P26AFEngine Coolant Bypass Valve 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
- P26AF is the functional fault for valve B remaining open against its command. No manufacturer documents this code publicly; Ford, for instance, monitors its valve B (transmission cooling) only electrically through P26AC/P26AE. How an open-stuck check can work is shown by Ford's hybrid logic for P26AB on valve A, which compares two coolant temperatures for 60 s after the valve should have changed state. CARB requires output components to be checked for proper functional response where feasible. A valve stuck open on an auxiliary coolant path wastes heat during warm-up, so the engine or transmission takes longer to reach temperature; causes include deposits, a broken return spring or gear, or a seized actuator.
- What you may notice
- Check engine light
- Longer warm-up, higher fuel use on short trips
- Lower cabin heat in cold weather
- Likely causes
- LikelyValve held open by deposits or debris
- PossibleSeized actuator or broken drive gear
- RareCoolant temperature sensor bias misleading the check
- 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: €100 – €800
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.