Body of Evidence
- Subject: Relearn procedures for shift adaptation
- Unit: AW55-50
- Vehicle Applications: GM, Saturn, Saab, Volvo, Nissan
- Essential Reading: Rebuilder, Diagnostician
- Author: Jeff Parlee
I feel like I have grown up with the transmission industry. The first transmission that I rebuilt was a cast-iron Powerglide that failed in my 1957 Chevy. Rebuilding that transmission successfully turned into a career.
The transmissions of the 1950s through the 1970s were mostly hydraulic. In the 1980s we were seeing more solenoids on transmissions, and in 1989 we saw the Chrysler 604.
The 604 was the first American computer-controlled transmission with adaptive shift strategy. The relearn process was not much different from what it is for today’s transmissions. For those of you who were not in the transmission industry back then, there was no quick-learn procedure for the 604. The quick-learn feature was not available until the mid-’90s. You actually had to drive the car at different throttle openings to relearn the shift adapts, and it could take 30 minutes or more of driving time to get it right.
Today’s cars are not that much different from the early 604 except that there are a couple of new wrinkles. Most of the cars today need a factory scan tool or equivalent to reset the shift adapts to zero. Very few can be reset by disconnecting the battery, but you still have to drive the vehicle to relearn the shift adapts after clearing them.
The shift adapts are used to help compensate for wear in the transmission, allowing the customer to retain the same shift feel that the car had when it was new. As the friction components and valve-body parts wear, the computer bumps up the pressure on that shift to retain the same shift feel. When the valve body is replaced or the transmission is rebuilt or replaced, the shift adapts may be high (depends on how worn the transmission was). When the shift adapts are high and the transmission/valve-body wear has been corrected, the shifts and engagements can be harsh or binding may occur. Most computers can adapt the pressures down with a lot of driving, but the process is painfully slow and some manufacturers recommend against driving the car until the shift adapts have been cleared to avoid transmission damage.
Let’s look at the AW55-50, used by GM, Saturn, Saab, Volvo and Nissan in the U.S.
- The shift adapts in the GM, Saturn and Saab can be cleared by disconnecting the battery cables, taping them together and turning on the headlamps. This will drain any power from the TCM. After about 10 minutes, reconnect the battery, start the car, allow it to get to operating temperature and clear any trouble codes.
- The Nissans and Volvos will need a factory scan tool or equivalent to clear the shift adapts. Nissan refers to clearing the shift adapts as “initializing the TCM.” The Nissan and Volvo shift adapts cannot be cleared by disconnecting the battery.
- After the shift adapts have been cleared the vehicle will need to be driven to relearn the proper shift adapts. The following is the procedure for relearning the shift adapts.
- N-D engagement adaptation: Shift from neutral to drive, wait three seconds, shift back to neutral. Repeat five times.
- N-R engagement adaptation: Shift from neutral to reverse, wait three seconds, shift back to neutral. Repeat five times.
- Upshift and downshift adaptation: In the drive position, accelerate from a stop at light throttle – about 15%-20% throttle angle – to fourth gear. Decelerate while braking lightly, using a minimum of 14 seconds to come to a full stop. Repeat five times. In the drive position, accelerate from a stop at a throttle opening of 50%-55% all the way to fifth gear. Decelerate while braking lightly so that each downshift is felt. Repeat five times.
- 2-1 downshift adaptation: With the shifter in the intermediate range, accelerate above 16 mph, release the throttle, then manually shift to low range and come to a stop. Repeat 10 times.
When performing the relearn procedure on any vehicle, remember that the transmission must be within the temperature specification for relearning to occur, and there can be no codes present or the TCM will not relearn.
The owner of the AAMCO shop in Turnersville, N.J., Richard Roth, recently told me that the shop works on a lot of Nissans with the 55-50 and he has found a procedure that works for him. He has his R&R man fill the transmission and allow the engine and transmission to get to operating temperature. The technician is instructed not to operate the transmission on the lift, just fill it. Once it’s at operating temperature, Richard drives the vehicle as instructed above and continues to drive it for 30-45 minutes until the shifts feel good. Richard says he has had to take only one vehicle to the dealer to have the shift adapts cleared since he started doing this. Richard makes the point that you have to be patient; some take longer than others to relearn.
What started out as TV linkage and vacuum modulators in the ’50s and ’60s are now sensors, solenoids and computers to perform the same tasks. I guess the only constant in this industry is change.
Jeff Parlee is director of product support at ValveBody Xpress.