Engine Hot Lamp Output Control Circuit
Diagnostic trouble code P0655 indicates that the powertrain control module (PCM) has detected an electrical fault in the control circuit for the engine hot warning lamp. The PCM sets this code when the voltage signal from the warning lamp circuit does not match the expected parameters, meaning the light may fail to illuminate during an actual overheating event.
While this code does not affect engine performance directly, it is important to fix it soon. If the engine overheats, the driver will not receive a warning light, which could lead to catastrophic engine damage.
Common symptoms
- Illumination of the Check Engine Light (MIL)
- The engine hot warning lamp fails to illuminate during the initial key-on bulb check
- The engine hot warning lamp remains illuminated continuously while driving
- Inoperative temperature gauge (on some shared-circuit vehicles)
- Lack of visual warning if the engine actually overheats
Likely causes
- Burned out engine hot warning lamp bulb or failed LED in the instrument cluster
- Corroded, damaged, or loose wiring in the warning lamp control circuit
- Faulty instrument cluster or printed circuit board
- Poor electrical connection at the PCM or instrument cluster connectors
- Faulty Powertrain Control Module (PCM) or PCM programming error
What to check before replacing parts
Perform a key-on, engine-off (KOEO) bulb check.
Look for: Observe the instrument cluster to see if the engine hot lamp illuminates briefly; if it does not, the bulb or LED may be burned out.
Use a bi-directional scan tool to command the engine hot lamp on and off.
Look for: If the scan tool can turn the light on, the wiring to the cluster is likely intact and the issue may be intermittent or PCM-related. If it cannot, the fault is in the cluster, bulb, or wiring.
Visually inspect the wiring harness and connectors between the PCM and the instrument cluster.
Look for: Look for chafed wires, broken pins, or corrosion that could cause an open or short circuit in the lamp control line.
Test the lamp control circuit for continuity and resistance using a digital multimeter.
Look for: Disconnect the PCM and cluster connectors and measure the wire; resistance should be less than 1 ohm, and there should be no continuity to ground or power.
Test the PCM output signal for the warning lamp.
Look for: Back-probe the PCM connector and verify if the PCM is providing the correct ground or voltage signal to activate the lamp when commanded; a missing signal indicates a faulty PCM.
This page explains the generic P0655 definition and is general reference information, not a diagnosis for your specific vehicle. Actual causes, severity, and repairs vary by make, model, engine, and mileage — always confirm with a scan tool and a qualified technician before replacing parts.
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