Damaged wiring or connector on the phase U circuit to the pump motor (open circuit, short, chafing, corrosion or water ingress); Fault in the pump motor windings or a seized or worn pump drawing abnormal current; Fault in the pump driver or control module that supplies the motor phases; Low or degraded transmission fluid, or a blocked filter, putting abnormal load on the pump; Poor power supply or earth to the pump or its controller, including low system voltage; Internal fault in the transmission control unit; Outdated control unit software where the manufacturer has issued an update for this specific fault (model-specific).

P0B00

Electric/Auxiliary Transmission Fluid Pump Motor Phase U Current.

Generic
Powertrain
Generic code
Medium severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
B: AreaHybrid propulsion
00: FaultThe specific fault in that area

What it means

P0B00 means the control unit has found a problem with the current in phase U of the electric (auxiliary) transmission fluid pump motor. The pump is driven by a three-phase motor, and the controller monitors the current in each phase. If the phase U reading is outside the expected range or does not match the commanded pump operation, the code sets. The exact layout and trigger conditions vary by model and transmission.

Symptoms

Transmission or engine warning light on
Transmission in limp mode with limited gears or reduced performance
Harsh, delayed or flaring gear engagement, especially after a stop
Stop-start system not working or the engine stalling or hesitating when pulling away
Whining or buzzing from the pump, or no pump noise at all
Transmission temperature warning on in severe cases

Possible causes

Damaged wiring or connector on the phase U circuit to the pump motor (open circuit, short, chafing, corrosion or water ingress)likely
Fault in the pump motor windings or a seized or worn pump drawing abnormal currentlikely
Fault in the pump driver or control module that supplies the motor phasespossible
Low or degraded transmission fluid, or a blocked filter, putting abnormal load on the pumppossible
Poor power supply or earth to the pump or its controller, including low system voltagepossible
Internal fault in the transmission control unitrare
Outdated control unit software where the manufacturer has issued an update for this specific fault (model-specific)rare

How to diagnose

Read all stored and pending codes and the freeze frame data, noting temperature, voltage and vehicle state when the fault set
Check the transmission fluid level and condition using the manufacturer's procedure, as it varies by model
Visually inspect the pump wiring, connectors and any nearby harness routing for damage, heat, corrosion, moisture or loose pins
Check battery condition and charging voltage, then test the supply and earth feeds to the pump and its controller
Use live data, where available, to compare commanded pump speed with actual pump current or speed
Measure the resistance of the motor phase windings and their insulation to earth against the manufacturer's specification, with the circuit isolated
Check that the pump turns freely and quietly, following the model-specific access procedure
Check for service bulletins or available software updates for this model and code

How to fix

Repair or replace damaged wiring, terminals or connectors on the pump circuit
Replace the electric pump or pump motor if the windings are faulty or the pump is seized or worn
Replace or repair the pump driver or control module if the supply to the motor is confirmed faulty
Correct the fluid level, or service the fluid and filter as the manufacturer specifies, and fix the cause of any loss or contamination
Repair charging, battery or earth faults that cause low or unstable voltage
Update the control unit software only if the manufacturer lists it as a fix for this fault, then clear the code and road test

Can I keep driving?

Medium severity

The car may be driveable in limp mode, but low fluid pressure or an unreliable pump can cause poor shifting, overheating and transmission damage. Have it checked soon and avoid heavy loads or long journeys until it is repaired.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.