Staff Answer
Sep 17, 2026 - 01:30 PM
1. Primary Causes of Code P0655
| Category | Cause | Description |
| Circuit Fault | Shorted or Open Wiring | Chafed signal wire shorted to ground or broken wire between PCM and instrument cluster. |
| Cluster Assembly | Failed Hot Warning Lamp | Blown incandescent bulb or damaged LED/printed circuit board in the instrument panel. |
| Sensor Failure | Out-of-Spec ECT Sensor | Faulty coolant temperature sensor providing erratic resistance values to the PCM. |
| Connector Issue | Corroded Pin Connections | Loose, rusted, or bent pins at the PCM harness or instrument cluster bulkhead plug. |
| Control Module | Internal PCM Driver Error | Internal output transistor failure inside the PCM responsible for lamp illumination. |
2. Common Symptoms
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Check Engine Light (CEL) illuminated.
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Engine Hot / Temperature warning light stays on constantly even with a cold engine.
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Temperature warning light fails to turn on during the initial key-on bulb check routine.
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Inaccurate or erratic gauge readings on the instrument cluster.
3. Common Vehicle Applications
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Applies to OBD2-compliant vehicles with dedicated output circuits for engine over-temperature lights, including models from General Motors (Chevrolet, GMC, Pontiac, Buick), Ford, Chrysler, and European imports.
4. Step-by-Step Diagnostic & Troubleshooting Procedure
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Connect an OBD2 scanner, read code P0655, and monitor live ECT sensor data. Verify if the coolant temperature matches actual engine status (use an infrared thermometer at the thermostat housing).
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Perform a bulb check by cycling the ignition key to RUN without starting. Check if the high-temperature warning light illuminates briefly.
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Access bi-directional scanner controls (if supported) to command the Engine Hot Lamp ON and OFF. Check if the dashboard light responds to the PCM signal.
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Inspect the wiring harness connecting the PCM to the instrument cluster. Test for continuity, short to ground, and short to voltage using a Digital Multimeter (DMM).
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Disconnect the instrument cluster plug and inspect connector pins for corrosion, water intrusion, or backed-out terminals.
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Verify bulb or LED circuit integrity on the instrument cluster circuit board. Replace faulty wiring, bulb/cluster components, or the ECT sensor as needed before clearing codes.
For detailed diagnostic schematics, OBD2 error code databases, and repair guides, visit our complete video:
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