Isuzu Trooper (1998-2002 year). Service manual — part 285
6E–53
ENGINE DRIVEABILITY AND EMISSIONS
On-Board Diagnostic (OBD) System Check
Step
Action
Value(s)
Yes
No
1
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 2
Go to
No MIL
(“Check
Engine” lamp)
2
1. Ignition “OFF.”
2. Install a 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 3
Go to
Step 8
3
1. Using the Tech 2 output tests function, select MIL
(“Check Engine” lamp) dash 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 4
Go to
MIL
(“Check
Engine” lamp)
On Steady
4
Attempt to start the engine.
Did the engine start and continue to run?
—
Go to
Step 5
Go to
Cranks
But Will Not
Run
5
Select “Display DTCs” with the Tech 2.
Are any DTCs stored?
—
Go to
Step 6
Go to
Step 7
6
Are two or more of the following DTCs stored? P0107,
P0108, P0113, P0118, P0122, P0123, P0712.?
—
Go to
“Multiple
PCM
Information
Sensor DTCs
Set”
Go to
applicable
DTC table
7
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?
—
Refer
to
Typical
scan data
value
Refer to
indicated
Component
System
Checks
8
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 2
Go to
Step 9
9
Attempt to display PCM data with the Tech 2.
Does the Tech 2 display PCM engine data?
—
Go to
Step 2
Go to
Step 10
10
Replace the PCM.
IMPORTANT: The replacement PCM must be
programmed. Refer to
Powertrain Control Module
(PCM) in On-Vehicle Service.
Is the action complete?
—
Go to
Step 2
—
6E–54
ENGINE DRIVEABILITY AND EMISSIONS
A/C Clutch Control Circuit Diagnosis
D06RW085
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. The electronic thermostat may intermittently
remove the control circuit ground for the A/C thermostat
relay to prevent the evaporator from forming ice. 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:
D
The throttle is greater than 90%.
D
The ignition voltage is below 10.5 volts.
D
The engine speed is greater than 4500 RPM for 5
seconds or 5400 RPM.
D
The engine coolant temperature (ECT) is greater than
125
°
C (257
°
F).
D
The intake air temperature (IAT) is less than 5
°
C
(41
°
F).
D
The power steering pressure switch signals a cramped
position.
Diagnostic Aids
To diagnose an the intermittent fault, check for the
following conditions:
D
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.
6E–55
ENGINE DRIVEABILITY AND EMISSIONS
D
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.
A/C Clutch Diagnosis
This chart should be used for diagnosing the electrical
portion of the A/C compressor clutch circuit. A Tech 2 will
be used in diagnosing the system. The Tech 2 has the
ability to read the A/C request input to the PCM. The Tech
2 can display when the PCM has commanded the A/C
clutch “ON.” The Tech 2 should have the ability to
override the A/C request signal and energize the A/C
compressor relay.
Test Description
IMPORTANT:
Do not engage the A/C compressor
clutch with the engine running if an A/C mode is not
selected at the A/C control switch.
The numbers below refer to the step numbers on the
Diagnostic Chart:
3. This a test determine is the problem is with the
refrigerant system. If the switch is open, A/C
pressure gauges will be used to determine if the
pressure switch is faulty or if the system is partially
discharged or empty.
4. Although the normal complaint will be the A/C clutch
failing to engage, it is possible for a short circuit to
cause the clutch to run when A/C has not been
selected. This step is a test for that condition.
7. There is an extremely low probability that both relays
will fail at the same time, so the substitution process
is one way to check the A/C Thermostat relay. Use
a known good relay to do a substitution check.
9. The blower system furnishes a ground for the A/C
control circuit, and it also shares a power source
through the Heater and A/C Relay. The blower
must be “ON” in order to test the A/C system.
A/C Clutch Control Circuit Diagnosis
Step
Action
Value(s)
Yes
No
1
Was the “On-Board Diagnostic (OBD) System Check”
performed?
—
Go to
Step 2
Go to
OBD
System
Check
2
Are any other DTCs stored?
—
Go to the
other DTC
chart(s) first
Go to
Step 3
3
1. Disconnect the electrical connector at the pressure
switch located on the receiver/drier.
2. Use an ohmmeter to check continuity across the
pressure switch.
Is the pressure switch open?
—
Go to Air
Conditioning
to diagnose
the cause of
the open
pressure
switch
Go to
Step 4
4
IMPORTANT: Before continuing with the diagnosis, the
following conditions must be met:
D
The intake air temperature must be greater than
15
°
C. (60
°
F).
D
The engine coolant temperature must be less
than 119
°
C (246
°
F).
1. A/C “OFF.”
2. Start the engine and idle for 1 minute.
3. Observe the A/C compressor.
Is the A/C compressor clutch engaged even though
A/C has not been requested?
—
Go to
Step 45
Go to
Step 5
5
1. Idle the engine.
2. A/C “ON”.
3. Blower “ON”.
4. Observe the A/C compressor.
Is the A/C compressor magnetic clutch engaged?
—
Refer to
Diagnostic
Aids
Go to
Step 6
6E–56
ENGINE DRIVEABILITY AND EMISSIONS
A/C Clutch Control Circuit Diagnosis
(Cont'd)
Step
No
Yes
Value(s)
Action
6
1. Engine idling.
2. A/C “ON”.
3. Blower “ON”.
4. Observe the “A/C Request” display on the Tech 2.
Does the tool “A/C Request” display indicate “Yes?”
—
Go to
Step 34
Go to
Step 7
7
Temporarily substitute the A/C compressor relay in
place of the A/C thermostat relay, then repeat Step 5.
Did the “A/C Request” display indicate “Yes?”
—
Go to
Step 8
Go to
Step 9
8
Replace the original A/C thermostat relay.
Is the action complete?
—
Verify repair
—
9
Dose the blower operate?
—
Go to
Step 10
Go to
Step 11
10
Repair the blower.
Is the action complete?
—
Verify repair
—
11
Check for a faulty 10a A/C fuse in the underdash fuse
panel.
Was the 10A fuse OK?
—
Go to
Step 13
Go to
Step 12
12
Check for short circuit and make repairs if necessary.
Replace the 10A A/C fuse.
Is the action complete?
—
Verify repair
—
13
1. Ignition “ON.”
2. Use a DVM to check voltage at the positive A/C
switch wire (BRN).
Was voltage equal to the specified value?
+B
Go to
Step 15
Go to
Step 14
14
Repair the open wire (BRN) between the A/C switch
and the A/C fuse.
Is the action complete?
—
Verify repair
—
15
1. Remove the glove box to gain access to the A/C
thermostat.
2. Disconnect the thermostat connector.
3. Attach a fused jumper between ground and the
PNK/GRN wire at the thermostat.
4. A/C “ON.”
5. Blower “ON.”
Dose A/C request indicate “YES” on the Tech 2?
—
Go to
Step 16
Go to
Step 23
16
1. Ignition “ON.”
2. Use a DVM to check voltage at the electronic A/C
thermostat.
Was voltage equal to the specified value?
+B
Go to
Step 20
Go to
Step 17
17
Check for an open (LT GRN) between the thermostat
and the A/C switch.
Was the wire open?
—
Go to
Step 18
Go to
Step 19
18
Repair the open wire (LT GRN) between the thermostat
and the A/C switch.
Is the action complete?
—
Verify repair
—
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