P0BF9: Drive Motor B Phase W Current Sensor Circuit

What it means

The current sensor for drive motor B phase W reports a circuit fault. Phase current measurement is unreliable.

At a glance

• Usually lights the check-engine light
• The engine or gearbox may go into limp mode

How it works

Drive motor B’s phase W current sensor measures current in the W phase for the hybrid or EV control module. This circuit code sets when the module detects a fault in that phase W sensor circuit, so it can no longer rely on the measurement; a failed sensor or wiring problem are likely causes.

Common causes

Most likely first.

1. Current sensor failed
2. Wiring fault

Symptoms

• EV/hybrid system warning light on
• Reduced motor power or torque
• Possible limp mode or vehicle shutdown

How to diagnose it

1. Save freeze-frame data and check live phase U, V and W readings for missing or implausible phase W data.
2. With the vehicle powered down as directed by the manufacturer’s high-voltage safety procedure, inspect the phase W sensor connector and harness for damage, loose pins or contamination.
3. Check phase W sensor power, ground, signal wiring and connector continuity against the manufacturer’s specification.
4. Compare the phase W sensor signal with phases U and V during the manufacturer’s specified test to narrow down a sensor versus wiring fault.
5. If the circuit checks pass, test the phase W sensor and control module input using the manufacturer’s diagnostic procedure.

Common fixes

• Clean and reseat the phase W sensor connector if contact is poor.
• Repair damaged or loose phase W sensor wiring or terminals.
• Restore a faulty phase W sensor ground or power connection if identified by testing.
• Replace the phase W current sensor if it fails its prescribed test.
• Repair or replace the control module only if its input is confirmed defective.

Can I keep driving?

Reduced torque, limp mode or shutdown may occur if the module cannot trust the phase W reading. Avoid driving if power is limited or the vehicle behaves unpredictably, as propulsion could be lost.