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P0798 — Pressure Control Solenoid C Electrical

Generic OBD-II · all makesPowertrain (engine & transmission)

P0798 indicates that the transmission control system has detected an electrical fault in the circuit for pressure control solenoid C. This solenoid regulates transmission line pressure for specific clutch applications, and an electrical fault means the control module cannot properly command or monitor it.

Symptoms

What causes it — most likely first

1. Pressure control solenoid C internal failure

The solenoid coil itself has failed open, shorted, or has excessive resistance. This is the most common cause of an electrical code for this specific solenoid.

2. Wiring harness damage

Chafed, broken, or corroded wiring between the solenoid and the control module can create an open or short circuit. Heat and vibration near the transmission make this a frequent failure point.

3. Connector corrosion or loose pins

Corroded, bent, or pushed-back terminals at the solenoid connector or the transmission pass-through connector can interrupt the circuit without damaging the solenoid itself.

4. Transmission fluid contamination

Severely degraded or contaminated fluid can cause solenoid sticking or internal shorting, though this typically produces performance codes alongside or before a pure electrical fault.

5. PCM/TCM driver circuit failure

The control module's internal driver transistor for solenoid C has failed. This is uncommon and should only be considered after the solenoid and all wiring have been verified good.

How it's diagnosed

  1. Scan all modules for additional transmission codes and record freeze frame data to understand operating conditions when the code set.
  2. Consult the vehicle-specific wiring diagram to identify the exact pins and wire colors for pressure control solenoid C at both the solenoid and the control module.
  3. Perform a visual inspection of the transmission harness, pass-through connector, and solenoid connector for corrosion, bent pins, or chafed insulation.
  4. With the key off, measure resistance across the solenoid C terminals and compare to specification; an out-of-range or infinite reading indicates an internal solenoid failure.
  5. If solenoid resistance is within spec, perform a wiggle test and voltage drop test on the wiring between the solenoid and the control module to locate intermittent opens or shorts.
  6. Only after the solenoid and entire circuit are confirmed good, scope the command signal at the control module connector to verify the driver is functioning; a missing or corrupted signal at that point supports a module fault.

Code facts & related codes

SystemPowertrain (engine & transmission)
StandardizationSAE generic — identical on every make
Related codesP0790 — Normalperformance Switch CircuitP0791 — Intermediate Shaft Speed Sensor CircuiP0792 — Intermediate Shaft Speed Sensor CircuiP0793 — Intermediate Shaft Speed Sensor CircuiP0794 — Intermediate Shaft Speed Sensor CircuiP0795 — Pressure Control Solenoid C

Frequently asked

Can I drive with code P0798?

Short distances may be possible, but continued driving risks harsh shifts and internal transmission damage. The transmission may also enter limp mode, leaving you with limited gears. Have it diagnosed promptly.

Does P0798 mean I need a new transmission?

No. The code points to an electrical circuit fault involving one solenoid and its wiring. Most repairs involve replacing a solenoid or repairing a connector, not rebuilding or replacing the transmission.

Should I replace the PCM or TCM for P0798?

Almost never. Shops and forums sometimes jump to the control module, but the solenoid and wiring are far more likely culprits. A PCM/TCM driver failure is rare and should only be suspected after the solenoid, connector, and harness have all been electrically verified as good.

Is it safe to just replace the solenoid without testing?

It is a reasonable first step given how common solenoid failures are, but skipping wiring and connector checks risks a misdiagnosis. A corroded connector or chafed wire will set the same code even with a new solenoid installed.