The engine has not reached a coolant temperature high enough to enter closed-loop fuel control in the expected time.
SYMPTOMS
- Check-engine light
- Long warm-up
- Worse cold-running economy
LIKELY CAUSES
- Thermostat stuck open
- Faulty ECT sensor
- Low coolant level
DIAGNOSIS STEPS
- Monitor the warm-up curve in live data
- Verify coolant level
- Test thermostat operation
- Verify ECT sensor against IAT at cold start
RELATED PARTS
- Thermostat
- ECT sensor