What it means
The HV battery pack coolant pump B reports a underspeed condition. Battery thermal management may be impaired.
At a glance
- Usually lights the check-engine light
- The engine or gearbox may go into limp mode
How it works
Battery coolant pump B circulates coolant through part of a hybrid or electric vehicle’s high-voltage battery cooling system. This code sets when pump B runs slower than expected for its commanded operation, which can leave that part of the battery loop under-cooled.
Common causes
Most likely first.
- Pump wear or mechanical drag
- Low supply voltage
- Coolant flow restriction
Symptoms
- EV/hybrid system warning light on
- Reduced power output or limp mode
- Charging may fail or be slowed
- Reduced electric range
How to diagnose it
- Record freeze-frame data and check pump B’s commanded and reported speeds alongside battery temperatures with a compatible scan tool.
- Check coolant level and look for leaks or restrictions in the battery-cooling circuit using the vehicle’s specified procedure.
- Inspect pump B’s accessible low-voltage connector and wiring for a loose fit, corrosion, or damage without touching high-voltage components.
- Measure pump B supply and ground during commanded operation and compare them with the manufacturer’s specification.
- If supply and coolant flow are correct, test pump B for mechanical drag and verify its speed feedback using the manufacturer’s procedure.
Common fixes
- Restore the specified coolant level and repair any leak.
- Clear a confirmed restriction in the battery-cooling circuit.
- Repair a poor pump B electrical connection or damaged low-voltage wiring.
- Replace pump B if it remains below the required speed with correct supply and unobstructed flow.
Can I keep driving?
Avoid fast charging, hard acceleration, and long trips while the hybrid or EV warning is active; battery cooling may be reduced and the vehicle may limit power. Seek prompt diagnosis, and stop safely if a battery-temperature warning appears.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.