Powertrain, generic (extended)

P2799 Electric/Auxiliary Transmission Fluid Pump A Control Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

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.

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

Symptoms

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

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€50–900
Time0.5–3 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

aux trans pump awiring harness

Related codes

P2796P2798P2797P27A5

References: gsi.ext.gm.com, law.cornell.edu.