Isuzu 4HL1 Workshop Manual page 59

Diagnostic Aids
An intermittent may be caused by a poor connection, a
rubbed-through wire insulation, or a wire broken inside
the insulator. Check for the following conditions and, if
a fault is found, perform repair or replacement.
• Poor connection
connectors for backed-out pins, improper mating,
broken locks, improperly formed or damaged pins,
and poor pin-to-wire connection.
Step
Perform the "On-Board Diagnostic (OBD)
System Check".
1
Was the OBD System Check performed?
Check the SBF (ECU: 50 A, engine controller:
50 A) and fuse (engine controller: 10 A).
2
Are the SBF and fuse in normal condition?
Replace the SBF or fuse.
3
Is the action complete?
Check the ON signal is input to the ECM from
the starter switch.
1. Disconnect the ECM.
2. Starter switch "ON".
4
3. Measure the voltage between ECM
connector pin and ground (e.g., frame or
body)
Was the voltage within range?
Repair or replace the harness between starter
switch and ECM pin 109.
5
Is the action complete?
Check the power supply voltage is applied to
the main relay.
1. Remove the main relay.
2. Starter switch "ON".
6
3. Measure the voltage between main relay
connector (pin 1) and ground (e.g., frame
or body).
Was the voltage within range?
Check the power supply voltage is applied to
the SBF (engine controller: 30 A).
1. Remove the SBF.
2. Starter switch "ON".
7
3. Measure
connector.
Was the voltage within range?
Repair or replace the harness between SBF
(engine controller: 30 A) and main relay.
8
Is the action complete?
at ECM: Inspect
Action
the voltage at the
• Damaged harness: Inspect the wiring harness for
rubbed-through wire insulation or wire broken
inside the insulator.
harness
Value(s)
—
—
—
Pin 109-
ground:
16 ~ 24V
—
16 ~ 32 V
16 ~ 32 V
SBF
—
Engine Control System 1A-57
Yes
Go to Step 2 and go to Step 2
Go to Step 4
Verify repair and
go to Step 4
Go to Step 6
Verify repair and
go to Step 6
Go to Step 10
Verify repair and
go to Step 9
Verify repair and
go to Step 10
No
Refer to OBD
System Check
Go to Step 3
—
Go to Step 5
—
Go to Step 7
Go to Step 8
—