P2C04: Fuel regulator D output stays high during an on command

P2C04 represents a short-to-power diagnosis on the low side of the fuel-quantity control-valve driver. The documented failure observation is high voltage while the driver is commanded on. That combination, rather than a voltage read without command context, is the useful starting point.

Why the output state matters

The neighbouring P2C03 monitor looks for low feedback with the driver off. P2C04 instead evaluates an on-state output that remains high. These complementary checks show why a meter reading taken in an unknown output state cannot establish the controller's complete diagnosis.

The source lists twenty events for qualification and a one-trip response, with battery, engine-speed and diagnostic-inhibit prerequisites. This is an event count; it should not be converted into an assumed twenty-second test or a specified number of driver pulses without the application routine.

Interpret electrical and pressure evidence together

Retain the short-to-power status and command state, then separately evaluate any rail-pressure deviation. Abnormal pressure can accompany a control-circuit problem, but does not identify which electrical branch failed. Conversely, pressure appearing normal at one moment does not establish recovery from an intermittent high-feedback event.

This summary does not provide a connector pinout, safe isolation sequence or replacement verdict. High-pressure fuel and powered driver testing require the exact service method. A valid repair check establishes that the on-state circuit monitor completed without reporting the high-side electrical condition; simply clearing the code or observing one pressure value is insufficient evidence.

Source and applicability

2025 GM 07A-2 documented monitor only; module and calibration applicability must be matched to the vehicle. The application-matrix filename join remains unresolved; no model or engine fitment is inferred. GM PDF, page 739.