What does code P0128 mean on a Jeep and is it safe to drive?
P0128: Coolant Thermostat (Coolant Temp Below Thermostat Regulating Temperature). Here's what it means on your Jeep, 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 Jeep
- 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 Jeep, 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 Jeep
Jeep P0128 on 3.7L and 3.6L Pentastar V6 engines is a standard thermostat replacement job. The Pentastar thermostat housing is known to leak at the gasket when the thermostat is replaced—replace both.
Most commonly affected models
Grand Cherokee 2005–2010Liberty 2002–2007Cherokee 2014–2019