A pressure control solenoid is an electromechanical device that the ECU uses to set the hydraulic pressure for each shift. If it detects an unusually high-voltage signal on the pressure control solenoid C circuit, it will save a P0971 DTC.
How Serious is the Code?
The P0971 diagnostic trouble code is quite serious, because the ECU is not in total control of the hydraulic pressure inside the transmission. This will cause a number of transmission problems that include slipping, unusually harsh gear changes and engine stalling.
Symptoms of a P0971 include:
- Transmission slips in and out of gear
- Hard gear changes
- Transmission overheats
- Engine will stall
- Engine misfire-like symptoms
- Limp mode
- Transmission fluid and filter have become contaminated
- Wiring has been damaged
- Connectors are either broken or corroded
- Broken pressure control solenoid
- Broken transmission pump
- Valve body failure
- TCM/ECU problems
How to Diagnose the Code?
The first step to diagnosing a P0971 OBDII trouble code, is to check the level and condition of the transmission fluid. If it looks clean and there are no metal fragments or a burnt smell, then the wiring and connectors along the transmission wiring harness will need to be checked for signs of damage and corrosion. If no shorted wires or broken connectors are found, then the pressure control solenoid(s) will need to be checked, along with possibly the transmission pump and valve body.
What Repairs Will Fix P0971?
- Change the transmission fluid and filter
- Repair or replace damaged wiring and connectors
- Install new pressure control solenoid(s)
- Repair or replace transmission pump
- Repair or replace the valve body
- Reprogram or replace the ECU or TCM
- P0968 – Pressure Control Solenoid “C” Control Circuit/Open
- P0969 – Pressure Control Solenoid “C” Control Circuit Range/Performance
- P0970 – Pressure Control Solenoid “C” Control Circuit Low