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.
ECM Power Supply & Ground Tests
- Check Main Relay - Turn ignition off and remove main relay. Connect battery voltage to main relay terminals No. 1 and 2. Check resistance between main relay terminals No. 3 and 5, and terminals No. 4 and 6. See appropriate wiring diagram in WIRING DIAGRAMS article. Resistance should be less than 10 ohms in both tests. If resistance is as specified, go to next step. If resistance is not as specified, replace main relay.
- Check ECM Power Supply Circuit
- Reconnect main relay and disconnect ECM harness connector. Turn ignition on. Using DVOM, check voltage between the following ECM harness connector terminals:
- Terminals No. 1 and 19
- Terminals No. 2 and 19
- Terminals No. 39 and 19
Voltage reading on each listed terminal should be greater than 10 volts. If voltage reading is as specified, go to next step. If voltage reading is not as specified, check and repair circuit between main relay and ECM harness connector. See appropriate wiring diagram in WIRING DIAGRAMS article.
- Check ECM Ground Circuit
- Turn ignition off. Disconnect ECM harness connector. Using DVOM, check resistance between chassis ground and the following ECM harness connector terminals:
- Terminal No. 17
- Terminal No. 18
- Terminal No. 19
- Terminal No. 20
- Terminal No. 42
- Terminal No. 46
- Terminal No. 69
- Terminal No. 94
- Terminal No. 95
Resistance on each listed terminal should be less than 5 ohms. If resistance is as specified, see IGNITION CONTROL SYSTEM TESTS . If resistance is not as specified, check affected ground circuit between ECM harness connector or check for poor terminal contact in harness connector. See appropriate wiring diagram in WIRING DIAGRAMS article.
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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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