P2798: Auxiliary transmission-pump control circuit is electrically low

P2798 diagnoses a ground-short signature in the auxiliary transmission-fluid pump motor circuit in the reviewed GM source. The low designation refers to electrical circuit behavior; it is not a direct finding of low transmission-fluid pressure.

What the controller detects

Circuit voltage is compared with a controller-specific accepted range. The ground-short design specification is less than 0.5 ohm between the signal and controller ground. The monitor uses thresholds above 20 failed counts and 25 sample counts, updated every 100 milliseconds.

A pump-pressure test and this electrical test answer different questions. Low hydraulic output does not prove this particular circuit fault, and a circuit-low code does not locate the failed wiring or motor element by itself.

Supply conditions define a valid observation

Battery voltage must be between 9 V and 15 V, and run/crank voltage must exceed 5 V for more than 25 milliseconds. Monitoring and reporting must both be enabled. The source allows either a mapped high-side-driver supply or a configuration without such a driver.

Identify the actual supply arrangement before interpreting an inactive driver or a low signal. The design impedance is not a safe instruction to resistance-test a live motor circuit.

Verification should show acceptable electrical response under the documented supply conditions and completion without recurrence. If pump pressure remains abnormal, that requires separate performance evidence. The source gives Type B, two-trip classification and does not authorize replacing the pump or transmission controller solely from P2798.

Source and applicability

Keep the stated transmission function and source calibration separate from other applications. GM diagnostic table, PDF page 1196.