Isuzu 4HL1 Workshop Manual page 57

Step
Perform the "On-Board Diagnostic (OBD)
System Check".
1
Was the OBD System Check performed?
Check the circuit between ECM and CHECK
ENGINE lamp for short to ground.
1. Starter switch "OFF".
2. Disconnect the ECM.
2
3. Starter switch "ON", and observe the
CHECK ENGINE lamp.
Is the CHECK ENGINE lamp "OFF"?
Repair or replace the harness between ECM
and CHECK ENGINE lamp.
3
Is the action complete?
Check the diagnostic switch circuit for open
wiring.
1. Disconnect the ECM.
2. Short DLC pins 4 and 6.
4
3. Check the continuity between ECM
connector pin and ground (e.g., frame or
body).
Is the circuit in normal condition?
Check the DLC ground circuit for open wiring.
1. Check the continuity between DLC pin
5
and ground (e.g., frame or body).
Is the circuit in normal condition?
Repair or replace the DLC ground circuit
harness.
6
Is the action complete?
Repair or replace the harness between ECM
and DLC pin 6.
7
Is the action complete?
Re-observe the CHECK ENGINE lamp for
operation.
1. Certainly connect connectors.
2. Short DLC pins 4 and 6.
8
3. Starter switch "ON", and observe the
CHECK ENGINE lamp.
Does the CHECK ENGINE lamp blink?
1. Replace the ECM.
Important:
If necessary (for the vehicle equipped with
9
idle stop function), input the number of
startups to the replacing ECM.
Is the action complete?
Action
Engine Control System 1A-55
Value(s)
—
Go to Step 2
—
Go to Step 4
—
Verify repair and
go to Step 10
ECM pin 112-
ground:
Continued
Go to Step 8
DLC 4/5 pin-
ground:
Continued
Go to Step 7
—
Verify repair and
go to Step 10
—
Verify repair and
go to Step 10
—
Refer to
"Diagnostic Aids"
—
Verify repair and
go to Step 10
Yes No
Refer to OBD
System Check
and go to Step 2
Go to Step 3
Go to Step 5
Go to Step 6
Go to Step 9
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