What does code P0128 mean on a Mercedes-Benz and is it safe to drive?
P0128: Coolant Thermostat (Coolant Temp Below Thermostat Regulating Temperature). Here's what it means on your Mercedes-Benz, what usually causes it, what repairs typically cost, and how safe it is to keep driving.
What this code means
The engine is not reaching normal operating temperature in the expected time. Usually a stuck-open thermostat.
Common causes for your Mercedes-Benz
- Thermostat stuck open
- Coolant temperature sensor fault
- Low coolant level
Symptoms
- Check Engine Light
- Heater may blow cold
- Poor fuel economy
- Temperature gauge stays low
Typical fixes
- Replace thermostat
- Replace coolant temperature sensor if faulty
- Refill coolant and check for leaks
Repair cost range
For a Mercedes-Benz, repairs for P0128 often fall between $100 and $350, depending on the cause and whether you use OEM or aftermarket parts. Labor rates vary by location.
Known issues on Mercedes-Benz
Mercedes P0128 on M272 V6 and OM642 V6 diesel engines is unusual. On petrol models, a sticking thermostat is the cause; on diesels, a thermostat bypass valve issue is also possible. Use OEM Mercedes thermostats for best results.
Most commonly affected models