What it means
The auxiliary transmission fluid pump phase U-V-W output reports a circuit/open condition.
At a glance
- Usually lights the check-engine light
- The engine or gearbox may go into limp mode
How it works
The auxiliary transmission fluid pump uses a three-phase motor, with the U, V, and W phase paths carrying power between the controller and motor. This code sets when the controller detects an open-circuit condition in the phase output, so the pump may not run as commanded.
Common causes
Most likely first.
- Open or damaged wiring to the pump
- Open pump motor winding
- Poor connector connection
Symptoms
- Check engine or transmission warning light on
- Harsh, delayed, or missing shifts
- Possible limp mode (locked in one gear)
- Slipping or shuddering during gear changes
How to diagnose it
- Capture freeze-frame data and check transmission live data for commanded auxiliary-pump operation and any pump or shift faults recorded at the same time.
- Inspect the pump's electrical connector and the U, V, and W phase wiring for disconnection, damaged insulation, corrosion, or loose terminals.
- Check continuity through each phase path between the pump and its controller using the vehicle wiring information.
- Test the pump motor windings for an open circuit using the manufacturer's procedure.
- If all phase wiring and motor windings are intact, check the pump controller output and its power and ground connections.
Common fixes
- Reconnect and secure a loose pump connector.
- Repair an open or damaged U, V, or W phase wire.
- Replace the auxiliary pump if a motor winding is open.
- Repair or replace the pump controller if its phase output is faulty.
Can I keep driving?
Avoid driving if the vehicle has delayed, harsh, slipping, or missing shifts, or has entered limp mode; the auxiliary pump may not maintain the operation the transmission needs. If shifting is normal, drive only as needed and get the fault diagnosed promptly.
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.