What it means
The control module detects a fault related to current in phase U of the electric/auxiliary transmission fluid pump motor.
At a glance
- Usually lights the check-engine light
- The engine or gearbox may go into limp mode
How it works
The electric or auxiliary transmission-fluid pump uses a motor with three phases, including phase U, to circulate fluid when the transmission needs it. P0B00 indicates that the control module detected a phase-U current fault, but the code alone does not say whether current was too low or too high.
Common causes
Most likely first.
- Pump motor or phase wiring fault
- Pump motor control or current-sensing fault
Symptoms
- Transmission or hybrid system warning light
- Transmission operation may be limited
How to diagnose it
- Save freeze-frame data and scan for transmission, pump, and hybrid-system codes to check whether the phase-U fault occurred with limited pump operation.
- Use live data to compare phase-U current with the other pump-motor phases under the conditions specified by the service information.
- Inspect the pump connector and phase-U wiring for loose terminals, corrosion, heat damage, or chafing.
- Check phase-U wiring continuity and isolation using the vehicle wiring diagram and the manufacturer's safety and test procedures.
- If the wiring is sound, test pump-motor operation and the control module's current-sensing circuit against the manufacturer's specifications.
Common fixes
- Repair a loose, corroded, or damaged pump connector or phase-U wire.
- Repair a verified phase-U circuit fault.
- Replace the pump motor if its phase operation fails the manufacturer's tests.
- Repair the current-sensing or pump-control circuit if testing identifies that fault.
Can I keep driving?
Avoid driving if transmission operation is limited, shifting becomes abnormal, or the vehicle enters limp mode; inadequate fluid circulation can lead to further transmission damage. If the vehicle still moves normally, restrict use and arrange prompt diagnosis.
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.