What it means
The control module detects phase V current below the expected level in 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
Phase V is one of the three electrical phases driving the electric or auxiliary transmission-fluid pump. P0B04 sets when the control module sees phase-V current below its expected level, often because an open or high-resistance phase-V connection reduces current to the motor.
Common causes
Most likely first.
- Open or high-resistance phase wiring
- Pump motor fault
- Current sensing or control fault
Symptoms
- Transmission or hybrid system warning light
- Transmission operation may be limited
How to diagnose it
- Review freeze-frame data and related transmission or pump codes to see when phase-V current dropped.
- Compare live phase-V current with phases U and W during the manufacturer's specified pump test conditions.
- Inspect the phase-V wire and pump connector for an open, poor terminal contact, corrosion, or heat damage.
- Measure phase-V continuity and voltage drop according to the wiring diagram and manufacturer's specifications.
- If the circuit is sound, test the pump motor and current-sensing or control circuit for a fault causing the low reading.
Common fixes
- Reseat or clean the pump connector if a poor connection is found.
- Repair an open or high-resistance phase-V wire or terminal.
- Replace the pump motor if its phase-V current remains low and it fails testing.
- Repair the current-sensing or control circuit if it is producing the low reading.
Can I keep driving?
Restrict driving if the transmission or hybrid system limits operation, since low phase-V current may reduce fluid-pump output. Stop if shifting becomes abnormal or the vehicle enters limp mode.
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.