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P0655Engine Hot Lamp Output Control Circuit

The circuit that drives the engine hot (overheat) warning lamp has an electrical fault detected by the PCM.

Definition

The PCM controls the engine hot warning lamp output and monitors the driver circuit for opens and shorts; P0655 sets when the circuit state does not match the commanded state. The engine will run normally, but the overheat warning lamp may be inoperative or stuck on, which matters because the driver could miss a genuine overheating event. This code concerns the lamp circuit only — it does not indicate the engine actually overheated, and coolant temperature sensor readings are usually normal.

Common causes

  • Open or shorted wiring in the hot lamp circuit between the PCM and instrument cluster
  • Burned-out warning lamp bulb or failed cluster LED drive
  • Corroded or loose terminals at the cluster or PCM connector
  • Faulty instrument cluster
  • Failed lamp driver circuit in the PCM

Common misdiagnoses

  • Engine coolant temperature (ECT) sensor replaced even though this is a lamp output code, not a temperature signal code
  • Thermostat or cooling fan repairs performed for a nonexistent overheat
  • Water pump replaced on the assumption of an overheating condition
  • PCM replaced before checking the bulb and wiring

Troubleshooting steps

  1. 1.Confirm actual coolant temperature is normal

    Verify live ECT data reaches and holds normal operating temperature (roughly 85-105 C) to rule out a genuine overheat before treating this as a circuit fault.

  2. 2.Check the lamp during bulb test

    Cycle the key and watch whether the engine hot lamp illuminates during the cluster's prove-out sequence; no prove-out points to the bulb, cluster, or open circuit.

  3. 3.Command the lamp with a scan tool

    Use output control to toggle the hot lamp; correct response means the circuit is intact and the fault is intermittent.

  4. 4.Test the lamp control circuit

    With connectors disconnected, verify continuity through the circuit and confirm it is not shorted to ground (lamp always on) or open (lamp never on).

  5. 5.Isolate cluster versus PCM

    If the wiring is good, determine whether the cluster fails to respond to a good PCM command or the PCM driver never toggles, and replace the failed component.

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