P2799: Electric/Auxiliary Transmission Fluid Pump A Control Circuit High

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.

Medium severity. Can I keep driving?Drive gently to a repair shop. If it slips, you hear clunks, or it loses its gears, do not keep driving.

Symptoms

MIL after two drive cycles
Stop-start inoperative
Rough engagement after an auto-start

Most likely causes

Control wire shorted to a powered circuit
Moisture bridging pins in the pump connector
Internal short in the pump electronics
Faulty high-side driver in the module

What to check, in order

Start with the simplest. You can tick off each step.

Check the fluid level and condition
Check the sensor's ground and make sure the signal wire is not receiving voltage from another circuit.
Read the input and output speed in live data
Check the connector and wiring
Check for other related engine codes
Consult the manufacturer's procedure for the transmission

Good to know

Repair difficulty: medium
It can trigger limp mode.
It affects emissions.

What each character of P2799 means

P: Powertrain: engine and transmission
2: Generic code: same on every make
7: Transmission
99: Specific fault in that system

Frequently asked questions

Can I keep driving with code P2799?

Drive gently to a repair shop. If it slips, you hear clunks, or it loses its gears, do not keep driving.

What causes code P2799?

The most common causes are: control wire shorted to a powered circuit; moisture bridging pins in the pump connector; internal short in the pump electronics.

Related codes

Sources

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.