The transmission control module (TCM) produces excellent shift quality by applying closed loop control that constantly adjusts shift characteristics for changes in operating conditions. These adjustments are based on vehicle conditions, such as grade, load, and engine power.
The learning process of comparing and adjusting shift parameters is referred to as adaptive control. Adaptive control establishes initial conditions for shifts and makes during shift adjustments. The TCM constantly monitors operating conditions, such as battery voltage and transmission sump temperature, and adjusts shift parameters accordingly. After a shift is completed, the TCM compares the shift to a target shift profile in the TCM calibration and makes adjustments before the next shift of the same kind is made.
The Allison 1000 Series transmission consists of 5 clutches. A combination of 2 clutches is required to be engaged, in order to attain a torque path from the input to the output of the transmission. The following table indicates the clutch combinations for each gear range.
Gear Range | 1-2-3-4 Clutch | 4-5-6 Clutch | 3rd, 5th and Reverse Clutch | 2-6 Clutch | Low and Reverse Clutch | TCC |
|---|---|---|---|---|---|---|
PARK/NEUTRAL | -- | -- | -- | -- | X | -- |
REVERSE | -- | -- | X | -- | X | -- |
First | X | -- | -- | -- | X | -- |
Second | X | -- | -- | X | -- | X |
Third | X | -- | X | -- | -- | X |
Fourth | X | X | -- | -- | -- | X |
Fifth | -- | X | X | -- | -- | X |
Sixth | -- | X | -- | X | -- | X |
The Allison 1000 Series transmission utilizes clutch-to-clutch shift control to achieve range changes. In every case, except shifts to or from NEUTRAL, 1 clutch is exhausted and another applied in order to make a range shift. The hand-off between exhausting and applying clutches is precisely controlled by the use of 2 pressure control solenoids (PCS). These solenoids are labeled PCS1 and PCS2 in the transmission. For example, to make a 1-2 shift, PCS1 is used to trim pressure off the low and reverse clutch, and PCS2 is used to trim pressure on the 2-6 clutch. The TCM modulates the current to both PCS1 and PCS2, which translates to a proportional level of pressure to the clutch. In order to make a shift, the TCM uses software and calibration settings of several program parameters in order to determine the level of current sent to the respective PCS. These parameters are referred to as adaptive values. With a new transmission and TCM calibration, the adaptive values are set to base calibration level. The transmission uses the base calibration to perform the first of each type of shift. However, once the transmission has performed a shift, the TCM evaluates the actual shift and compares it to an ideal shift in the TCM memory. Based on that comparison, the TCM changes the settings of the adaptive values to a level that it believes will result in a shift closer to the ideal shift the next time it makes that type of shift. This is referred to as adaptive shifting. When the transmission/TCM calibration is new, the TCM is in fast adaptive mode. The TCM is allowed to make large changes in the adaptive values after each shift. Once the TCM determines that a given shift is close to the ideal level, it switches to slow adaptive mode. In slow adaptive, the TCM still is evaluating shifts and changing adaptive values, but is only allowed to do so in smaller increments. When a shift switches from fast to slow adaptive mode, it is described as converged. The TCM is programmed in order to switch from fast to slow adaptive mode in as many as 15-20 shifts. It is important to understand that there are many different distinct shifts recognized by the TCM, and each of these shifts has its own adaptive values. There are upshifts and downshifts to and from each range, as well as unique adaptive values for several different throttle regions for each upshift and downshift. It may take a significant amount of time before most of the shifts converge from fast to slow adaptive, and thus it is not unusual to experience somewhat harsh or unpleasant shift quality until these shifts are adapted.
TCC engagement is accomplished by a separate PCS. There are adaptive values for this as well, and thus it will also require some driving for TCC engagement to converge.
If you are experiencing harsh shifts, it is important to verify whether the particular shift is converged. Use the scan tool in order to determine if the shift is converged.
| • | If the shift is not converged, the TCM is learning how to adapt that shift, and needs to be driven more, with the intention of performing more of the particular type of shift. |
| • | If a particular shift is converged, but still objectionable, it is good troubleshooting practice to reset the adaptive values for that shift back to base calibration level. This will automatically reset the TCM to fast adaptive mode. The vehicle should then be driven in order to allow the TCM to relearn the shift. Many times this will correct the condition. It is possible to reset individual shifts without affecting the other shifts. |
Important: WHEN REPLACING A FAILED TRANSMISSION WITH A REPLACEMENT UNIT, IT IS IMPORTANT TO RESET THE TCM IN ORDER TO BASE CALIBRATION AND FAST ADAPTIVE FOR ALL SHIFTS. This can be done in 1 step with FastLearn. If this is not done, the TCM adaptive values will be at the settings that it learned for the old transmission, and will be in slow adaptive mode. Under these conditions, it would take an unacceptably long time for the adaptive values to converge to levels suitable for the new transmission.
