P2B5BEngine Coolant Flow Control Valve Control Circuit High
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- How the car detects it
- P2B5B covers a short to battery voltage on the motor leads of the coolant flow control valve. GM's diesel table 25OBDG04B evaluates it through the driver stage as well: a current above 9 A with a lead tied to supply counts as a failure, and the usual 80-of-100 rule with 12.5 ms sampling stores a Type B code. GM bulletin 21-NA-149 names P2B5B in its LM2 harness-chafing condition together with blown fuses and rough running, which points at wiring rubbing on powered circuits rather than at the valve. Because the driver shuts down to protect itself, the valve no longer reacts and warm-up control is lost. Ground short and open are P2B5A and P2B59.
- What you may notice
- MIL on after two drives, possibly further codes from the same harness
- Blown fuses or rough running if the harness is chafed
- Weak heater output during warm-up
- Likely causes
- LikelyMotor lead chafed against a powered circuit (GM LM2, 21-NA-149)
- PossibleCorroded or wet connector bridging to supply
- RareDriver stage in the engine control module faulty
- 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 – €1,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.