Shifty Business

Back in the early 1980's we saw electronically controlled transmissions hit the market on foreign and domestic vehicles. Early on, electronics may have controlled one or more shift solenoids and the lockup converter function, but not much else.

Fast forward to today and everything is electronic control. In most vehicles, there is little, to no mechanical connection between you and the vehicle including gear selection. Your vehicle's computer takes your inputs and determines the appropriate application of the outputs it controls. Shift Tables and Adaptive Learning are two different concepts related to automotive transmission operation and performance. Let's define each separately:

Transmission shift tables

In an automatic transmission, the shift table refers to a pre-programmed set of parameters and instructions that dictate when and how the transmission should shift gears. It is essentially a lookup table that determines the appropriate gear and fluid pressures to apply. This is based on various input factors such as vehicle speed, engine load, throttle position, and other sensor inputs. The shift table is designed by transmission engineers and programmed into the transmission control module (TCM) or the engine control module (ECM) of the vehicle. It provides a predetermined shift pattern that optimizes performance, fuel efficiency, and overall driving comfort. Shift tables can vary between different vehicle models, engine configurations, and transmission types, ensuring optimal gear changes under various operating conditions.

Adaptive learning

Adaptive learning, also known as adaptive shift control or transmission adaptive pressure, is a technology employed in modern automatic transmissions. It involves the use of sensors, algorithms, and continuous monitoring of driving conditions. This is done to dynamically adjust the shift strategy and adapt to the driver's behavior and preferences. Instead of relying solely on fixed shift tables, the transmission control module utilizes adaptive learning to fine-tune shifting patterns based on real-time inputs.

Through adaptive learning, the transmission control module can monitor factors like driver inputs (throttle position, braking, etc.), vehicle load, road conditions, and even historical data. It then analyzes this information and modifies shift points, shift timing, and shift firmness to optimize transmission performance and responsiveness. The goal is to deliver smoother shifts, improved fuel efficiency, and a better overall driving experience. This is done by adapting to transmission wear, driving habits, and specific driving conditions encountered.

How does the control module learn?

As you can see in my simplified table below there are TAP cells listed, each cell represents engine load with 4 being the lowest and 16 being the highest. This is GM's Transmission Adaptive Pressure (TAP cell) model.

This works very similarly to fuel trims tables that the engine uses. When the table is reset, all the values start at zero. There is a range of positive 30 and negative 30. A positive number adds pressure and a negative removes pressure. As mentioned above the adjustment is dynamic, the next time a shift is made in a particular cell, it will adjust the pressure, and measure the results in the time it takes to complete the shift.

It's worth noting that different automakers may use their own terminology or specific brand names for this type of system. So, while the general concept of adaptive pressure for optimized gear shifting is still prevalent, the specific implementation and naming may vary across different vehicle manufacturers.

Why this is of importance to you can be summarized in a couple of scenarios.

Scenario One

The customer has a vehicle that is driven by multiple drivers; one driver is younger and races away from every stop sign and comes to a fast stop at every light, and the other driver is an easygoing highway driver that doesn't make many stops during their commute. Because the easygoing driver is mostly on the highway and the vehicle doesn't make many shifts during that commute, most shifts happen under heavy throttle conditions. The adaptive table will get aggressive, and the easygoing highway driver will get some uncomfortable shifts until the controller can learn and adjust to that driving style. Vice versa the aggressive driver will notice soft/lazy shifts until the controller learns and adapts to their driving habits.

Scenario Two 

A customer towed their vehicle to your shop because their transmission failed after 180,000 miles. It has been slipping for months and the fluid is black. Because everything is worn out you decide to install a remanufactured transmission instead of attempting a repair. After installation, you take the vehicle on a road test and notice something is not right. It slams on all shifts, and delays into gear. The first thing that comes to mind is that someone messed up the build on this transmission. When in reality, the computer is still using the adaptive tables it built for the old worn-out transmission you took out. 

In scenario one there is no fix needed, the vehicle is operating as designed, but how do you determine this? Unfortunately, the only way to know for sure is to ride with the customer and question them about their driving style and others that use the vehicle. Once you determine this is the case, you will need to educate the customer.

Scenario two is much easier to remedy. What we need to do is clear the adapts and start the adaptive process with the newly installed transmission. 

Clearing adaptive learn

Clearing codes and KAM

Earlier systems were very simple, to clear the adapts, simply clear any trouble codes, and erase the Keep Alive Memory (KAM). Erasing the KAM could be done by leaving the battery disconnected for 20 minutes or more.

Reset shift adaptive with a scan tool

Newer adaptive systems may require that you use some type of scan tool that gives you access to clear the adaptive strategy. Most of your aftermarket scan tools and certainly the manufacture-specific tool can clear the adapts. Again, start with clearing any and all codes IN ALL MODULES! Manufacturers can be tricky about what codes may and may not prevent adaptive learning. If codes are present, it is possible that adaptive learning is paused until the code is remedied. This is something to consider if you continue to have shift-feel issues after clearing the adapts.

Starting adaptive learn

Once you have cleared the adapts there are some steps to take that will help quicken the relearning process. Start with your scan tool, look in "service functions" or "special tests" for something labeled "quick learn" or "fast learn". Once you select the test the scan tool will prompt you with instructions to complete the test. Then move on to garage shifts. Garage shifts are done manually, see the steps below.

Garage shifts

1. With the engine running and the vehicle in park, verify the ATF is above 86°F.
2. With the engine at idle, shift from REVERSE to DRIVE and leave the shift lever in DRIVE for 5 seconds. After 5 seconds, shift back to REVERSE and leave the shift lever in REVERSE for 5 seconds. Perform this procedure 10 times - (R to D to R to D, etc.). The shift transitions must be made directly between DRIVE and REVERSE with a momentary pause in neutral.
3. With the engine at idle, shift from NEUTRAL to DRIVE and leave the shift lever in DRIVE for 5 seconds. Perform this procedure 10 times.
4. With the engine at idle, shift from NEUTRAL to REVERSE and leave the shift lever in REVERSE for 5 seconds. After 5 seconds, shift back to NEUTRAL and leave the lever in NEUTRAL for 5 seconds. Perform this procedure 10 times.

Once you have completed the garage shifts, run the vehicle on the lift or on jack stands with the drive wheels off the ground so there is no load on the drivetrain. Put the shifter in DRIVE and accelerate, letting the transmission shift through all its gears.

*Note some vehicles will not upshift due to the non-drive wheels not spinning. If this is the case move on to drive cycle adapts.

Drive cycle adaptive learn

Take the vehicle out on a road test and complete a series of shifts, this should be done when the transmission fluid is cold and warm.

• Cold (under 120°F) and complete light throttle upshifts, count each shift and make sure you achieve each upshift including torque converter lock up, coming to a complete stop at the end of each series of upshifts. Repeat this 5 times.
• Warm fluid temperature 160°F or more, complete light throttle and medium throttle upshifts. Repeat 5 times for both.

*Note, If you find one shift that is noticeably worse than the others make note of that shift and try to duplicate that condition several times until it improves. For instance, if you notice a 3-4 flair under a certain throttle, try to recreate the same conditions, until the shift improves (It should improve within one or two series of shifts). Also, check the "service functions" menu in your scan tool for a "clutch learn" on the affected clutch.

In summary

Transmission shift tables are pre-programmed tables that determine the gear shifting patterns based on predetermined parameters, while adaptive learning is a dynamic process that adjusts the shift strategy in real-time based on sensor inputs and historical data to optimize transmission performance and tailor it to the driver's behavior, driving conditions, and transmission wear.