P26BBEngine Coolant Bypass Valve C Range/Performance
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- Needs a drive cycle to confirm a fix
- How the car detects it
- P26BB is GM's main functional code for its rotary coolant flow control valve. The ECM compares commanded and measured angle; a gap above 12° after the target has settled, or movement slower than calibrated, counts as a fault. In the 2019 L3B table this is Type A (4 of 5 s), in the 2025 diesel table Type B (8 of 10 s). Several GM bulletins concern it: 21-NA-256 (2019–2022 engines LSY, L3B, L3T) blames a break-in phase of the valve under about 2,000 miles and calls for a new valve only on repeat; 20-NA-100 (2.7L L3B pickups 2019–2020) and 22-NA-082 (3.0L diesel 2020–2022) prescribe new ECM software; PIE0697 gathered field data on the diesel with P2B60. A sluggish valve can let the engine run too warm or too cool.
- What you may notice
- Check engine light
- Coolant temperature higher or lower than normal
- Code may disappear after further driving on a new valve
- Likely causes
- LikelyNew valve still in its break-in phase (GM, low mileage)
- PossibleECM calibration needing an update per GM bulletin
- PossibleValve or actuator sticking or worn
- RareInaccurate valve position feedback
- 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: €0 – €900
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.