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P0797 OBD-II Trouble Code: Pressure Control Solenoid C Stuck On

Check Engine Light

P0797 code definition

A P0797 trouble code indicates that the Powertrain Control Module (PCM) has detected a problem in one of the electronic pressure control solenoids or solenoid circuits. Found in automatic transmissions, electronic pressure control solenoids receive their instructions from the PCM.

When diagnosing a P0797 trouble code, the mechanic should also look for codes P0795, P0796, P0798, and P0799.

What the P0797 code means

Using calculations based on the load on the engine, engine speed, vehicle speed, and throttle position, the PCM determines how much pressure the hydraulic pump should apply to the transmission. When there is a discrepancy between the amount of pressure applied and the amount desired, a P0797 trouble code is stored.

What causes the P0797 code?

Some common causes of a P0797 trouble code include:

  • A bad electronic pressure control solenoid
  • Low and/or dirty transmission fluid
  • Transmission failure
  • A faulty PCM or TCM
  • A faulty hydraulic pump or hydraulic line blockage within the transmission

What are the symptoms of the P0797 code?

Symptoms of a P0797 trouble code include disabled shift functioning, failure of the torque converter to engage, harsh shifting, and transmission slippage and overheating. In addition, the vehicle could experience a decrease in fuel efficiency.

How does a mechanic diagnose the P0797 code?

To diagnose a P0797 trouble code, the mechanic needs a code reader, manual pressure gauge, hydraulic pressure diagram, and a digital volt/ohmmeter. The mechanic also needs to perform the following steps:

  • Start by pulling the transmission dipstick to check fluid level and condition

  • When examining the transmission fluid, look for abnormal looking or burnt smelling fluid

  • If the fluid looks strange or smells burnt, drop the transmission pan and look for evidence of debris. This signifies a damaged transmission, requiring the mechanic to rebuild it

  • The mechanic should also fill the transmission fluid to a level to allow them to detect any leaks

  • Once any leaks have been found and repaired and the transmission rebuilt if damaged, the mechanic should fill the transmission fluid to a normal level and start the vehicle, allowing the engine to reach a normal operating temperature

  • Clear the P0797 trouble code and test drive the vehicle to see if the code persists

  • Examine the wiring, connectors, and components for fault or damage. This usually requires the replacement of the entire internal transmission harness by the mechanic

  • If after clearing the trouble code it returns, connect the scanner to the diagnosis connector and download any stored codes and freeze frame data

  • Using a hydraulic pressure diagram, hook a manual pressure pump to the transmission and check the pressure produced by the hydraulic pump against the manufacturer's specifications

  • If the code returns, use the digital volt/ohmmeter to check the reference voltage and ground signal of the electronic pressure control solenoid that is producing the trouble code

  • If the reference voltage or ground signal is open, check the continuity and resistance of all related circuits. The mechanic should make sure to disconnect any control module son the circuit to avoid damage and memory loss

  • If everything checks out and the code returns after clearing, test the PCM for fault

  • Clear the P0797 trouble code and test the system to see if it returns

Common mistakes when diagnosing the P0797 code

A common mistake is for a mechanic to replace the high pressure pump when the problem actually lies with the electronic pressure control solenoid or faulty wiring. In cases such as this, the problem is not repaired and the trouble code returns.

How serious is the P0797 code?

The causes of a P0797 trouble code can lead to problems with shifting, malfunction of the transmission and torque converter, and a reduction in overall fuel efficiency.

What repairs can fix the P0797 code?

To repair a P0797 trouble code, the mechanic needs to take the following steps:

Need help with a P0797 code?

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