P2B2A: Hybrid/EV Electronics Coolant Pump A Overspeed

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.

High severity. Can I keep driving?If the car still runs, drive as little as possible and go to a specialized repair shop. Do not touch the orange cables: they carry high voltage.

Symptoms

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

Most 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)

What to check, in order

Start with the simplest. You can tick off each step.

Read the codes with a hybrid-compatible scanner and write down the freeze frame data
Make sure the battery cooling air intake is clean
Check the 12 V auxiliary battery, which can also trigger warnings
Leave any high-voltage measurements to a specialized repair shop

Good to know

Repair difficulty: medium
It can trigger limp mode.
It affects emissions.

What each character of P2B2A means

P: Powertrain: engine and transmission
2: Generic code: same on every make
B: Subsystem depends on the code range
2A: Specific fault in that system

Frequently asked questions

Can I keep driving with code P2B2A?

If the car still runs, drive as little as possible and go to a specialized repair shop. Do not touch the orange cables: they carry high voltage.

What causes code P2B2A?

The most common causes are: 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).

Related codes

Sources

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.

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