P2799: Auxiliary transmission-pump control circuit detects unwanted power

P2799 is the auxiliary transmission-fluid pump motor short-to-power diagnosis in the reviewed GM strategy. Its circuit-high designation describes an electrical fault signature, not a measured hydraulic overpressure condition.

The voltage comparison identifies the fault class

The controller detects circuit voltage outside its permitted range. The design specification for a voltage short is less than 0.5 ohm between signal and controller voltage source. The monitor's counting thresholds exceed 20 failures and 25 samples, updated every 100 milliseconds.

These figures characterize detection, not a live-circuit resistance-testing procedure. The source does not identify a particular point where unwanted power enters the circuit or establish that the motor itself is defective.

Interpret the supply arrangement correctly

The enable window requires battery voltage above 9 V and below 15 V, plus run/crank voltage above 5 V for more than 25 milliseconds. Diagnostic monitoring and reporting must be enabled.

The table provides logic for pumps with a mapped high-side supply driver and for pumps without one. Confirm the actual architecture before treating a missing driver command as evidence of a fault. A supply-state observation must correspond to the configuration being evaluated.

Verification should demonstrate acceptable motor-control electrical behavior and completion without recurrence. A separate pressure or flow concern needs its own hydraulic evidence; P2799 cannot establish that conclusion from the high-circuit title alone. The source lists Type B, two-trip behavior, without prescribing pump, wiring-harness or controller replacement.

Source and applicability

Confirm the vehicle, transmission variant and relevant module before applying this monitor description. GM diagnostic table, PDF page 1197.