Isuzu Trooper (1998-2002 year). Manual - part 423

6E–62

6VE1 3.5 ENGINE DRIVEABILITY AND EMISSIONS

On-Board Diagnostic (OBD) System Check

D06RY00053

Circuit Description

The on-board diagnostic system check is the starting
point for any driveability complaint diagnosis. Before
using this procedure, perform a careful visual/physical
check of the PCM and engine grounds for cleanliness and
tightness.
The on-board diagnostic system check is an organized
approach to identifying a problem created by an
electronic engine control system malfunction.

Diagnostic Aids

An intermittent may be caused by a poor connection,
rubbed–through wire insulation or a wire broken inside the
insulation. Check for poor connections or a damaged
harness. Inspect the PCM harness and connector 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. The MIL (“Check Engine lamp”) should be “ON”

steady with the ignition “ON ” and the engine “OFF”.
If not, the “No MIL” chart should be used to isolate
the malfunction.

3. The SVS (“Service Vehicle Soon”) lamp should be

“ON” steady with the ignition “ON ”and the engine
“OFF”. If not, the “No SVS lamp”chart should be
used to isolate the malfunction.

4. Checks the Class 2 data circuit and ensures that the

PCM is able to transmit serial data.

5. This test ensures that the PCM is capable of

controlling the MIL (“Check Engine lamp”) and the
MIL (“Check Engine lamp”) driver circuit is not
shorted to ground.

6. This test ensures that the PCM is capable of

controlling the SVS (“Service Vehicle Soon”) lamp
and the SVS (“Service Vehicle Soon”) lamp driver
circuit is not shorted to ground.

8. Check the DTCs (System ,Volts Supply circuit).

9. Check the DTCs (PCM{Software} detect Errors).

12.If the engine will not start, the Cranks But Will Not

Run chart should be used to diagnose the condition.

15.A Tech 2 parameter which is not within the typical

range may help to isolate the area which is causing
the problem.

16.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

PCM

Replacement and Programming Procedures in
Powertrain Control Module (PCM) and Sensors of
this section.

11.If the starter motor will not start, the starter control

system chart should be used to diagnose the
condition.

6E–63

6VE1 3.5L ENGINE DRIVEABILITY AND EMISSIONS

On-Board Diagnostic (OBD) System Check

Step

Action

Value(s)

Yes

1. Ignition “ON”, engine “OFF”.
2. Observe the Service Vehicle Soon (SVS) lamp.

Is the SVS lamp flashing?

—

Refer to

Immobilizer

System

Workshop

Manual

Go to

Step 2

1. Ignition “ON”, engine “OFF”.
2. Observe the malfunction indicator lamp (MIL or

“Check Engine lamp”).

Is the MIL (“Check Engine lamp”)“ON”?

—

Go to

Step 3

Go to

MIL(“Check

Engine lamp”)

1. Ignition “ON”, engine “OFF”.
2. Observe the SVS (“Service Vehicle Soon”) lamp.

Is the SVS (“Service Vehicle Soon”) lamp “ON”?

—

Go to

Step 4

Go to

SVS

(“Service

Vehicle

Soon”) lamp

1. Ignition “OFF”.
2. Install Tech 2.
3. Ignition “ON”.
4. Attempt to display PCM engine data with the

Tech 2.

Does the Tech 2 display PCM data?

—

Go to

Step 5

Go to

Step 13

1. Using the Tech 2 output tests function, select MIL

(“Check Engine lamp”) control and command the
MIL (“Check Engine Lamp”) “OFF”.

2. Observe the MIL (“Check Engine lamp”).

Did the MIL (“Check Engine lamp”) turn “OFF”?

—

Go to

Step 6

Go to

MIL(“Check

Engine lamp”)

On Steady

1. Using the Tech 2 output tests function, select RPL

(“Reduced Power lamp”) control and command the
RPL (“Reduced Power lamp”) “OFF”.

2. Observe the SVS (“Service Vehicle Soon”) lamp.

Did the SVS (“Service Vehicle Soon”) lamp turn “OFF”?

—

Go to

Step 7

Go to

SVS

(“Service

Vehicle

Soon”) lamp

On Steady

Select “Display DTCs” with the Tech 2.

Are any DTCs stored?

