P0971 OBD-II Trouble Code: Pressure Control Solenoid C Control Circuit High

diagnostic check engine light

P0971 code definition

The P0971 trouble code detects an electrical issue with the pressure control solenoid C control circuit.

What the P0971 code means

The P0971 code is a standard OBD-II trouble code that identifies an error with the pressure control solenoid control circuit in valve C. The pressure control solenoid control circuit is an integral part of the automatic transmission. The powertrain control module (PCM) calculates the ideal hydraulic shift pressure (which is used to actuate shifting and torque converter lockup) based on the engine load, engine speed, vehicle speed, and throttle position. The pressure control solenoids are then in charge of regulating the hydraulic pressure, as controlled by the PCM. When the PCM receives an abnormally high voltage reading from the pressure control solenoid control circuit in valve C, then the P0971 code will be stored.

What causes the P0971 code?

Many things can cause the P0971 code to be detected, such as:

  • Faulty valve C pressure control solenoid
  • Low transmission fluid level
  • Dirty or contaminated transmission fluid
  • Defective high pressure pump
  • Damaged electrical components, such as wires, connectors, and fuses
  • Hydraulic blockages in the internal transmission hydraulic system
  • Mechanical problems in the internal transmission
  • In very rare cases, a defective PCM or transmission control module (TCM)

What are the symptoms of the P0971 code?

The P0971 trouble code will usually be accompanied by an illuminated check engine soon Warning Light, as well as diminished fuel efficiency. It is likely that the vehicle will experience transmission problems, which may include extremely harsh shifting, slippage, overheating, constant stalling, and possibly a complete inability to shift gears.

How does a mechanic diagnose the P0971 code?

The P0971 code should be diagnosed using an OBD-II trouble code scanner. A trained technician will view the freeze frame data from the scanner to analyze the code, and to check for the existence of additional trouble codes. If numerous codes are detected, then they will need to be inspected in the order in which they are displayed on the scanner. The mechanic will then reset the trouble codes and restart the vehicle, and check to see if the code remains detected. If the mechanic notes that the code is no longer present, then an intermittent error or an inaccurate trigger are to blame.

If the P0971 code remains detected, then the technician should check the transmission fluid. If the fluid level is insufficient, then it should be refilled, and the mechanic should thoroughly check to see if there is a leak somewhere. If the fluid is dirty, it will need to be flushed out and replaced. If the fluid is contaminated, then there is probably a severe mechanical issue with the transmission, and a complete rebuild or replacement is likely in order.

The technician will then visually inspect the electrical components, replacing all shorted wires, damaged connectors, or blown fuses. Next, a manual pressure gauge will be attached to the hydraulic pump system, so a mechanic can compare the hydraulic pressure to the manufacturer’s specifications. If the pressure is abnormally low, then there is either a hydraulic blockage, or a defective solenoid, pump, or pressure regulator.

If the issue is not yet found, then a comprehensive inspection of the transmission, PCM, and TCM will be necessary.

When the mechanic replaces any component, the inspection should be paused while the trouble codes are once again reset, and the vehicle restarted. The technician can then check for the presence of the P0971 code. This allows the mechanic to know as soon as the problem has been resolved.

Common mistakes when diagnosing the P0971 code

The most frequently made mistake when diagnosing the P0971 code is the failure to comply with the OBD-II diagnosis protocol. It is imperative that mechanics always abide by the protocol completely, to help guarantee inspections and repairs that are accurate and efficient.

Often high pressure pumps are replaced erroneously, when an electrical issue was the only error.

How serious is the P0971 code?

A vehicle with the P0971 code will likely be drivable, though it may stall with regularity. It is also possible that an inability to shift will keep the car from being drivable at all. Even if the car is driving with few detectable symptoms, severe damage can be done to the transmission. For this reason, it’s important to schedule an inspection as soon as the P0971 code is detected.

What repairs can fix the P0971 code?

The repairs for the P0971 trouble code are:

Additional comments for consideration regarding the P0971 code

The P0971 trouble code will only be found in cars that have automatic transmissions.

Need help with a P0971 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

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