P0798 - Pressure Control Solenoid C Electrical Malfunction
The P0798 code indicates an electrical fault in the pressure control solenoid 'C' circuit, which is part of the transmission's hydraulic control system. This solenoid regulates line pressure for shifting. The Powertrain Control Module (PCM) detects an abnormal voltage or resistance in the solenoid circuit, often due to wiring issues, connector problems, or a faulty solenoid. This can lead to harsh or erratic shifting, slipping, or limp mode.
1. Symptoms You Will Notice
- Check Engine Light illuminated
- Harsh or delayed shifts
- Transmission slipping
- Vehicle stuck in limp mode (e.g., 2nd gear only)
- Poor fuel economy
2. Most Common Causes
- Faulty transmission pressure control solenoid 'C' with damaged coil
- Short to ground in wiring or connector between TCM and solenoid 'C'
- Short to battery voltage in wiring or connector between TCM and solenoid 'C'
- Open circuit in solenoid 'C' harness due to break, corrosion, or disconnection
- Excessive resistance in connector or terminals due to oxidation or contamination
- Internal TCM failure in the solenoid driver circuit
- Transmission connector contaminated with moisture, oil, or mechanically damaged
3. Step-by-Step Diagnosis
Step 1: Scan for codes and record freeze frame data.
Step 2: Inspect transmission fluid level and condition; top off or replace if necessary.
Step 3: Visually check wiring and connectors for damage, corrosion, or loose pins.
Step 4: Test solenoid resistance with a multimeter (typically 4-6 ohms); compare to specs.
Step 5: Check for power and ground at solenoid connector with key on; repair as needed.
Step 6: If all else passes, replace pressure control solenoid C.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended. Driving with P0798 can cause transmission damage due to harsh shifting or slipping. You may be limited to limp mode, which reduces speed and drivability.
How much does it cost to fix?▼
Costs range from $200 to $600 depending on labor rates and parts. DIY solenoid replacement is cheaper (part ~$50-$150), but professional diagnosis and repair may be needed for wiring issues.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.