What does code P0128 mean on a Mitsubishi and is it safe to drive?
P0128: Coolant Thermostat (Coolant Temp Below Thermostat Regulating Temperature). Here's what it means on your Mitsubishi, what usually causes it, what repairs typically cost, and how safe it is 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 for your Mitsubishi
- 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 Mitsubishi, 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 Mitsubishi
Mitsubishi P0128 on 4B11 and 6G74 engines is typically a failed thermostat. OEM Mitsubishi thermostats are recommended; aftermarket units sometimes fail prematurely on these cooling systems.
Most commonly affected models
Outlander 2007–2013Lancer 2008–2015Eclipse 2006–2012