Engine Hot Lamp Output Control Circuit Malfunction
P0655 indicates a malfunction in the engine hot lamp output control circuit, typically between the PCM and the instrument cluster. This code prevents the engine temperature warning lamp from functioning properly, which can fail to alert the driver of engine overheating conditions.
What You Might Notice
- Engine hot lamp inoperative or not illuminating when it should
- Engine hot lamp illuminated constantly regardless of engine temperature
- Engine drivability issues
- Warning lamp flickering intermittently
- No warning indicator during actual engine overheating
Most Common Causes
- 1
Open or shorted wiring harness
Damaged, corroded, or disconnected wiring between the PCM and instrument cluster causes signal loss or short circuits in the lamp control circuit.
- 2
Faulty PCM output driver
The power control module's lamp driver circuit has failed internally, preventing proper signal transmission to the warning lamp.
- 3
Defective instrument cluster
The instrument panel module or lamp circuit within the cluster is malfunctioning and cannot receive or process the lamp control signal from the PCM.
- 4
Engine coolant temperature sensor malfunction
A failing coolant temp sensor provides incorrect readings to the PCM, disrupting proper lamp control circuit operation and temperature warning logic.
How to Diagnose It
- 1
Check Open or shorted wiring harness — Damaged, corroded, or disconnected wiring between the PCM and instrument cluster causes signal loss or short circuits in the lamp control circuit.
- 2
Check Faulty PCM output driver — The power control module's lamp driver circuit has failed internally, preventing proper signal transmission to the warning lamp.
- 3
Check Defective instrument cluster — The instrument panel module or lamp circuit within the cluster is malfunctioning and cannot receive or process the lamp control signal from the PCM.
- 4
Check Engine coolant temperature sensor malfunction — A failing coolant temp sensor provides incorrect readings to the PCM, disrupting proper lamp control circuit operation and temperature warning logic.
How to Fix It
- 1
Inspect and repair wiring harness
Visually inspect the wiring between the PCM and instrument cluster for breaks, corrosion, or loose connectors. Repair or replace damaged sections and ensure all connections are clean and tight.
- 2
Test PCM lamp driver output
Use a diagnostic scanner to command the lamp on and off while monitoring voltage at the lamp control connector. If no signal is present, the PCM driver circuit has failed and requires PCM replacement or reprogramming.
- 3
Test and replace instrument cluster if needed
Connect a test light to the lamp control circuit at the instrument cluster. If the test light does not illuminate when the PCM sends the signal, the cluster lamp circuit is faulty and the cluster must be replaced or repaired.
- 4
Check coolant temperature sensor
Test the engine coolant temperature sensor resistance values against manufacturer specs. If readings are out of range or the sensor is unresponsive, replace it with an OEM or quality equivalent part.
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