electrical ISUZU TROOPER 1998 Service Service Manual

6E±77 ENGINE DRIVEABILITY AND EMISSIONS
Malfunction Indicator Lamp (MIL) ªONº Steady
D06RW00007
Circuit description
The malfunction indicator lamp (MIL) should always be
illuminated and steady with ignition ªONº and the engine
stopped. Ignition feed voltage is supplied directly to the
MIL indicator. The powertrain control module (PCM)
turns the MIL ªONº by grounding the MIL driver circuit.
The MIL should not remain ªONº with the engine running
and no DTC(s) set. A steady MIL with the engine running
and no DTC(s) suggests a short to ground in the MIL
driver circuit.
Diagnostic Aids
An intermittent may be caused by a poor connection,
rubbed-through wire insulation, or a wire broken inside
the insulation. Check for the following items:

Poor connection or damaged harness ± Inspect the
PCM harness and connectors for improper mating,
broken locks, improperly formed or damaged
terminals, poor terminal-to-wire connection, and
damaged harness.
Test Description
Number(s) below refer to the step number(s) on the
Diagnostic Chart.
2. If the MIL does not remain ªONº when the PCM is
disconnected, the MIL driver wiring is not faulty.
3. If the MIL driver circuit is OK, the instrument panel
cluster is faulty.
6. This vehicle is equipped with a PCM which utilizes
an electrically erasable programmable read only
memory (EEPROM). When the PCM is replaced,
the new PCM must be programmed. Refer to
UBS
98 model year Immobilizer Workshop Manual.

6E±81 ENGINE DRIVEABILITY AND EMISSIONS
Engine Cranks But Will Not Run

StepActionValue(s)Ye sNo
1Was the ªOn-Board Diagnostic (OBD) System Checkº
performed?
ÐGo to Step 2
Go to OBD
System
Check
2Check the 15 A ignition coil fuse, the 15 A engine fuse,
and the 30 A PCM fuse.
Was a fuse blown?
ÐGo to Step 3Go to Step 4
3Check for a short to ground and replace the fuse.
Is the action complete?
ÐVerify repairÐ
41. Ignition ªOFF,º install a fuel pressure gauge at the
test fitting on the fuel supply line in the engine
compartment. (Use a shop cloth to absorb any fuel
leakage while making the connection.)
2. Ignition ªON,º observe the fuel pressure.
Is the fuel pressure within the specified values, and
does it hold steady?
285-376 kPa
(43-55 psi)
Go to Step 6Go to Step 5
5Is any fuel pressure indicated?
Ð
Go to Fuel
System
Electrical TestGo to Fuel
System
Diagnosis
6Install an injector switch box to the injector test
connector, and attempt to operate the injector.
Did the fuel pressure drop when the injector is
operated?
ÐGo to Step 7Go to Step 12
7Install an injector test light at the #2 cylinder injector
harness connector.
Does the light blink when the engine is cranked?
ÐGo to Step 8Go to Step 18
81. Ignition ªON.º
2. While the coil connectors are disconnected, touch
each coil connector's ignition feed terminal with a
grounded test light (the ignition feed wire is black
with orange tracer).
Did the test light illuminate?
ÐGo to Step 10Go to Step 9
9Repair the open ignition feed circuit.
Is the action complete?
ÐVerify repairÐ
10While the coil connectors are disconnected, touch
each connector's secondary ground terminal with a
test light to B+. (The ground wires are black.)
Did the test light illuminate at each coil connector?
ÐGo to Step 12Go to Step 11
11Repair the open secondary ground circuit.
Is the action complete?
ÐVerify repairÐ
121. Test the fuel for contamination.
2. If a problem is found, clean the fuel system and
correct the contaminated fuel condition as
necessary. Replace the fuel filter and replace any
injectors that are not delivering fuel (see Injector
Balance Test).
Was a problem found?
ÐVerify repairGo to Step 13

6E±85 ENGINE DRIVEABILITY AND EMISSIONS
Fuel System Electrical Test
D06RW101
Circuit Description
When the ignition switch is first turned ªON,º the
powertrain control module (PCM) energizes the fuel
pump relay which applies power to the in-tank fuel pump.
The fuel pump relay will remain ªONº as long as the
engine is running or cranking and the PCM is receiving
58X crankshaft position pulses. If no 58X crankshaft
position pulses are present, the PCM de-energizes the
fuel pump relay within 2 seconds after the ignition is
turned ªONº or the engine is stopped.
The fuel pump delivers fuel to the fuel rail and injectors,
then to the fuel pressure regulator. The fuel pressure
regulator controls fuel pressure by allowing excess fuel to
be returned to the fuel tank. With the engine stopped and
ignition ªON,º the fuel pump can be turned ªONº by using a
command by Tech 2.
Diagnostic Aids
An intermittent may be caused by a poor connection,
rubbed-through wire insulation, or a wire broken inside
the insulation. Check for the following items:

Poor connection or damaged harness ± Inspect the
PCM harness and connectors for improper mating,
broken locks, improperly formed or damaged
terminals, poor terminal-to-wire connection, and
damaged harness.
Test Description
Number(s) below refer to the step number(s) on the
Diagnostic Chart.
2. If the fuel pump is operating but incorrect pressure is
noted, the fuel pump wiring is OK and the ªFuel
System Pressure Testº chart should be used for
diagnosis.

