Isuzu 2008MY N Series Workshop Manual page 206

Step
1. Test the vehicle speed signal circuit between
the ECM (pin 19 of J-14) and the EHCU (pin
14 of J-22) for an open circuit or high
resistance.
7
2. Repair the circuit(s) as necessary.
Did you find and correct the condition?
1. Inspect for an intermittent and for poor
connections at the harness connector of the
EHCU (pins 14 of J-22).
8
2. Repair the connection(s) as necessary.
Did you find and correct the condition?
1. Turn OFF the ignition.
2. Disconnect the ECM harness connector.
3. Inspect for an intermittent and for a poor
connection at the harness connector of the
9
ECM (pin 19 of J-14).
4. Repair the connection(s) as necessary.
Did you find and correct the condition?
Important:
programmed.
Replace the EHCU. Refer to EHCU in Section 4C1
10
ABS/ASR.
Did you complete the replacement?
Important:
programmed and learned.
11
Replace the ECM. Refer to ECM Replacement.
Did you complete the replacement?
1. Reconnect all previously disconnected fuse or
harness connector(s).
2. Clear the DTCs with a scan tool.
3. Turn OFF the ignition for 30 seconds.
4. Start the engine.
12
5. Operate the vehicle within the Conditions for
Running the DTC. You may also operate the
vehicle
observed from the Freeze Frame/ Failure
Records.
Did the DTC fail this ignition?
Observe the DTC Information with a scan tool.
13
Are there any DTCs that you have not
diagnosed?
Circuit/ System Testing DTC P0503 (Model without ABS)
Step
Did you perform the Diagnostic System Check
1
- Engine Controls?
Action
Replacement EHCU
Replacement ECM
within the conditions
Action
Engine Control System (4HK1)
Value(s)
—
—
—
must be
—
must be
—
—
that you
—
Value(s)
—
Yes
Go to Step 12 Go to Step 9
Go to Step 12 Go to Step 10
Go to Step 12 Go to Step 11
Go to Step 12
Go to Step 12
Go to Step 3 Go to Step 13
Go to DTC List
Yes
Go to Diagnostic
System Check -
Go to Step 2 Engine Controls
1A-203
No
—
—
System OK
No