Isuzu 4JA1 Workshop Manual page 299

Step
8 Important: An open in a ground circuit at the ECM
will not cause a loss of communication.
1. Check ECM ground for corrosion and tightness.
2. Clean or tighten grounds as necessary.
Did you find and correct the condition?
9 1. Turn OFF the ignition.
2. Reconnect the ECM harness connector if
previously disconnected.
3. Turn ON the ignition, with the engine OFF.
4. Replace the ECM main relay with the tail relay or
replace with a known good relay.
5. Attempt to establish scan tool communications
with the ECM.
Does the ECM communicate with the scan tool?
10 1. Turn OFF the ignition.
2. Remove the ECM main relay.
3. Turn ON the ignition, with the engine OFF.
4. Using a test lamp, check for battery voltage at
both of the battery voltage supply circuits to the
ECM main relay (pins 2 and 5 of X-12
connector).
5. Repair the open in the circuit(s) as necessary.
Did you find and correct the condition?
11 1. Reinstall the ECM main relay.
2. Turn the ignition ON and OFF while listening or
feeling for the ECM main relay click. Wait 2
seconds between transitions.
Does the ECM main relay click when the ignition is
turned ON or OFF?
12 Repair the ECM main relay control circuit between
the ECM main relay (pin 4 of X-12 connector) and
the ECM (pin 56 of C-56 connector) for the following
conditions:
•
An open circuit
•
A short to battery or ignition voltage
•
High resistance or a poor connection at
both the ECM and ECM main relay
Did you find and correct the condition?
13 1. Check ECM main relay voltage supply circuit to
the ECM between the ECM main relay (pin 1 of
X-12 connector) and the ECM (pin 41 of C-56
connector) for the following conditions:
•
An open circuit
•
High resistance or a poor connection at the
ECM and ECM main relay
2. Repair the circuit(s) as necessary.
Did you find and correct the condition?
14 Repair the open in the ignition voltage circuit to the
ECM.
Did you complete the repair?
15 Replace the ECM main relay.
Did you complete the replacement?
16 Important: Replacement
programmed.
Replace the ECM. Refer to Engine Control Module
(ECM) Replacement in this section.
Did you complete the replacement?
Action
ECM must
Engine Control System (4JH1) 6E-45
Value(s)
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be
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Yes
Go to Step 17 Go to Step 9
Go to Step 15 Go to Step 10
Go to Step 17 Go to Step 11
Go to Step 13 Go to Step 12
Go to Step 17 Go to Step 16
Go to Step 17 Go to Step 16
Go to Step 17
Go to Step 17
Go to Step 17
No
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