Powertrain
generic / SAE
P0128
Coolant Thermostat Below Regulating Temperature
The engine has been running long enough to reach operating temperature, but coolant temperature stayed below the thermostat's regulating value. Almost always caused by a thermostat stuck open. Costs fuel economy and increases cold-engine emissions.
SystemPowertrain
Typegeneric / SAE
GroupP0
Range / number1 / 28
Possible causes
- Thermostat stuck open high
- Coolant sensor reading low low
Inspection / repair
- Difficulty: medium
- DIY: possible
- Estimated cost: 50–350 €
- Estimated time: 0.7–3 h
- Component: thermostat
- Component: coolant temperature sensor
- MIL / check engine light
- emissions-relevant
- drive cycle required
Sources
References
sae:J2012