Diagnostic Trouble Code
P0128 — Coolant Thermostat Below Regulating Temp
Coolant Thermostat Below Regulating Temp
Definition
The engine coolant has not reached the expected temperature within a specified time after starting. The ECM monitors coolant temperature to manage fuel enrichment, emissions controls, and transmission shift strategy.
Common Causes
- Stuck-open thermostat
- Faulty engine coolant temperature (ECT) sensor
- Low coolant level
- Cooling fan running continuously due to a relay fault