Isuzu 4HL1, Workshop Manual

Page: 132 / 267

1A-130 Engine Control System
Diagnostic Aids
Poor connection or damaged harness may cause
intermittents. Check for the following conditions and, if
the fault is detected, repair or replace the faulty portion.
• Poor connection at ECM: Inspect harness
connectors for backed-out pins, improper mating,
broken locks, improperly formed or damaged pins,
and poor pin-to-wire connection.
• Damaged harness: Inspect the wiring harness for
rubbed-through wire insulation or wire broken
inside the insulator. If the harness appears to be
OK, observe the display on Tech 2 while moving
connectors and wiring harnesses related to the
sensor. A change in the display will indicate the
location of the fault.
Test Description
Number(s) below refer to the step number(s) on the
Diagnostic Chart.
3. If the DTC is not detected, the possible cause is
intermittent (intermittent fault).
Step Action Value(s) Yes No
1
Perform the "On-Board Diagnostic (OBD)
System Check".
Was the OBD System Check performed?
—
Go to Step 2
Refer to OBD
System Check
and go to Step 2
2
Check the ECM connector for installation and,
if mounted improperly, connect it certainly.
Is the action complete?
—
Go to Step 3 —
3
Review the DTC.
1. Using Tech 2, check and store the DTC.
2. Clear the DTC.
3. Perform test run and review the DTC.
Is DTC34 detected?
—
Go to Step 4
Refer to
Diagnostic Aids
4
Check the injector drive circuit for +B short.
1. Starter switch "OFF".
2. Disconnect the ECM.
3. At the ECM connector pins, measure the
resistance.
Was the resistance within range?
Pins 1/2/4/5-
109/114/115/
116:
∞ Ω
Go to Step 5 Go to Step 6
5
Check the ECM ground circuit for open wiring.
1. Starter switch "OFF".
2. Disconnect the ECM.
3. Measure the resistance between ECM
connector pin and ground (e.g., frame or
body)
Was the resistance within range?
Pins 87/95/
119/120/121-
ground: 0
Ω
Go to Step 7 Go to Step 6
6
Repair or replace the faulty harness.
Is the action complete?
—
Verify repair and
go to Step 7 —
7
1. 1. Replace the ECM.
IMPORTANT:
If necessary (for the vehicle equipped with
idle stop function), input the number of
startups to the replacing ECM.
Is the action complete?
—
Verify repair and
go to Step 8 —