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P2779 OBD-II Trouble Code: Downshift Switch Circuit Range/Performance

check engine light

P2779 code definition

P2779 Trouble Code is for the downshift switch circuit range and performance, and it sets when the voltage or resistance signal is not within the specified range provided by the manufacturer.

What the P2779 code means

The code means there is an issue with the downshift switch. Only vehicles that have manually shifting automatic transmissions will have this code appear. In some instances, it will take multiple failure cycles before this code causes the malfunction light to come on in the vehicle.

What causes the P2779 code?

The following are some of the most common causes of the P2779 code:

  • Liquids being spilled on the upshift/downshift switch

  • Wiring and connector issues – damaged, corroded, shorted, or disconnected connectors or wiring

What are the symptoms of the P2779 code?

In many cases, the symptoms will be very limited, and many drivers may not notice any issues with their vehicles. They will find that the manual shifter function of the vehicle is not working, or that it places the transmission in limp-home mode. If this happens, it will be much easier to realize something is wrong with the vehicle. The vehicle will have a hard time shifting, for example.

How does a mechanic diagnose the P2779 code?

To diagnose the P2779 code, the mechanic will want to connect their OBD-II scanner to the vehicle’s onboard computer. This computer gathers data about the car, and it makes it possible to share that data with the scanner. Naturally, this will make diagnosing the problem with the vehicle much easier. The mechanic will also reset the vehicle and drive it. They do this to see whether the code returns or not. When the code returns, they know that it is something that is actually wrong with the vehicle and it was not triggered by mistake. They can then start their diagnosis on that particular issue.

Common mistakes when diagnosing the P2779 code

One of the biggest mistakes when diagnosing the P2779 code is forgetting that the most common reason for the problem is spilling liquid onto the upshift/downshift switch. Instead of addressing this issue, they believe that the transmission wiring has malfunctioned instead. It is important to look at the most likely cause when diagnosing and repairing vehicles.

How serious is the P2779 code?

It is always important to take your vehicle to a mechanic for regular tune-ups as well as when there is an issue with your vehicle. This is true even if your vehicle still seems to be running well. If you find that there are codes stored in the vehicle, you want to get them diagnosed and taken care of right away. While the P2779 code might not seem too serious, it has the potential to cause some issues with your ability to shift properly. That’s not something you want to deal with.

What repairs can fix the P2779 code?

The following are some of the repairs that mechanics might use when they repair the P2779 code:

  • Check the upshift/downshift switch for damage caused by liquids and repair or replace it.

  • Check the wiring for corrosion, shorts, and bad connections and repair as needed.

  • Replace the powertrain control module

Additional comments for consideration regarding the P2779 code

Keep in mind that it is very rare for the powertrain control module to be at fault in these cases. It is usually the result of spilling liquid on the upshift/downshift switch. If you have noticed any issues with your vehicle, or if you know that you have the code stored in your vehicle, don’t wait on getting it repaired. Even though it might not be causing you any issues when you are driving now, you don’t want to have the problem get worse. Take your vehicle to a mechanic as quickly as possible to get the repairs the vehicle needs.

Need help with a P2779 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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