P2B28: Hybrid/EV Battery Pack Coolant Pump A Performance
What to do
Drivable — expect reduced power, gentler charging and weaker regeneration while the pack protects itself. Avoid rapid charging until it is repaired; that is the biggest heat event the battery has and the one its cooling now cannot cover. If the coolant loop was recently worked on, have it bled properly before any parts are replaced — air in the loop reproduces every symptom of a failed pump.
What this code means
Hybrid/EV battery pack coolant pump A is not performing as commanded.
The traction battery has its own liquid cooling in many designs, and this pump moves it. Battery cells live inside a narrow temperature window — too hot ages them permanently, too cold limits what they can safely deliver — so the pack circulates its own coolant, driven by an electric pump the module speed-controls to match the thermal load of driving and charging.
A pump fault turns into a battery limitation almost immediately. The module protects the pack it can no longer cool: reduced power, reduced regenerative braking, slower charging, and on hot days a car that feels artificially gentle. Rapid charging suffers first, because it is the biggest heat event the pack ever has.
Check the simple hydraulics before the pump. A low loop or air from a poorly bled repair makes a healthy pump misbehave — running fast against nothing, cavitating, moving too little heat. The pump's own electronics report speed and load precisely, which is how the module tells a jammed rotor from an empty loop from a tired motor.
Likely causes
Start here
- Faulty electric coolant pump · specialist
- Air trapped in the inverter cooling circuit · moderate
- Low coolant level · easy
Less common
- Corroded or loose connector · specialist
Symptoms
Components involved
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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