P0B03

What it means

P0B03 means the control unit has detected a fault with the current in phase V of the electric or auxiliary transmission fluid pump motor. The pump is driven by a three-phase motor, and the module saw phase V current outside the expected range or not matching what it commanded. The exact setting conditions and the pump's role depend on the vehicle, so check the manufacturer's data for the model.

Symptoms

• Warning light on, possibly with a transmission or hybrid system warning message
• Delayed or harsh gear engagement, especially after a stop-start event or from cold
• Gearbox going into a limited-performance or limp mode
• Whining, buzzing or no audible pump noise from the transmission area
• Stop-start system or hybrid functions disabled or behaving erratically

Possible causes

• Wiring or connector fault in the pump motor phase V circuit (open circuit, high resistance, short or corrosion)likely
• Worn, overheated or failing pump motor with an internal winding faultlikely
• Faulty pump motor driver or control modulepossible
• Pump mechanically stiff or seized due to contaminated, degraded or low transmission fluid, drawing abnormal currentpossible
• Low or unstable supply voltage from a weak battery or poor power and earth connectionspossible
• Outdated or faulty control software, where the manufacturer has identified it as a causerare

How to diagnose

1. Read all stored and pending codes and the freeze frame data, noting voltage, temperature and vehicle state when the code set, and check for related transmission or power supply codes.
2. Check the manufacturer's information for how this pump is used on the model and for any known issues or service bulletins.
3. Check transmission fluid level and condition using the correct procedure for the vehicle, looking for burnt smell, debris or contamination.
4. Visually inspect the pump harness and connectors for chafing, heat damage, water ingress, corrosion and bent or pushed-back pins.
5. Test battery condition and check the supply and earth voltage drops at the pump and its controller.
6. With the circuit isolated, measure the resistance of the motor windings and the wiring between pump and controller, comparing phases against each other and against specification.
7. Use a scope or the scan tool's live data to check that the pump is commanded and that the phase currents are balanced and plausible while it runs.
8. If the wiring and motor test good, suspect the controller and confirm its output and software status per manufacturer procedure.

How to fix

• Repair or replace damaged wiring, terminals or connectors in the phase V circuit.
• Replace the electric transmission fluid pump or motor if the windings are faulty or the pump is seized.
• Replace the pump controller or driver module if it is confirmed faulty.
• Correct the fluid level and replace contaminated fluid, and investigate the source of any contamination.
• Restore proper power and earth supply by replacing a weak battery or repairing poor connections.
• Apply a manufacturer software update only if a bulletin identifies outdated calibration as the cause.

Can I keep driving?

Nearby codes

• P0B02GenericElectric/Auxiliary Transmission Fluid Pump Motor Phase U Current High
• P0B04GenericElectric/Auxiliary Transmission Fluid Pump Motor Phase V Current Low