—

Go to

Step 8

Go to

Step 12

Stored DTCs.
P0562, P0563, P0601, P0602, P0604, P0606, P1625,
P1635, P1639, P1640, P1650

Are the applicable DTCs stored?

—

Go to

applicable
DTC table

Go to

Step 9

Stored DTCs.
P1514, P1515, P1516, P1523, P1125, P1290, P1295,
P1299

Are the applicable DTCs stored?

—

Go to

applicable
DTC table

Go to

Step 10

Stored DTCs.

1. P0425, P0106, P0107, P1107, P0401, P1404,

P0405, P1120, P1221, P1515, P1516, P1275,
P1635, P1271, P1273, P1285, P1272

2. P0336, P0337, P1220, P1515, P1221, P1516,

P1280, P1639, P1271, P1272

Are the applicable DTCs stored?

—

Go to

“Multiple

PCM

Information

sensor DTCs

Set”

Go to

Step 11

6E–64

6VE1 3.5 ENGINE DRIVEABILITY AND EMISSIONS

On-Board Diagnostic (OBD) System Check

(Cont'd)

Step

Yes

Value(s)

Action

Attempt to crank the starter motor

Did the starter motor crank?

—

Go to

Step 11

Go to

Starter

control

system

Attempt to start the engine.

Did the engine start and continue to run?

—

Go to

Step 7

Go to

Cranks

But Will Not

Run

Compare PCM data values displayed on the Tech 2 to
the typical engine scan data values.

Are the displayed values normal or close to the typical
values?

—

Go to

Symptom

Refer to

indicated

Component

System
Checks

1.  Ignition “OFF”, disconnect the PCM.
2.  Ignition “ON”, engine “OFF”.
3.  Check the Class 2 data circuit for an open, short to

ground, or short to voltage. Also, check the DLC
ignition feed circuit for an open or short to ground
and the DLC ground circuit for an open.

4. If a problem is found, repair as necessary.

Was a problem found?

—

Go to

Step 3

Go to

Step 15

1. Attempt to reprogram the PCM. Refer to

Powertrain

Control Module (PCM) in On-Vehicle Service.

2. Attempt to display PCM data with the Tech 2.

Does the Tech 2 display PCM engine data?

—

Go to

Step 3

Go to

Step 16

Replace the PCM.

IMPORTANT: The replacement PCM must be
programmed. Refer to

ON-Vehicle Service in Power

Control Module and Sensors for procedures.

And also refer to latest Service Bulletin. Check to see
if the latest software is released or not. And then Down
Load the LATEST PROGRAMMED SOFTWARE to the
replacement PCM.

Is the action complete?

—

Go to

Step 3

—

6E–65

6VE1 3.5L ENGINE DRIVEABILITY AND EMISSIONS

A/C Clutch Control Circuit Diagnosis

D06RY00159

Circuit Description

When air conditioning and blower fan are selected, and if
the system has a sufficient refrigerant charge, a 12-volt
signal is supplied to the A/C request input of the
powertrain control module (PCM). The A/C request
signal may be temporarily canceled during system
operation by the electronic thermostat in the evaporator
case. When the A/C request signal is received by the
PCM, the PCM supplies a ground from the compressor
clutch relay if the engine operating conditions are within
acceptable ranges. With the A/C compressor relay
energized, voltage is supplied to the compressor clutch
coil.
The PCM will enable the compressor clutch to engage
whenever A/C has been selected with the engine running,
unless any of the following conditions are present:

The throttle is greater than 90%.

The ignition voltage is below 10.5 volts.

The engine speed is greater than 4500 RPM for 5
seconds or 5400 RPM.

The engine coolant temperature (ECT) is greater
than 125

C (257

F).

The intake air temperature (IAT) is less than 5

(41

F).

The power steering pressure switch signals a high
pressure condition.

Diagnostic Aids

To diagnose an the intermittent fault, check for following
conditions:

Poor connection at the PCM–Inspect connections for
backed-out terminals, improper mating, broken locks,
improperly formed or damaged terminals, and poor
terminal-to-wire connection.

Damaged harness–Inspect the wiring harness for
damage. If the harness appears to OK, observe the
A/C clutch while moving connectors and wiring
harnesses related to the A/C. A sudden clutch
malfunction will indicate the source of the intermittent
fault.

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