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DTC codes / P09xx · Transmission / P0971

P0971Pressure Control Solenoid 'C' Control Circuit High

P0971 indicates that the transmission control module (TCM) has detected an abnormally high voltage on the control circuit for pressure control solenoid 'C', which is used to regulate hydraulic pressure inside the automatic transmission. The circuit is typically commanded by the TCM to ground, so a high voltage reading means the circuit is open, shorted to power, or the solenoid's internal coil has failed.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyProfessional
AreaTransmission

Symptoms you may notice

  • Illumination of the check engine light or transmission warning light, often with no other noticeable symptoms
  • Harsh or delayed gear shifts, especially when the transmission is cold
  • The transmission may enter limp mode, stuck in a single gear or neutral
  • Slipping or flaring during gear changes under acceleration
  • Poor fuel economy or unusual engine RPM behavior at steady speeds

Common causes, most likely first

  1. Open or damaged wiring in the pressure control solenoid 'C' control circuit, such as a broken wire or corroded connector
  2. Short to voltage on the control circuit, often from chafed insulation or a pinched harness
  3. Faulty pressure control solenoid 'C' with an open internal coil or high resistance
  4. Poor electrical connection at the solenoid or TCM connector, including loose pins or water intrusion
  5. Failed transmission control module (TCM) driver circuit, though this is less common
  6. Internal transmission mechanical issues that cause the solenoid to overheat and fail

How to diagnose and fix it

  1. Use a scan tool to verify the code and check for any related transmission codes or freeze-frame data
  2. Inspect the wiring harness and connectors at the transmission and TCM for damage, corrosion, or loose pins
  3. Measure the resistance of pressure control solenoid 'C' with a multimeter and compare to the manufacturer's specification
  4. Check for short to voltage or open circuit by backprobing the control circuit at the TCM while commanding the solenoid on and off
  5. If the circuit tests good, replace the pressure control solenoid 'C' and clear the codes
  6. If the solenoid and wiring are good, test the TCM driver circuit and replace the TCM if faulty
  7. After repairs, perform a transmission adaptive relearn procedure and verify the code does not return

Don't overlook the wiring harness first

  • A common misdiagnosis is replacing the solenoid when the real problem is a chafed wire in the harness near the transmission mount or a corroded connector pin.
  • P0971 can be set by a low battery or charging system issue that causes the TCM to see erratic voltage, so always check battery and ground connections before condemning parts.
  • Some vehicles use a single solenoid for multiple pressure control functions, so a failure in a related circuit can trigger P0971 even if solenoid 'C' itself is fine.
  • The code may appear intermittently due to temperature-related expansion of a failing solenoid coil, so a cold resistance test can miss a hot failure.
  • After replacing a solenoid, the TCM often needs a relearn or adaptation reset; skipping this step can cause harsh shifts that mimic a recurring fault.

Can I keep driving with P0971?

You can usually drive the vehicle to a repair shop if the transmission is not in limp mode, but avoid aggressive acceleration or heavy towing because pressure control faults can cause harsh shifts and internal damage. If the transmission slips severely or refuses to shift, stop driving and have it towed.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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