U01BCLost Communication With Charge Air Cooler Coolant Pump B
- Generic OBD-II code · Network
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- Engines with a water-cooled charge air cooler run a separate low-temperature coolant loop with an electric pump, usually a LIN slave of the engine controller. Rheinmetall's pumps of this kind are driven via PWM or LIN, and Bosch's PCE pump has a built-in diagnostic function reported to a higher-level unit. U01BC applies where a second pump, B, serves this loop. No manufacturer documents the code publicly. For pump A, GM's 2025 tables (25OBDG04B) declare lost LIN contact after 2.5 s without a pump response while the pump is enabled, Type A, one trip, a sign of how strictly such losses are treated. CARB 1968.2 requires charge air undercooling to be detected, which a silent pump would hide. Expect a MIL and reduced boost or power when hot; U02A9 is pump A.
- What you may notice
- MIL on
- Reduced power or boost, especially in hot weather
- Likely causes
- LikelyWater or corrosion in the pump connector at the front of the engine bay
- PossiblePump supply fuse or relay open
- PossibleElectric coolant pump B electronics or motor 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: €0 – €700
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.