GM Transmission Replacement: Entering the TUN Code, Running the Learn, and When Characterization Applies

What GM Programming Asks After a Transmission Replacement

After you replace a transmission on a Chevrolet, GMC, or Cadillac, the GM programming asks what was replaced: the transmission, the solenoid (valve) body, or a characterization refresh. Choose what you actually replaced. If you replaced the transmission, choose transmission.

Where to Find the TUN Code

When you choose transmission, the software asks for a 16-character code called the TUN. It is on a small placard on the passenger side of the transmission, low down, on the very bottom line. Type it exactly. A letter I and a number 1 are easy to mix up, and a wrong character is a common reason the programming fails.

If the Programming Loads and Then Fails

If the screen appears to load for several minutes and then fails, recheck the TUN code character by character. Then rescan the vehicle before repeating the procedure. In one case the configuration codes cleared and the vehicle ran even though the software showed an error. You still need to run the learn procedure.

Which Transmissions Use Characterization

The characterization and solenoid reset options usually apply only to 8-speed and 10-speed transmissions. A 6-speed, such as the 6L50, does not use them, so do not look for a characterization step on a 6-speed.

Used Transmission: Usually Just a Quick Learn

After installing a used transmission, a quick learn is usually all that is needed if the vehicle starts, runs, drives, and shifts smoothly. A flash is usually not required. Test drive the vehicle after the learn.

If the Vehicle Has Power or Shifting Problems

If there are power or shifting complaints after the replacement, the ECM and TCM may need programming, adaptations, and, on 8-speed and 10-speed units, solenoid characterization. Contact AETools at https://aetools.us or call (913) 856-6678 with the vehicle year and model, the transmission type, and the error shown.