P2799: Auxiliary Transmission Fluid Pump Control Circuit High
The P2799 code indicates that the Powertrain Control Module (PCM) has detected a high voltage condition in the control circuit of the auxiliary transmission fluid pump. This pump is typically used in start-stop systems to maintain transmission fluid pressure when the engine is off. A high voltage reading suggests a short to power, a faulty pump, or a wiring issue. This can lead to improper pump operation, potentially causing transmission damage or drivability issues.
1. Most Common Causes
- Short circuit to battery voltage (B+) in the auxiliary pump control circuit wiring
- Auxiliary pump control relay stuck closed or damaged
- Internal short circuit failure in the transmission fluid auxiliary pump module
- Corroded, loose, or damaged harness connectors or terminals
- Excessive resistance in the auxiliary pump ground circuit
- PCM failure (less common, but possible)
2. Symptoms You Will Notice
- Check Engine Light illuminated
- Transmission slipping or harsh shifting
- Start-stop system malfunction
- Transmission overheating
3. Step-by-Step Diagnosis
Step 1: Use a scan tool to retrieve all codes and freeze frame data.
Step 2: Inspect the auxiliary pump wiring and connectors for damage, corrosion, or shorts.
Step 3: Test the pump control circuit voltage with a multimeter; compare to manufacturer specs.
Step 4: Check the pump resistance and operation; replace if faulty.
Step 5: Clear codes and test drive to verify repair.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended. Driving with P2799 can cause transmission damage due to inadequate fluid pressure, especially in stop-start conditions.
How much does it cost to fix?▼
Repair costs typically range from $200 to $600, including parts and labor. The auxiliary pump itself costs $100-$300, plus diagnostic time.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.