P026FCoolant Thermostat Performance
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- P026F is a general functional code for the coolant thermostat. CARB requires that the coolant reaches the temperature needed for other diagnostics in the approved time and comes within 11 °C of the thermostat's regulating temperature; from model years 2019–2021 petrol engines must also detect it dropping back below that temperature, and electric pumps or valves controlling coolant flow are monitored like a thermostat. The module follows coolant temperature against a heat model. No manufacturer using P026F was found – GM and Ford report thermostat faults as P0128, P01F0 or P2181 – so the description rests on CARB and the thermostat's function.
- What you may notice
- Check engine light on
- Slow warm-up, weak heating (stuck open)
- Low or fluctuating temperature gauge
- Overheating (stuck closed)
- Likely causes
- LikelyThermostat stuck open or opening too early
- PossibleThermostat stuck closed or opening too late
- PossibleMap-controlled thermostat: heating element or control faulty
- RareCoolant temperature sensor inaccurate
- RareLow coolant or air in the system
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €60 – €400
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.