What it means
The control module detects phase W 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
The electric or auxiliary transmission-fluid pump’s three-phase motor circulates fluid to help maintain hydraulic pressure. The control module monitors phase W and sets P0B07 when current in that phase falls below the expected level, which can happen if the circuit is open or has high resistance.
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
- Save freeze-frame data and scan for related pump codes to establish when phase W current dropped and whether the fault is recurring.
- Check scan-tool pump data, if available, and compare phase W current with the other motor phases under the same operating conditions.
- With the vehicle made safe using its service information, inspect the phase W wire, pump connector, and terminals for breaks, corrosion, loose fit, or pulled-back pins.
- Test phase W wiring for an open or excessive resistance, including connector contacts, following the manufacturer’s procedure and specification.
- If the wiring path is sound, test the pump motor and current-sensing or control electronics to determine whether the motor is failing or the low reading is false.
Common fixes
- Repair an open or high-resistance section of phase W wiring.
- Clean, secure, or replace a poor pump connector terminal.
- Replace the pump motor if it fails the specified phase-current or winding tests.
- Repair the current-sensing or pump-control circuit if it incorrectly reports low phase W current.
Can I keep driving?
The transmission may restrict operation if phase W current is too low, so avoid demanding driving and do not rely on the vehicle for a long trip. Stop safely and arrange service if shifting is limited, slipping, or accompanied by a hybrid warning; inadequate fluid circulation can lead to transmission damage.
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.