P0787 3-4 Shift Malfunction

How to Fix P0787 3-4 Shift Malfunction


If you’re experiencing a P0787 error code on your vehicle, it means that there is a malfunction in the 3-4 shift circuit. This can cause your vehicle to shift poorly or not at all, which can be frustrating and dangerous. However, with a little bit of knowledge and some basic tools, you can fix this issue yourself and save money on costly repairs.

Step 1: Check the Wiring

The first step in fixing a P0787 error code is to check the wiring. This is often the cause of the issue, as the wiring can become damaged or corroded over time. Start by inspecting the wiring harness for any visible damage or corrosion. If you see any issues, you’ll need to replace the damaged wiring.

Step 2: Check the Solenoid

If the wiring looks good, the next step is to check the solenoid. The solenoid is responsible for controlling the flow of fluid in the transmission, which allows it to shift gears. To check the solenoid, you’ll need to remove the transmission pan and locate the solenoid. Check for any visible damage or wear, and replace the solenoid if necessary.

Step 3: Check the Transmission Fluid

Another common cause of a P0787 error code is low or dirty transmission fluid. If the fluid is low, it can cause the transmission to shift poorly or not at all. Check the fluid level and condition, and replace it if necessary. Be sure to use the correct type of fluid for your vehicle, as using the wrong type can cause further damage.

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Step 4: Check the Transmission Control Module

If the wiring, solenoid, and fluid all look good, the issue may be with the transmission control module (TCM). The TCM is responsible for controlling the transmission, and a malfunctioning TCM can cause a variety of issues, including a P0787 error code. To check the TCM, you’ll need to use a diagnostic tool to read the error codes and check for any other issues.

Step 5: Replace the Transmission

If none of the above steps fix the issue, it may be time to replace the transmission. This is a more costly and time-consuming repair, but it may be necessary if the transmission is severely damaged or worn out. Be sure to have a professional mechanic perform this repair, as it requires specialized knowledge and tools.


Fixing a P0787 error code can be a frustrating and time-consuming process, but with the right knowledge and tools, it can be done. Start by checking the wiring, solenoid, and fluid, and if those don’t work, move on to checking the TCM or replacing the transmission. With a little bit of patience and perseverance, you can get your vehicle back on the road in no time.


1. Can I drive my vehicle with a P0787 error code?

It’s not recommended to drive your vehicle with a P0787 error code, as it can cause your vehicle to shift poorly or not at all. This can be dangerous and can cause further damage to your transmission.

2. How much does it cost to fix a P0787 error code?

The cost of fixing a P0787 error code can vary depending on the cause of the issue. Simple repairs like replacing the wiring or solenoid can cost a few hundred dollars, while more complex repairs like replacing the transmission can cost several thousand dollars.

3. How can I prevent a P0787 error code from happening?

To prevent a P0787 error code from happening, it’s important to maintain your vehicle’s transmission and fluid. Regularly check the fluid level and condition, and have your transmission serviced according to the manufacturer’s recommendations. Additionally, avoid driving your vehicle in extreme conditions, as this can cause damage to the transmission.