P26C0Engine Coolant Bypass Valve D 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
- GM uses P26C0 for the block rotary valve, which controls coolant flow through the engine block between two mechanical end stops; its tables label it as the engine block coolant valve stuck open. The ECM counts a failure when requested and measured position differ by at least 10° while the raw feedback sits at 50° or more, i.e. on the open side. The 2019 L3B table grades it Type A, one trip; the 2025 table 25OBDG03B lowers the gap to 5° and grades it Type B. The check is suspended during the valve's calibration run and needs at least 11 V. GM bulletin 21-NA-149 lists P26C0 among codes caused by a chafed engine harness on 2019–2021 trucks. An open block valve lets the block stay cooler than intended, slowing warm-up.
- What you may notice
- Check engine light
- Longer warm-up, especially in cold weather
- Higher fuel consumption on short trips
- Likely causes
- LikelyBlock valve jammed on the open side
- PossibleChafed engine harness disturbing drive or feedback (GM 21-NA-149)
- RarePosition feedback reporting a wrong angle
- 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: €150 – €900
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.