpecific DTCº info for DTC
P0107.
Does the Tech 2 indicate DTC P0107 failed?
ÐGo to Step 4
Refer to
Diagnostic
Aids
41. Ignition ªOFF.º
2. Disconnect the MAP sensor electrical connector.
3. Jumper the 5 volt reference ªAº circuit and the MAP
signal together at the MAP sensor harness
connector.
4. Ignition ªON.º
5. Observe the MAP value displayed on the Tech 2.
Is the MAP value near the specified value?
5 V 104 kPaGo to Step 10Go to Step 5
51. Disconnect the jumper.
2. Connect a test light between B+ and the MAP
sensor signal circuit at the MAP sensor harness
connector.
3. Observe the MAP value displayed on the Tech 2.
Is the MAP value near the specified value.
5 V 104 kPaGo to Step 6Go to Step 8
61. Ignition ªOFF.º
2. Disconnect the PCM and check the 5 volt reference
ªAº circuit for an open or short to ground.
3. If the 5 volt reference ªAº circuit is open or shorted to
ground, repair it as necessary.
Was the 5 volt reference ªAº circuit open or shorted to
ground?
ÐVerify repairGo to Step 7
7Check the 5 volt reference ªAº circuit for a poor
connection at the PCM and replace the terminal if
necessary.
Did the terminal require replacement?
ÐVerify repairGo to Step 11
81. Ignition ªOFF.º
2. Disconnect the PCM, and check the MAP signal
circuit for an open, short to ground, or short to the
sensor ground circuit.
3. If the MAP sensor signal circuit is open or shorted to
ground, repair it as necessary.
Was the MAP signal circuit open or shorted to ground?
ÐVerify repairGo to Step 9

6E±116
ENGINE DRIVEABILITY AND EMISSIONS
DTC P0108 ± MAP Sensor Circuit High Voltage

StepActionValue(s)Ye sNo
1Was the ªOn-Board Diagnostic (OBD) System Checkº
performed?
ÐGo to Step 2
Go to OBD
System
Check
21. If the engine idle is rough, unstable or incorrect,
repair the idle problem before using this chart. Refer
to
Symptoms section.
2. With the engine idling, note the MAP value on the
Tech 2.
Is the MAP reading above the specified value?
90 kPaGo to Step 4Go to Step 3
31. Ignition ªON,º engine ªOFF.º
2. Review and record Tech 2 Failure Records data.
3. Operate the vehicle within Failure Records
conditions as noted.
4. Using a Tech 2, monitor ªSpecific DTCº info for DTC
P0108.
Does the Tech 2 indicate DTC P0108 failed this
ignition?
ÐGo to Step 4
Refer to
Diagnostic
Aids
41. Ignition ªOFF.º
2. Disconnected the MAP sensor electrical connector.
3. Ignition ªON.º
4. Note the MAP sensor voltage displayed on the Tech
2.
Is the MAP sensor voltage at the specified value?
0.0 V 11 kPaGo to Step 5Go to Step 6
5Probe the sensor ground circuit with a test light to B+.
Is the test light ªON?º
ÐGo to Step 7Go to Step 9
61. Check the MAP signal circuit for a short to voltage or
a short to the 5 volt reference ªAº circuit.
2. If the MAP sensor signal circuit is shorted, repair
circuit as necessary.
Was the MAP sensor signal circuit shorted?
ÐVerify repairGo to Step 11
71. Check for a poor sensor ground terminal connection
at the MAP sensor electrical connector.
2. If a problem if found, replace the faulty terminal.
Did the terminal require replacement?
ÐVerify repairGo to Step 8
8Check for a plugged or leaking vacuum supply to the
MAP sensor.
Is the vacuum supply plugged or leaking?
ÐVerify repairGo to Step 12
91. Check for a poor sensor ground terminal connection
at the PCM.
2. If a problem is found, replace the faulty terminal.
Did the terminal require replacement?
ÐVerify repairGo to Step 10
101. Check the continuity of the MAP sensor ground
circuit.
2. If the MAP sensor ground circuit measures over 5
ohms, repair open or poor connection.
Was a condition found and corrected?
ÐVerify repairGo to Step 11