6E±86
ENGINE DRIVEABILITY AND EMISSIONS
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.
Fuel System Electrical Test

StepActionValue(s)Ye sNo
1Was the ªOn-Board Diagnostic (OBD) System Checkº
performed?
ÐGo to Step 2
Go to OBD
System
Check
21. Read the ªCautionº above.
2. Relieve the fuel system pressure and install the fuel
pump pressure gauge to the test fitting.
3. Use Tech 2 to command the fuel pump ªON.º
Is there an immediate pressure build-up which
indicates the pump is running?
ÐGo to Step 3Go to Step 4
31. Verify that the pump is not running by removing the
fuel filler cap and listening.
2. Command the pump ªONº with Tech 2.
Did the pump turn ªOFFº after 2 seconds?
Ð
Test
completed
Go to Step 12
41. Ignition ªOFF.º
2. Remove the fuel pump relay.
3. Using a test light connected to ground, probe the
battery feed to the relay.
Did the light illuminate?
ÐGo to Step 6Go to Step 5
5Repair short or open battery feed to fuel pump relay.
Is the action complete?
ÐVerify repairÐ
61. Connect a test light between the two wires that
connect to the fuel pump relay pull-in coil.
2. Ignition ªON.º
Did the test light illuminate for 2 seconds and then turn
off?
ÐGo to Step 12Go to Step 7
71. With a test light connected to battery (±), probe the
fuel pump relay connector at the wire which runs
from the relay pull-in coil to the PCM.
2. Ignition ªON.º
Did the test light illuminate for 2 seconds and then turn
off?
ÐGo to Step 8Go to Step 9
8Locate and repair open in the fuel pump relay ground
circuit.
Is the action complete?
ÐVerify repairÐ

6E±87 ENGINE DRIVEABILITY AND EMISSIONS
Fuel System Electrical Test

 
StepNo Ye s Value(s) Action
9Check for short or open between the PCM and the fuel
pump relay.
Was a problem found?
ÐVerify repairGo to Step 10
101. Check the fuel pump relay circuit for a poor terminal
connection at the PCM.
2. If a problem is found, replace terminal as necessary.
Was a problem found?
ÐVerify repairGo to Step 11
11Replace the PCM.
IMPORTANT:The replacement PCM must be
programmed. Refer to
UBS 98model year Immobilizer
Workshop Manual.
Is the action complete?ÐVerify repairÐ
121. Reconnect the fuel pump relay.
2. Disconnect the fuel pump electrical connector at the
fuel tank.
3. Using a test light connected to ground, probe the
fuel pump feed wire (harness side).
4. Command the fuel pump ªONº with Tech 2.
Did the light illuminate for 2 seconds?
ÐGo to Step 15Go to Step 13
131. Honk the horn to verify that the horn relay is
functioning.
2. Substitute the horn relay for the fuel pump relay.
3. Leave the test light connected as in step 12.
4. Command the fuel pump ªONº with Tech 2.
Did the test light illuminate for 2 seconds when the fuel
pump was commanded ªON?º
ÐGo to Step 17Go to Step 14
141. Re-connect the horn relay in its proper location.
2. Check for a short circuit, blown fuse or open circuit
between the relay and the fuel tank.
Is the action complete?
ÐVerify repairÐ
151. With the fuel pump electrical connector at the fuel
tank disconnected, connect a test light between the
feed wire and the ground wire (harness side).
2. Command the fuel pump ªONº with Tech 2.
Did the test light illuminate for 2 seconds?
ÐGo to Step 18Go to Step 16
16Repair the open circuit in the fuel pump ground wire.
Is the action complete?
ÐVerify repairÐ
171. Re-connect the horn relay in its proper location.
2. Replace the fuel pump relay.
Is the action complete?
ÐVerify repairÐ
18Replace the fuel pump.
Is the action complete?
ÐVerify repairÐ

6E±92
ENGINE DRIVEABILITY AND EMISSIONS
Fuel System Diagnosis

 
StepNo Ye s Value(s) Action
221. Command the fuel pump ªONº with Tech 2.
2. Using suitable pliers which will not damage the fuel
hose, gradually apply pressure with the pliers to
pinch the flexible fuel return hose closed.
CAUTION: Do not let the fuel pressure exceed
the second specified value.
Does the fuel pressure indicated by the fuel pressure
gauge rise above the first specified value?
376 kPa
(55 psi)
414 kPa
(60 psi)
Go to Step 11Go to Step 7
231. Command the fuel pump ªONº with Tech 2.
2. Remove the fuel filler cap and listen for the sound of
the fuel pump running.
3. Turn the pump off.
Was the fuel pump running?
ÐGo to Step 7
Go to Fuel
System
Electrical Test
Chart

