P0798 Fault Code in Ford: Causes, Symptoms, and Fixes

The TCM (Transmission Control Module) detects an electrical fault in the circuit controlling Pressure Control Solenoid C. Unlike P0797 (stuck on), this one points specifically to electrical issues rather than mechanical sticking.

Symptoms:

1. Harsh / delayed shifts
2. Transmission stuck in fail-safe or limp mode
3. Slipping under load
4. Possible overheating of transmission
5. Check Engine Light (CEL) or transmission warning lamp

Common Causes:

1. Faulty pressure control solenoid C (internal electrical failure)
2. Open or short circuit in solenoid wiring harness
3. Corroded or loose connectors at solenoid or TCM
4. Low / dirty transmission fluid (can worsen solenoid behavior)
5. Faulty TCM/ECM (less common)

Diagnostic & Fix:

1. Check transmission fluid – level & condition. Replace if burnt/dirty.
2. Inspect wiring harness & connectors – look for broken, frayed, or corroded wires.
3. Measure solenoid resistance with a multimeter → compare with manufacturer spec.
4. Check continuity in the circuit between TCM and solenoid.
5. If wiring is fine → Replace solenoid C.
6. If problem persists → possible TCM fault or internal hydraulic issue.