P2B5CEngine Coolant Flow Control Valve Supply Circuit Low
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- How the car detects it
- With P2B5C the supply voltage reaching the driver of the coolant flow control valve motor is too low. GM monitors this on the 3.0-litre Duramax (25OBDG04B): if the motor driver sees less than 6 V while the powertrain relay delivers more than 11 V, the difference points at the feed path, and a Type B fault follows after 80 hits in 100 samples. Typical causes are a blown or loose fuse, a corroded relay contact or a damaged supply wire; 21-NA-149 includes P2B5C among the LM2 codes linked to a chafed harness. Without enough voltage the motor cannot position the valve, so engine temperature control falls back to a default. A weak battery alone rarely sets it, because the relay check would fail as well.
- What you may notice
- MIL on after two drives
- Valve does not move, temperature control in fallback mode
- Likely causes
- LikelyBlown or loose fuse, corroded relay contact in the valve feed
- PossibleSupply wire damaged or chafed in the engine harness
- RareHigh resistance at a ground or splice of the feed circuit
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €10 – €400
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.