Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Check Power Supply And Ground Line Of Engine Control Module (ECM)
- After servicing or replacing faulty parts, perform Clear Memory Mode. Ref. to ENGINE (DIAGNOSTICS) (H4DO)>CLEAR MEMORY MODE>OPERATION ., and inspection mode. Ref. to ENGINE (DIAGNOSTICS) (H4DO)>INSPECTION MODE>PROCEDURE .
- Use the check board when measuring the ECM terminal voltage and resistance.
Wiring diagram:
Engine Electrical System. Ref. to WIRING SYSTEM>ENGINE ELECTRICAL SYSTEM>WIRING DIAGRAM .
- CHECK MAIN RELAY
.
- Turn the ignition switch to OFF.
- Remove the main relay.
- Check the main relay. Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DO)>MAIN RELAY>INSPECTION
.
Is the check result OK?
Yes
Go to 2 .
No
Replace the main relay. Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DO)>MAIN RELAY .
- CHECK GROUND CIRCUIT FOR ECM
.
- Disconnect the connector from ECM.
- Measure the resistance of harness between ECM connector and chassis ground.
Connector & terminal
(E158) No. 61 - Chassis ground:
(E158) No. 62 - Chassis ground:
(E158) No. 63 - Chassis ground:
(E158) No. 64 - Chassis ground:
(E158) No. 65 - Chassis ground:
Is the resistance less than 5 Ω?
Yes
Go to 3 .
No
Open circuit of harness between ECM connector and engine ground terminal
- CHECK INPUT VOLTAGE OF ECM
.
- Turn the ignition switch to ON.
- Measure the voltage between ECM connector and chassis ground.
Connector & terminal
(B134) No. 2 (+) - Chassis ground (-):
(B134) No. 27 (+) - Chassis ground (-):
Is the voltage 10 V or more?
Yes
Go to 4 .
No
Repair the open or ground short in the harness of power supply circuit.
- CHECK INPUT VOLTAGE OF MAIN RELAY
.
Measure the voltage between M/B (main relay) terminal and chassis ground. Terminals
No. 1 (+) - Chassis ground (-):
No. 2 (+) - Chassis ground (-):
Is the voltage 10 V or more?
Yes
Go to 5 .
No
Repair the open or ground short in the harness of power supply circuit.
- CHECK INPUT VOLTAGE OF ECM
.
- Turn the ignition switch to OFF.
- Install the main relay.
- Measure the voltage between ECM connector and chassis ground.
Connector & terminal
(B134) No. 60 (+) - Chassis ground (-):
Is the voltage 10 V or more?
Yes
Go to 6 .
No
Repair the open circuit of harness between ECM connector and M/B (main relay) terminal.
- CHECK INPUT VOLTAGE OF ECM
.
- Connect the connector to ECM.
- Turn the ignition switch to ON.
- Measure the voltage between ECM connector and chassis ground.
Connector & terminal
(B134) No. 1 (+) - Chassis ground (-):
(B134) No. 14 (+) - Chassis ground (-):
Is the voltage 10 V or more?
Yes
Check ignition control system. Ref. to ENGINE (DIAGNOSTICS) (H4DO)>DIAGNOSTICS FOR ENGINE STARTING FAILURE>IGNITION CONTROL SYSTEM .
No
Repair the harness and connector.
NOTE: In this case, repair the following item:- Open circuit of harness between ECM connector and M/B (main relay) connector
- Poor contact of M/B (main relay) connector
- Poor contact of ECM connector
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.
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