P2CF1Auxiliary Thermostat B Stuck Open
- 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
- P2CF1 covers a further auxiliary thermostat, labelled B, that stays open, so its loop loses its warm-up phase and runs below the intended temperature. Which loop B controls is the maker's choice: engines with split cooling may regulate head, block, oil or heater flow with separate thermostats, each needing its own temperature sensor for diagnosis. No manufacturer documents P2CF1 publicly, and the only published auxiliary thermostat case, Lotus bulletin 131-26007, concerns thermostat A (P2CEF). CARB demands that the OBD system detect a thermostat that keeps coolant from reaching its regulating temperature and, for gasoline vehicles from 2019–2021, one that lets it drop again; for multiple thermostats it asks for an approved plan. Fuel use and heater output suffer.
- What you may notice
- Engine warning lamp
- Slow warm-up and higher fuel use in cold weather
- Weaker cabin heating
- Likely causes
- LikelyValve held open by debris or a weak return spring
- PossibleWorn wax element that no longer retracts fully
- RareTemperature sensor of that loop reading too low and faking the fault
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Usually a job for a workshop.Typical cost: €120 – €800
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.