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P0799 OBD-II Trouble Code: Pressure Control Solenoid “C” Intermittent

Check Engine Light

P0799 code definition

The P0799 trouble code detects an issue with one of the pressure control solenoids

What the P0799 code means

The P0799 code is a generic OBD-II trouble code that signals an error with an electronic pressure control solenoid, or possibly the entire solenoid circuit. While the P0799 code can signal an issue with the circuit or multiple solenoids, it specifically detects an error with the “C” solenoid. In vehicles with automatic transmissions, the Powertrain Control Module (PCM) uses data from the engine speed, vehicle speed, throttle position, and engine load to determine the proper hydraulic pressure in the transmission, which helps the transmission shift gears, and aids torque converter lockup. The PCM sends this data to the pressure control solenoids, which then regulate the hydraulic pressure. When the PCM detects that the determined ideal pressure level and the actual pressure level are not the same, then the P0799 code will be triggered.

What causes the P0799 code?

There are a few different things that can cause the P0799 trouble code:

  • Defective pressure control solenoid
  • Insufficient transmission fluid levels
  • Dirty transmission fluid
  • Damaged or faulty electrical components in the system, such as wires and connectors
  • Hydraulic blockages within the fluid passages in the internal transmission
  • Defective high pressure pump
  • Mechanical failures in the internal transmission
  • In rare cases, a defective PCM or transmission control module

What are the symptoms of the P0799 code?

The P0799 trouble code will often be accompanied by the Check Engine Light, which will illuminate on the instrument panel. The car will likely also have transmission problems, which can range from slippage and heating, to harsh shifting or even an inability to shift. It is possible that the torque converter clutch will also refuse to engage or disengage. The car will also likely experience diminished fuel efficiency.

How does a mechanic diagnose the P0799 code?

The P0799 code should be diagnosed with the help of a standard OBD-II trouble code scanner. A certified technician can use the scanner to view the freeze frame data and gather information about the code. The mechanic will also check to see if any additional trouble codes are present. If they are, the codes should be addressed in the order in which they appear on the scanner. The mechanic will then reset the trouble codes and restart the vehicle, to see if the code returns. If the code does not return after this reset, then it should be assumed that the code notes an intermittent issue, or that it was erroneously detected.

If the P0799 code does return, then the mechanic will begin by inspecting the transmission fluid. If the fluid is low it will be refilled, and if it’s dirty it will be replaced. However, if the fluid is heavily contaminated, then there are likely severe issues with the transmission, which may need to be rebuilt or replaced.

The technician will then perform a visual inspection of the electrical components. All damaged wires, connectors, and circuits will need to be replaced.

After this inspection, a manual pressure gauge can be used to check the hydraulic pressure in the system. This information should be compared to the manufacturer’s specifications to see if the pressure is accurate. If the pressure is low, it is likely an issue of blockage, or a malfunctioning pump, solenoid, or regulator. These components can then be inspected and replaced as needed.

If the issue is still not identified, the mechanic will have to perform a more thorough inspection of the entire internal transmission.

After any component is repaired or replaced, the mechanic will need to once again reset the trouble codes and restart the vehicle to see if the code returns. This helps the mechanic know as soon as the issue has been resolved.

Common mistakes when diagnosing the P0799 code

The most frequently made mistakes when diagnosing the P0799 trouble code come from a failure to properly follow the OBD-II diagnostic protocol. When addressing the P0799 code, the protocol should be followed step by step to guarantee an efficient and trustworthy inspection and repair.

It is fairly common for pumps to be replaced, when a simpler problem (such as damaged electrical components) was the only issue.

How serious in the P0799 code?

The drivability of a vehicle with the P0799 code can vary greatly. It is possible that the car is very drivable, with just a few performance issues. It is also possible that the car is virtually inoperable due to a failure to shift and a torque converter clutch that is not responding. For these reasons, and because continuing to drive the vehicle can cause severe damage to the transmission, the P0799 code should always be assessed and repaired as soon as possible.

What repairs can fix the P0799 code?

Repairs for the P0799 trouble code include:

Additional comments for consideration regarding the P0799 code

It is very common for the P0799 code to be accompanied by other codes that deal with similar issues, such as transmission slippage, torque converter clutch, gear ratio, and shift solenoid trouble codes.

This code only applies to vehicles that have automatic transmissions.

Need help with a P0799 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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