Powertrain, generic (extended)

P2B2A Hybrid/EV Electronics Coolant Pump A Overspeed - Dry Run

Check engine lightUsually off
EmissionsRelevant
Drive cycleNot required
Limp modePossible

The pump in the low-temperature loop that cools power electronics and often the drive unit reports that it is turning too fast for its load, the sign of air instead of coolant. Mercedes documents P2B2A7A in the powertrain control unit of the 167 series (GLE/GLS) with M177 V8 and 48 V system before model year 2024: the 15 W pump beside the transmission switches to an emergency dry-run mode when the circuit holds air, the cluster shows a yellow coolant message; the fix is vacuum filling and staged venting with XENTRY, plus pumps of the correct part number. Audi logs P2B2A00 in thermal management 00C5 of the 2023–2024 e-tron and Q8 e-tron, with P0CE900 and low coolant, and replaces a damaged hose. Battery pump A has the equivalent P2B29.

Likely causes

Air in the low-temperature circuit after filling or a leak
Damaged or leaking coolant hose (Audi e-tron)
Pumps of the wrong part number or position (Mercedes 167)

Symptoms

  • Coolant or drive system warning in the instrument cluster
  • Churning noise from the affected pump
  • Reduced drive power until the loop is bled

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€80–800
Time0.5–3 h

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

Parts involved

hybrid electronics coolant pump apower electronics coolant loop

Related codes

P2E46P0CEAP0CE9P2C67P2B29

References: static.nhtsa.gov, static.nhtsa.gov, static.nhtsa.gov, law.cornell.edu.