Auxiliary Transmission Fluid Pump Control Circuit Low
The P2798 code indicates that the powertrain control module (PCM) has detected a low 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 low circuit voltage can be caused by a faulty pump, damaged wiring, poor electrical connections, or a failed control module. This issue can lead to delayed engagement, transmission slipping, or overheating.
1. Most Common Causes
- Open or short-to-ground in the auxiliary pump signal or power circuit
- Faulty auxiliary transmission fluid pump (internal motor shorted or open)
- Blown or stuck auxiliary pump control relay
- Corroded, loose, or damaged connector terminals in the pump circuit
- Internal output driver failure in the TCM/PCM
2. Symptoms You Will Notice
- Check Engine Light illuminated
- Transmission slipping or delayed engagement
- Transmission overheating
- Start-stop system malfunction
3. Step-by-Step Diagnosis
Step 1: Use a scan tool to retrieve all stored codes and freeze frame data.
Step 2: Inspect the auxiliary transmission fluid pump and its wiring for damage, corrosion, or loose connections.
Step 3: Test the pump circuit voltage and ground with a multimeter; compare to manufacturer specifications.
Step 4: Check the fuse and relay for the auxiliary pump; replace if blown.
Step 5: If all else is okay, test the pump itself by applying direct power and ground; replace if it doesn't operate.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive with this code, as it can cause transmission damage due to insufficient lubrication and cooling, especially in stop-and-go traffic.
How much does it cost to fix?▼
The cost to fix P2798 typically ranges from $150 to $400, depending on whether the pump needs replacement or just wiring repairs.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.