OBD-II code P2799 indicates that the powertrain control module (PCM) or transmission control module (TCM) has detected a high voltage condition in the control circuit for the electric auxiliary transmission fluid pump. This pump is typically used in hybrid or start-stop vehicles to maintain hydraulic pressure when the engine is off, and a high circuit reading suggests a short to voltage, a failed pump, or wiring issues.
The pump motor or internal electronics may be shorted, causing excessive current draw or voltage feedback on the control circuit. This is the most common cause.
The control circuit wire may be chafed or pinched, contacting a power source and creating a constant high voltage reading.
Corrosion, bent pins, or a loose connector can cause high resistance or intermittent contact, leading to erratic voltage signals.
If the relay is stuck closed or internally shorted, it can supply continuous voltage to the control circuit, triggering the code.
An internal driver failure in the module is possible but rare. This should only be considered after all other causes are ruled out.
It is not recommended. The auxiliary pump may not function correctly, leading to transmission damage, loss of drive, or unsafe driving conditions, especially in hybrid vehicles that rely on the pump when the engine stops.
No, but it is the most common cause. Wiring issues, poor connections, or a faulty relay can also trigger this code. A thorough diagnosis is needed to avoid unnecessary parts replacement.
Almost never. Many drivers are mistakenly told to replace the control module, but the fault is usually in the pump, wiring, or relay. Module replacement should only be considered after all other possibilities are exhausted and confirmed by professional testing.
A technician will scan for codes, inspect the pump and wiring, test the control circuit for shorts, check the pump's resistance, and verify relay operation. Pinpoint tests from the vehicle's service manual are essential to avoid misdiagnosis.