Pressure Control Solenoid "C" Control Circuit High
P0971 indicates the transmission control module detected a high voltage condition in the Solenoid C control circuit, typically the C pressure control solenoid. This solenoid regulates transmission fluid pressure and when it fails, the transmission may enter limp mode and exhibit harsh shifting or slipping.
What You Might Notice
- Check Engine Light illuminated
- Transmission shifts hard or bangs into gear
- Transmission slips when shifting
- Increased fuel consumption
- Transmission overheating
Most Common Causes
- 1
Shorted solenoid winding
The Solenoid C coil has developed an internal short, causing excessive current draw and high voltage readings at the PCM.
- 2
Wiring harness damage or corrosion
The solenoid control circuit wiring may have damaged insulation, loose connections, or corroded terminals causing resistance and high voltage spikes.
- 3
PCM or transmission control module fault
The transmission control module may have a faulty driver circuit or internal short that misreads or misdrives the solenoid circuit.
- 4
Solenoid connector pin damage
The connector pins on the solenoid or transmission harness may be corroded, loose, or improperly seated, causing intermittent high voltage signals.
How to Diagnose It
- 1
Check Shorted solenoid winding — The Solenoid C coil has developed an internal short, causing excessive current draw and high voltage readings at the PCM.
- 2
Check Wiring harness damage or corrosion — The solenoid control circuit wiring may have damaged insulation, loose connections, or corroded terminals causing resistance and high voltage spikes.
- 3
Check PCM or transmission control module fault — The transmission control module may have a faulty driver circuit or internal short that misreads or misdrives the solenoid circuit.
- 4
Check Solenoid connector pin damage — The connector pins on the solenoid or transmission harness may be corroded, loose, or improperly seated, causing intermittent high voltage signals.
How to Fix It
- 1
Inspect and repair wiring harness
Check the Solenoid C control circuit wiring for damaged insulation, corrosion, or loose connections. Repair or replace damaged sections and clean corroded terminals with electrical contact cleaner.
- 2
Replace Pressure Control Solenoid C
If wiring is intact, the solenoid itself is likely shorted internally and must be replaced. Drain transmission fluid, remove the old solenoid, install new one with fresh gasket, and refill fluid.
- 3
Check solenoid connector and pins
Disconnect the solenoid connector and inspect for corrosion, bent pins, or loose fit. Clean contacts with contact cleaner, reseat the connector firmly, and verify no debris is present.
- 4
Test and replace transmission control module
If all solenoid and wiring checks pass, the transmission control module may have a faulty driver circuit. Consult a transmission specialist or dealer to test and potentially replace the module.
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