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±99 ENGINE DRIVEABILITY AND EMISSIONS
Manifold Absolute Pressure (MAP) Output Check
D06RW102
Circuit Description
The manifold absolute pressure (MAP) sensor measures
the changes in the intake MAP which result from engine
load (intake manifold vacuum) and engine speed
changes; and converts these into a voltage output. The
powertrain control module (PCM) sends a 5-volt
reference voltage to the MAP sensor. As the MAP
changes, the output voltage of the sensor also changes.
By monitoring the the sensor output voltage, the PCM
knows the MAP. A lower pressure (low voltage) output
voltage will be about 1-2 volts at idle. Higher pressure
(high voltage) output voltage will be about 4-4.8 volts at
wide open throttle. The MAP sensor is also used, under
certain conditions, to measure barometric pressure,
allowing the PCM to make adjustments for different
altitudes. The PCM uses the MAP sensor to diagnose
proper operation of the EGR system, in addition to other
functions.
Test Description
IMPORTANT:Be sure to used the same diagnostic test
equipment for all measurements.
The number(s) below refer to the step number(s) on the
Diagnostic Chart.
2. Applying 34 kPa (10 Hg) vacuum to the MAP sensor
should cause the voltage to be 1.5-2.1 volts less
than the voltage at step 1. Upon applying vacuum
to the sensor, the change in voltage should be
instantaneous. A slow voltage change indicates a
faulty sensor.
3. Check the vacuum hose to the sensor for leaking or
restriction, Be sure that no other vacuum devices
are connected to the MAP hose.
IMPORTANT:Make sure the electrical connector
remains securely fastened.
4. Disconnect the sensor from the bracket. Twist the
sensor with your hand to check for an intermittent
connection. Output changes greater than 0.10 volt
indicate a bad sensor.

6E±105 ENGINE DRIVEABILITY AND EMISSIONS

The engine oil dip stick not fully seated.

The engine oil fill cap loose or missing.
Test Description
Number(s) below refer to the step number(s) on the
Diagnostic Chart.
2. The MAF system performance or ªrationalityº
diagnostic uses the MAP sensor signal along with
other input to calculate an expected airflow rate that
is then compared to the actual measured airflow
from the MAF sensor. The first few steps of this
table verify that the MAP sensor is working properly.
6. Using Freeze Frame and/or Failure Records data
may aid in locating an intermittent condition. If the
DTC cannot be duplicated, the information included
in the Freeze Frame and/or Failure Records data
can be useful in determining how many miles since
the DTC set. The Fail Counter and Pass Counter
can also be used to determine how many ignition
cycles the diagnostic reported a pass and/or a fail.
Operate the vehicle within the same Freeze Frame
conditions (RPM, load, vehicle speed , temperature,
etc.) that were noted. This will isolate when the
DTC failed.For any test that requires back probing the PCM or
component harness connectors, use the Connector
Test Adapter Kit J 35616-A. Using this kit will
prevent any damage to the harness connector
terminals.
7. Any un-metered air may cause this DTC to set.
Check the PVC system for vacuum leaks. Also
inspect the dip stick for being pulled out. Check the
oil fill cap for being loose.
8. Verifies the signal circuit from the MAF sensor
electrical connector to the PCM.
9. Verifies whether a ground and B+ circuit is available.
10. Checks a signal circuit for an open.
11. Checks for a signal circuit shorted to B+.
DTC P0101 ± MAF System Performance

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. Using a Tech 2, select ªMAPº from the Engine 1
Data List.
Is the value displayed greater than the value shown?
85 kPaGo to Step 3Go toStep 13
31. Remove the MAP sensor from the intake manifold
but leave the electrical harness connected.
2. Connect a hand operated vacuum pump to the MAP
sensor.
3. Observe the MAP display while slowly applying
vacuum up to 20º Hg as indicated on the pump
gauge.
Each 1º of vacuum applied should result in a 3 to 4 kPa
drop in the MAP sensor value on the Tech 2 and the
value should change smoothly with each increase in
vacuum.
Did the MAP value change smoothly through the entire
range of the test without any erratic readings?
ÐGo to Step 13Go to Step 4
4With 20º Hg vacuum applied to the MAP sensor, is the
MAF sensor reading the same or less than the value
shown?
34 kPaGo to Step 5Go to Step 13
5Disconnect the vacuum source from the MAP sensor.
Does the MAP sensor reading return to its original
value?
ÐGo to Step 6Go to Step 13

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