Since model years 2019–2021 CARB requires petrol engines to detect a thermostat fault not only during warm-up but also when the coolant, after reaching operating temperature, drops back below the temperature needed for other diagnostics. P01F0 is this check. GM sets it when coolant falls below 64 °C with a conventional thermostat or 70.5 °C with an electrically heated one (2019 Corvette: 65/78.5 °C) after having been above it, with at least 0.8 km driven, ambient above −7 °C, enough heat input and no long overrun downhill; two trips. GM also uses it on the 6.6 litre Duramax diesel as a 'stuck open thermostat' check. Ford does not use the code in the documents checked. Usual cause is a thermostat stuck open.
Medium severity. Can I keep driving?Watch the temperature gauge. If it climbs or a warning appears, stop the car in a safe place and turn off the engine: overheating can cause serious damage.
Symptoms
- Check engine light on (after two drive cycles)
- Temperature gauge drops while driving
- Weak cabin heating, higher consumption
Most likely causes
- Thermostat stuck open or not sealing
- Heated map thermostat, thermal management valve or switchable water pump faulty
- Radiator fan running constantly (relay stuck)
- Coolant sensor drifting cold
- Low coolant or air in the system
What to check, in order
Start with the simplest. You can tick off each step.
Good to know
- Repair difficulty: medium
- It affects emissions.
What each character of P01F0 means
- P: Powertrain: engine and transmission
- 0: Generic code: same on every make
- 1: Air and fuel
- F0: Specific fault in that system
Frequently asked questions
Can I keep driving with code P01F0?
Watch the temperature gauge. If it climbs or a warning appears, stop the car in a safe place and turn off the engine: overheating can cause serious damage.
What causes code P01F0?
The most common causes are: thermostat stuck open or not sealing; heated map thermostat, thermal management valve or switchable water pump faulty; radiator fan running constantly (relay stuck).
Related codes
- P0128Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)
- P0125Insufficient Coolant Temperature for Closed Loop Fuel Control
- P0116Engine Coolant Temperature Sensor 1 Circuit Range/Performance
- P0597Thermostat Heater Control Circuit/Open
- P01E4Engine Coolant Temperature Sensor 3 Circuit Range/Performance
Sources
- law.cornell.edu: 13 CCR 1968.2
- gsi.ext.gm.com: 18OBDG04 Engine Diagnostics
- gsi.ext.gm.com: 19OBDG03A Diagnostics
- gsi.ext.gm.com: 14OBDG10 Engine Diagnostics
Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.