P0B02

What it means

P0B02 means the control unit monitoring the electric auxiliary transmission fluid pump has detected too much current in the phase U winding of the pump's three-phase motor. The pump driver measured current above the permitted limit and set the code. The pump, its wiring, the driver or a mechanical load on the pump could all be responsible, and the layout varies by vehicle.

Symptoms

• Gearbox warning light or engine management light on
• Harsh, delayed or flared gear changes, especially after a stop-start restart
• Transmission in limp mode or restricted to certain gears
• Whining, buzzing or no noise from the auxiliary pump area
• Engine stop-start or hybrid/EV functions disabled
• Pump may cut out intermittently, mainly when the fluid is cold

Possible causes

• Wiring fault in phase U circuit: short to ground, short to another phase or to supply, or chafed insulationlikely
• Corroded, loose or damaged connector terminals at the pump or driverlikely
• Pump motor winding fault or internal shortpossible
• Pump mechanically stiff or seized from wear, debris or contaminated fluid, drawing excess currentpossible
• Incorrect, degraded or very cold, thick transmission fluid increasing the load on the pumppossible
• Fault in the pump driver or control module, including a power stage failurepossible
• Low or unstable supply voltage from a weak battery or charging fault upsetting the motor driverare

How to diagnose

1. Read all stored and pending codes and the freeze frame data, noting temperature, voltage and operating conditions when the fault set.
2. Check for other related codes, such as battery voltage, pump speed or communication faults, and address those first.
3. Check the transmission fluid level, condition and type against the manufacturer's specification, looking for burnt smell, metal debris or contamination.
4. Check battery condition and charging voltage, as low or unstable voltage can disturb motor drive.
5. Visually inspect the pump harness and connectors for chafing, heat damage, water ingress, corrosion and pushed-back pins.
6. Use a scan tool to command the pump if supported, and watch for commanded versus actual speed and current readings.
7. With the connector disconnected, test the phase windings for resistance balance and insulation to ground using the manufacturer's figures, which depend on the model.
8. Check the pump for free rotation or debris if it can be accessed, and follow the manufacturer's procedure for the driver or control module before condemning it.

How to fix

• Repair or replace damaged wiring and clean or replace corroded connectors in the phase U circuit.
• Replace the auxiliary pump assembly if the windings are faulty or the pump is seized or tight.
• Drain and refill with the correct specification fluid, and rectify any contamination source found.
• Replace the pump driver or control module if the checks prove it faulty, and complete any required programming or adaptation.
• Repair the battery or charging system if low voltage is found.
• Clear the code after the repair and road test to confirm it does not return.

Can I keep driving?

Nearby codes

• P0B01GenericElectric/Auxiliary Transmission Fluid Pump Motor Phase U Current Low
• P0B03GenericElectric/Auxiliary Transmission Fluid Pump Motor Phase V Current