P0B07: Auxiliary transmission-pump phase W current is insufficient

P0B07 identifies electric/auxiliary transmission fluid pump motor phase W current low. The 2018 GM HPC1 monitor looks for an open-circuit response by checking current near the W phase's expected electrical peak.

An active-drive test

The documented threshold is below 1 A, sustained for 0.4 seconds in a 0.6-second window. The controller needs Run drive state, normal PWM, inverter voltage above 50 V and a state other than active discharge. It also limits evaluation to a ±30-degree phase-axis window and requires squared current command above 14.97 A². Reporting is Type A, one trip.

These requirements explain why a low current during shutdown or another inactive state is not the same evidence. The monitor expects a response to a meaningful command at a particular electrical phase.

What a successful pump sound cannot prove

The DTC is phase-specific electrical evidence. Audible operation alone does not demonstrate that the W-phase current measurement meets the monitor's expectation, and the code does not directly report fluid delivery. Preserve the phase identity, current request and inverter state for the applicable procedure.

A qualified high-voltage technician should diagnose the sensing and power paths using the vehicle information. After repair, confirm the prescribed eligible current response rather than only clearing memory. This table does not provide motor-terminal test instructions or authorize running the pump through improvised external wiring.

Source and applicability

This explanation follows the documented GM monitor, not a verified application to every vehicle with this code. Confirm the vehicle, reporting module and calibration in current service information. GM diagnostic table, physical page 1381.