What it means
The motor electronics coolant pump B control circuit reports a control circuit high condition. Power electronics cooling cannot be commanded reliably on branch B.
At a glance
- Usually lights the check-engine light
- The engine or gearbox may go into limp mode
How it works
Pump B circulates coolant through the hybrid or EV power electronics. The control module monitors the pump's control circuit and sets P0B3A when the circuit signal is higher than expected, such as when the control wire is connected to battery positive or the pump circuit is open.
Common causes
Most likely first.
- Control wire shorted to B+
- Open pump motor
- Connector pins corroded - high contact resistance
Symptoms
- Hybrid-system warning light may illuminate
- Reduced power or limited hybrid operation
- Power electronics may overheat or trigger protective shutdown
How to diagnose it
- Record freeze-frame data and check scan-tool pump B command and status to determine when the high circuit reading occurred.
- Inspect the pump B harness for damaged insulation or contact with a power feed that could short the control wire to B+.
- Check the connector for corrosion, loose pins, or a backed-out terminal that could leave the circuit open or disrupt its signal.
- Using the manufacturer's high-voltage safety procedure, test the control wire for a short to B+ and check continuity through the circuit against the manufacturer's specification.
- Test pump B for an open motor circuit, then test the controller output if the wiring and pump pass.
Common fixes
- Repair pump B control wiring shorted to battery positive.
- Restore the connector terminal fit and repair corroded or damaged pins.
- Replace pump B if its motor circuit is open.
- Repair the controller connection or output if testing identifies it as the cause.
Can I keep driving?
Keep driving to a minimum because pump B may not circulate coolant and power electronics can overheat, prompting reduced power or shutdown. Avoid heavy loads and stop safely if an overheating warning or power limitation occurs.
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.