P0655
Engine Hot Lamp Output Control Circuit.
- Generic
- Powertrain
- Generic code
- Medium severity
How this code is built
- P
- SystemPowertrain
- 0
- Defined bySAE, the same on every car
- 6
- AreaComputer and output circuits
- 55
- FaultThe specific fault in that area
What it means
P0655 is the generic code for a fault in the engine hot lamp output control circuit. The engine control unit drives a warning lamp that tells the driver the engine is overheating, and it has detected that the lamp circuit is not behaving as commanded, for example an open circuit, a short to earth or a short to voltage. The code points to the lamp circuit itself rather than to the engine actually being too hot, though the two should not be assumed unrelated until checked.
Symptoms
- Engine hot or temperature warning lamp stays on, or never lights
- Warning lamp does not perform its bulb check at ignition on
- Malfunction indicator lamp may be illuminated
- Temperature gauge reading may disagree with the warning lamp
- Other warning lamps or instrument cluster functions behaving oddly
Possible causes
- Damaged, chafed or corroded wiring between the control unit and the instrument cluster or lamplikely
- Poor connection or corroded terminals at the control unit or instrument cluster connectorslikely
- Faulty instrument cluster or failed lamp driver or bulb circuitpossible
- Short to earth or to voltage in the lamp control wirepossible
- Fault in the engine control unit output driverrare
- Outdated control unit or cluster software on a model with a known issuerare
How to diagnose
- Read all stored codes and freeze frame data, and note any coolant temperature or other cooling system codes
- Check whether the engine hot lamp performs its bulb check at ignition on and compare with the actual coolant temperature on the gauge and live data
- Confirm the engine is not actually overheating by checking coolant level, fan operation and live coolant temperature
- Visually inspect the wiring and connectors between the control unit and instrument cluster for chafing, water ingress, corrosion and pushed-out pins
- Check battery condition and charging voltage, as low or unstable voltage can cause spurious circuit faults
- Using the wiring diagram for the specific model, test the lamp control wire for continuity, short to earth and short to voltage
- Check the cluster supply, earth and lamp circuit, and test the output with a command from the diagnostic software if the model supports it
- Check for applicable service bulletins or software updates for the specific vehicle
How to fix
- Repair or replace damaged wiring and restore insulation or routing
- Clean, repair or replace corroded or loose connector terminals
- Repair or replace the instrument cluster or lamp driver if the fault is confirmed there
- Replace the engine control unit only after wiring and cluster have been proven good and the output fault is confirmed
- Apply a manufacturer software update if an outdated calibration is a known cause for that model
- Clear the code and road test to confirm the fault does not return
Can I keep driving?
The car can usually be driven for a short time, but the engine hot warning may not work, so watch the temperature gauge closely and have it fixed soon. If the gauge reads high or you see steam or coolant loss, stop and let the engine cool.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.