Pressure Control Solenoid C Intermittent
The Powertrain Control Module (PCM) or Transmission Control Module (TCM) detected an intermittent electrical malfunction or erratic voltage in the transmission pressure control solenoid 'C' control circuit. This solenoid regulates hydraulic pressure to ensure smooth gear shifts, and an intermittent signal indicates an unstable connection or a failing component.
This code requires prompt attention because erratic hydraulic pressure can cause severe internal transmission damage or trigger limp mode. Continued driving may lead to costly repairs or a breakdown.
Common symptoms
- Illuminated Check Engine Light
- Harsh, erratic, or delayed transmission shifts
- Transmission slipping between gears
- Vehicle stuck in limp mode (restricted to a single gear)
- Decreased fuel economy
Likely causes
- Low or contaminated transmission fluid
- Loose, corroded, or damaged wiring and connectors in the solenoid circuit
- Faulty transmission pressure control solenoid 'C'
- Clogged transmission fluid filter or internal hydraulic passages
- Failing transmission pump
- 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 metal shavings, which indicates hydraulic issues or internal wear.
Inspect the wiring harness and connectors for solenoid C.
Look for: Loose pins, corrosion, melted wires, or signs of intermittent contact that could cause erratic electrical signals.
Test the resistance of pressure control solenoid C using a multimeter.
Look for: Resistance values that fall outside the manufacturer's specified range, or readings that fluctuate when the solenoid is tapped lightly.
Check the solenoid control circuit for continuity and shorts to ground.
Look for: High resistance, an open circuit, or a short to ground between the TCM and the solenoid connector.
Perform a transmission hydraulic pressure test.
Look for: Erratic or out-of-spec line pressure readings that confirm the solenoid is failing to regulate pressure mechanically.
This page explains the generic P0799 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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