U02BA: Lost Communication With Hybrid/EV Electronics Coolant Pump B

What it means

The vehicle bus reports loss of communication with the hybrid/EV power-electronics coolant pump B. Inverters and DC/DC stages on this loop lose active cooling and may derate.

At a glance

• Usually lights the warning light of the system that lost communication
• The engine or gearbox may go into limp mode

How it works

Hybrid or EV power-electronics coolant pump B circulates coolant through the assigned inverter, DC/DC converter or related components. The vehicle network monitors messages from the pump's control electronics and sets this code when pump B stops communicating. Cooling on that loop may be reduced, prompting power derating or shutdown to protect components.

Common causes

Most likely first.

1. Bus wiring open or shorted
2. Module without power or ground
3. Module failed

Symptoms

• Multiple warning lights may illuminate
• Affected modules may go into limp mode or shut down
• Specific functions inoperative depending on module
• Diagnostic tools may show communication faults

How to diagnose it

1. Scan all modules and save freeze-frame data, especially power-electronics temperatures and related pump or network faults, before clearing anything.
2. Use live data to check whether pump B reports status or commanded operation and whether temperatures on its cooling loop are rising.
3. With the vehicle made safe according to its high-voltage service procedures, inspect pump B's low-voltage connector and bus wiring for damage, corrosion or coolant intrusion.
4. Check the pump's specified power and ground using the manufacturer's service information; do not probe high-voltage circuits as part of this check.
5. Test the communication wiring to pump B for opens, shorts or poor connections using the manufacturer's network procedure.
6. If the supply and bus checks pass, follow the manufacturer's procedure to test pump B and confirm coolant flow and communication after repair.

Common fixes

• Repair a loose, corroded or coolant-contaminated connector at pump B.
• Repair damaged communication wiring or restore the pump's specified low-voltage power or ground.
• Replace pump B if testing confirms its electronics or pump assembly has failed.
• Bleed or refill the affected coolant loop as required after pump or hose work, then verify temperatures and operation.

Can I keep driving?

Avoid driving if a hybrid or EV warning, reduced-power message or rising temperature appears; stop safely and follow the vehicle's instructions because inverter or DC/DC components can overheat without pump B. Even without a warning, limit use and arrange prompt diagnosis, since the vehicle may derate or shut down as temperatures rise.