Powertrain, generic (extended)

P2CB1 Charge Air Cooler Coolant Pump B Overspeed/Air In System

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P2CB1 means pump B in the charge air cooling loop turns faster than it should. An electric pump loses its hydraulic load when the impeller churns air instead of coolant, so overspeed is mostly a symptom of a low level or poor bleeding. No manufacturer documents P2CB1 publicly. For pump A (P2B83), GM's 2025 diesel table 25OBDG04B treats 8,500 rpm or more in 8 of 10 one-second samples as a fault, at 11 V or higher, Type B with MIL after two trips. GM's LT4 bulletin 18-NA-291 adds that this kind of pump shuts itself off once it draws air, which is why the loop there has to be vacuum filled. Check level, leaks that suck in air, and the bleed procedure before replacing pump B. If the pump then overheats, P2CB5 may follow.

Likely causes

Air trapped in the loop after service or incomplete bleeding
Low coolant from a leak in the charge air cooler circuit
Impeller loose or broken on the shaft of pump B

Symptoms

  • MIL on after two trips
  • Gurgling or a high-pitched pump noise
  • Low coolant warning or falling expansion tank level

Repair estimate

DifficultyMediumDIY possible
Parts and labour€20–700
Time0.5–3 h

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

Parts involved

cac coolant pump bcac coolant loop

Related codes

P2B83P2CB2P2CB0P2CB5U01BC

References: law.cornell.edu, gsi.ext.gm.com, static.nhtsa.gov.