2020 Mercedes-Benz P0128: What It Means & Is It Safe to Drive?
P0128 on the 2020 Mercedes-Benz: Coolant Thermostat (Coolant Temp Below Thermostat Regulating Temperature). Here's what it means, what usually causes it, what repairs typically cost, and whether it's safe to keep driving.
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What this code means
The engine is not reaching normal operating temperature in the expected time. Usually a stuck-open thermostat.
Common causes on the 2020 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 2020 Mercedes-Benz, repairs for P0128 typically fall between $100 and $350, depending on the root cause and labor rates in your area.
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
C300 2008–2014E350 2010–2015ML350 2012–2015