Isuzu 2008MY N Series Workshop Manual page 234

Circuit/ System Testing DTC P0687
Step
Did you perform the Diagnostic System Check
1
- Engine Controls?
1. Install a scan tool.
2. Turn OFF the ignition for 30 seconds.
3. Turn ON the ignition, with the engine OFF.
2
4. Monitor the DTC Information with a scan tool.
Does the DTC fail this ignition?
1. Turn OFF the ignition for 30 seconds.
2. Remove the ECM main relay.
3
3. Turn ON the ignition, with the engine OFF.
Is DTC P0685 set?
1. Turn OFF the ignition for 30 seconds.
2. Replace the ECM main relay with the glow
relay or replace with a known good relay.
4
3. Turn ON the ignition, with the engine OFF.
Does the DTC fail?
Repair the short to battery on the battery voltage
feed circuits between the ECM (pins 2 and 5 of J-
5
14) and the ECM main relay (pin 2 of X-18)
Did you complete the repair?
Repair the short to battery on the battery voltage
supply circuits between the ECM (pins 21 and 40 of
6
J-14) and the ECM main relay (pin 3 of X-18)
Did you complete the repair?
Replace the ECM main relay.
7
Did you complete the replacement?
1. Reconnect all previously disconnected relay
or harness connector(s).
2. Clear the DTCs with a scan tool.
8
3. Turn OFF the ignition for 30 seconds.
4. Turn ON the ignition.
Did the DTC fail this ignition?
Observe the DTC Information with a scan tool.
9
Are there any DTCs that you have not
diagnosed?
Action
Engine Control System (4HK1)
Value(s) Yes
—
Go to Step 2
—
Go to Step 3
—
Go to Step 4
—
Go to Step 6
—
Go to Step 8
—
Go to Step 8
—
Go to Step 8
—
Go to Step 3
—
Go to DTC List
1A-231
No
Go to Diagnostic
System Check -
Engine Controls
Go to Diagnostic
Aids
Go to Step 5
Go to Step 7
—
—
—
Go to Step 9
System OK