P2799Electric/Auxiliary Transmission Fluid Pump A Control Circuit High
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- P2799 is set when the control line of auxiliary pump A sits at too high a level, normally because it touches a powered wire. GM's 2025 TCM tables are the only public manufacturer description: the module measures under 0.5 Ω from the signal line to a voltage source in 20 of 25 samples spaced 100 ms apart, provided supply voltage is between 9 and 15 V, and treats the result as Type B with the MIL after two trips. The tables also show that the pump may be fed by one of several high-side drivers, and the check only runs while the relevant driver is on. CARB requires such actuator circuits to be monitored for shorts. Look for chafed harness sections near hot or moving parts and pins bridged by moisture. With the pump unusable, stop-start and pressure support at restart are lost.
- What you may notice
- MIL after two drive cycles
- Stop-start inoperative
- Rough engagement after an auto-start
- Likely causes
- LikelyControl wire shorted to a powered circuit
- PossibleMoisture bridging pins in the pump connector
- PossibleInternal short in the pump electronics
- RareFaulty high-side driver in the module
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Usually a job for a workshop.Typical cost: €50 – €900
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.