Pressure Control Solenoid C Electrical
The P0798 code indicates that the Powertrain Control Module (PCM) or Transmission Control Module (TCM) has detected an electrical malfunction in the circuit for transmission pressure control solenoid 'C'. This code is set when the module observes voltage or resistance values from the solenoid circuit that fall outside of the manufacturer's expected parameters.
This code is considered high severity because driving with improper transmission line pressure can cause severe internal transmission damage. It is highly recommended to stop driving and diagnose the issue immediately to prevent costly repairs.
Common symptoms
- Illuminated Check Engine Light
- Transmission slipping between gears
- Harsh, delayed, or erratic shifting
- Vehicle entering a fail-safe or 'limp' mode
- Decreased fuel efficiency
Likely causes
- Faulty transmission pressure control solenoid 'C'
- Damaged, corroded, or loose wiring and connectors in the solenoid circuit
- Low, dirty, or contaminated transmission fluid
- Clogged internal transmission fluid passages or filter
- Faulty Transmission Control Module (TCM) or PCM
What to check before replacing parts
Check the transmission fluid level and condition.
Look for: Fluid that is low, burnt, or heavily contaminated with debris, which can cause pressure issues or indicate internal transmission wear.
Visually inspect the wiring harness and connectors associated with pressure control solenoid 'C'.
Look for: Frayed wires, melted insulation, or corroded connector pins that could cause an open or short circuit.
Test the resistance of pressure control solenoid 'C' using a digital multimeter.
Look for: Resistance readings that fall outside the manufacturer's specified range, indicating a failed internal solenoid coil.
Check for proper voltage and ground signals at the solenoid connector while the key is on.
Look for: A lack of battery voltage or a poor ground signal from the TCM, which points to a wiring issue between the module and the solenoid.
Monitor live transmission data with an advanced scan tool while driving.
Look for: Discrepancies between the TCM's commanded solenoid duty cycle and the actual transmission line pressure behavior.
This page explains the generic P0798 definition and is general reference information, not a diagnosis for your specific vehicle. Actual causes, severity, and repairs vary by make, model, engine, and mileage — always confirm with a scan tool and a qualified technician before replacing parts.
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