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U01BC Lost Communication With Charge Air Cooler Coolant Pump B

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

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.

Likely causes

Water or corrosion in the pump connector at the front of the engine bay
Pump supply fuse or relay open
Electric coolant pump B electronics or motor faulty

Symptoms

  • MIL on
  • Reduced power or boost, especially in hot weather

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€0–700
Time0.5–3 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

cac coolant pump blin bus

Related codes

U02A9U05AAU0100

References: gsi.ext.gm.com, law.cornell.edu, rheinmetall.com, bosch-mobility.com.