OBD codes / P0128
P0128
ModerateCoolant Thermostat Below Regulating Temperature
Get it looked at soon to avoid further wear.
Likely causes
- stuck-open thermostat
- low coolant
- faulty coolant temp sensor
Common fixes
- replace thermostat
- top up coolant
Seeing P0128 on your car? Get a diagnosis specific to your exact year, make and model.
Diagnose P0128 for my vehicleGeneric OBD-II reference. Manufacturer-specific behavior varies — confirm with a scan tool and, for safety-related codes, a professional inspection.