The coolant-temperature signal is implausible relative to other data (e.g. doesn't track warm-up correctly). On the flat-six this is often a failing ECT sensor but can also flag a thermostat problem. A bad ECT signal skews cold-start enrichment and fan control.
SYMPTOMS
- Check-engine light
- Cooling-fan or gauge anomalies
- Poor cold-start / economy
- Erratic temperature reading
LIKELY CAUSES
- Failing ECT sensor
- Wiring/connector fault
- Thermostat fault affecting warm-up
- Low coolant
DIAGNOSIS STEPS
- Compare ECT vs intake-air temp at cold start (should match)
- Watch ECT track smoothly during warm-up
- Check wiring/connector
- Verify coolant level and thermostat operation
RELATED PARTS
- Engine coolant temperature sensor
- Thermostat