This article is about failure, something we all experience from time to time. If you are attempting to perform a fast learn process on a GM eight-, nine-, or 10-speed transmission, you may have that temporary feeling of failure, as this process can bring on frustration quickly. Let’s talk about what the fast learn process is, and what you need to know.
What is a fast learn process?
Fast learn is a stationary process in the bay that will require your scanner or J2534 pass-through interface to initiate the process. It allows the Transmission Control Module (TCM) to learn clutch apply pressures and characteristics that may be used in the adaptive relearn procedure after a repair.
The fast learn procedure will speed up the adaptive process, but be aware that some measures (such as TCC adapts/relearn after the process is performed) may still take 200 to 300 miles of driving. In most cases though, if the TCM is updated to the latest program, the unit is secure hydraulically, the valve body is functional and solenoids are performing properly, then that transmission will be ready to deliver in short order.
Here’s one programming tip when using a J2534 pass-through device to program TUN or PUN: if you are installing a new or remanufactured 8L unit from GM, it no longer comes with a piece of paper containing the TUN and PUN info. To program a replacement unit, you only need the TUN information that is plainly visible on the outside of the case. The only time you would need PUN during programming is when replacing the valve body with a GM-provided valve body.
Fast learn basic requirements and when/how it should be initiated
Fast learn should be initiated after any type of transmission repair. This includes a transmission flush with new ATF, provided the flush is to correct TCC shudder or slip.
The temperature must be at 167°F (75°C) and 185°F (85°C), but it also depends on current TCM programming. If your vehicle TCM program has a temperature requirement different than this, it may need an update to its programming.
Use VIN found online at ACDelco Technical Delivery System (TDS) Service Programming System (SDS2) to verify the latest programming.
Note: The temperature requirement is also the hardest part of the fast learn procedure. If you have installed a thermal bypass device, it may take two hours or more in the bay power braking to reach the required temperature. A better method is to install a thermal bypass after fast learn and adaptations are complete. You may even want to bypass the cooler through artificial means to temporarily bring temperature up and initiate fast learn.
Transmission line pressure must be normal at 55 to 60 PSI minimum, with pressure rise on throttle in Drive, and ATF level must be correct and verified.
Follow the procedures on scanner exactly, and be sure to pay attention. A tip: Use the data-logging features of the HP Tuner’s scanner application. Then, if it fails, you know exactly what caused the failure.
What can prevent fast learn from completing?
- Clutch circuit leaks of any kind, including sealing rings, piston wear or cracks, piston seals and clutch clearance.
- Unit assembly mistakes.
- Valve body issues, such as:
- Wear in the solenoid signal accumulators or clutch regulator valves and bores.
- Pressure regulator and shuttle valve wear causing line pressure issues.
- Solenoid failure or functionality issues.
- Worn accumulator and valve body end plugs.
- Valve body assembly mistakes such as loose bolts, checkballs left out or in the wrong location.
- Cut o-rings on a solenoid (see Figure 1).
- System voltage issues such as a battery failing, faulty alternator output and power or ground issues, especially involving the external TCM on an 8L unit.
- Powertrain codes (P codes) in the vehicle including ABS, engine and transmission.
- Engine issues such as misfires, fuel or air issues.
- Low fuel: The vehicle must have between one-fourth and three-fourths of a tank of fuel for fast learn and the subsequent driving cycle relearn process.
If your scanner will not initiate fast learn first, try another scanner. Also, try shutting the driver’s side door. I’m unsure why, but on one vehicle after repeated attempts to initiate fast learn, shutting the driver’s side door allowed fast learn to initiate immediately. (Who knows!) Make certain the TCM has the latest programming; some 2015 8L models will not perform a fast learn until updated.
If by chance fast learn does not complete, be grateful if you receive a scanner message stating the problem area (see Figure 2). That message does not always appear.
A huge thank you to the many shops and technicians that helped this material evolve!
Jim Mobley is a Sonnax technical communication specialist. He is a member of the Sonnax TASC Force (Technical Automotive Specialties Committee), a group of recognized industry technical specialists, transmission rebuilders and Sonnax technicians.
