OBD2 fault code

P0128 Coolant thermostat (coolant temperature below thermostat regulating temperature)

Medium priorityPowertrain (P)Generic code (SAE)

The engine takes too long to warm up. The coolant does not reach its normal operating temperature of about 90°C. The most common cause is a seized, open thermostat. Fuel consumption rises, and in winter the cabin heats up more slowly.

Most common causes of P0128

1Seized, open thermostat (most common)
2Faulty coolant temperature sensor
3Low coolant level in the system

Can I keep driving?

Visit a garage within 1 to 2 weeks. Replacing the thermostat is inexpensive, and driving for long periods can damage the catalytic converter.

P0128 by manufacturer

Manufacturer-specific codes can mean something different depending on the make.

Audi

Defective engine thermostat, defective engine coolant temperature sensor, defective intake air temperature sensor, defective cooling system, low engine coolant, dirty engine coolant causing incorrect coolant temperature sensor readings, defective or always running engine cooling fan(s)

P0128 – frequently asked questions

What does fault code P0128 mean?+

P0128 means: Coolant thermostat (coolant temperature below thermostat regulating temperature). The engine takes too long to warm up. The coolant does not reach its normal operating temperature of about 90°C. The most common cause is a seized, open thermostat. Fuel consumption rises, and in winter the cabin heats up more slowly.

What are the most common causes of P0128?+

Seized, open thermostat (most common); Faulty coolant temperature sensor; Low coolant level in the system.

Can I drive with fault code P0128?+