What it means
A circuit fault on the engine-hot warning lamp output - the high-coolant-temperature warning may not light when needed.
At a glance
- Usually lights the check-engine light
How it works
The engine control module controls an output circuit for the engine-hot warning lamp, which alerts the driver to excessive coolant temperature. P0655 sets when that lamp-control circuit does not behave as expected, so the warning may fail to illuminate when the engine overheats.
Common causes
Most likely first.
- Open or short in the warning lamp output wiring
- Faulty engine-hot warning lamp or instrument cluster
- Poor connector contact
- Control module output fault
Symptoms
- Check engine light on
- Possible limp mode or no-start
- Multiple follow-up faults across modules
- Reset/relearn may be needed after repair
How to diagnose it
- Check freeze-frame data and scan for coolant-temperature or instrument-cluster codes that may point to a shared wiring or control problem.
- With the ignition on, verify through the vehicle's lamp test or scan-tool output control that the engine-hot warning indicator can illuminate.
- Inspect the warning-lamp output wiring and connectors for opens, shorts, corrosion, or loose and pushed-back pins.
- Use the wiring diagram to test continuity and shorts in the output circuit, and check the lamp or cluster input against the manufacturer's specification.
- If wiring and the cluster pass, test the control module's lamp output using the manufacturer's procedure.
Common fixes
- Repair an open or shorted warning-lamp output wire.
- Clean or repair a poor connector contact.
- Repair the warning indicator or instrument cluster if its input or lamp test fails.
- Repair or replace the control module only after the output circuit has been verified.
Can I keep driving?
The vehicle may drive normally, but you could miss an engine-hot warning and continue driving while coolant temperature is dangerously high. Watch the temperature gauge closely and stop safely if temperature rises or steam appears; overheating can damage the engine quickly.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.