P26B8Engine Coolant Bypass Valve C Control Circuit Low
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- How the car detects it
- With P26B8 a drive line of valve C is pulled toward ground. The best public description comes from GM's 2025 ECM table 25OBDG04B for the six-cylinder diesel: valve C sits on an H-bridge, and the controller looks for a grounded line separately in the opening and the closing direction, each time only while the other direction is free of the same fault. The result is a Type B code, so the lamp normally lights on the second trip. GM bulletin 21-NA-149 lists P26B8 among many codes that a chafed engine harness can trigger on 2019–2021 trucks and SUVs with gasoline V6/V8, 2.7L turbo or 3.0L diesel engines. Ford has no separate low code here. A grounded line can stall the valve or blow the driver, leaving engine temperature less well controlled.
- What you may notice
- Check engine light after two trips
- Unstable or high coolant temperature
- Further valve or harness codes stored at the same time
- Likely causes
- LikelyDrive wire chafed against the engine or body and shorted to ground
- PossibleInternal short in the valve C motor
- RareWater or coolant in the valve connector
- 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: €60 – €650
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.