History is brimming with examples of people overcoming obstacles and reaching goals by altering the way they attack different problems. In baseball, hitters who can adjust to different pitching styles will consistently get more hits and help advance the base runners. On the battlefield, soldiers achieve their objectives and live to fight another day by adapting to events as they unfold; for them, failure to adapt can have serious consequences.
Transmission repair is no exception. Builders have become versatile in making mechanical modifications that restore OE operation or fend off common problems before they happen, from installing oversized valves to reinforcing drum splines to altering feed circuits.
But many technicians are unfamiliar with adaptive strategies that are part of the control mapping of the transmission control module (TCM) or powertrain control module (PCM). Failure to consider these adaptations can lead to unnecessary part replacement, never-leaves or comebacks.
Pressure regulator valves provide a good example of adaptation in action. These valves are relentlessly active, causing the valve and bore to deteriorate over time. This wear creates a path for fluid to escape the circuit, lowering (or raising) line pressure.
Using various sensors and calculations, the TCM “realizes” line pressure has strayed from specification and modifies the pulse-width signal to the pressure control solenoid, stroking the valve a little further to raise (or lower) pressure to compensate. This principle is in effect for all regulator valves, not just the main PR.
It doesn’t end with regulator valves. As bands and clutches degenerate, they take longer to apply when commanded. The TCM “notices” this and adjusts apply and release timing to maintain shift quality. In fact, there is constant monitoring and manipulation of components taking place throughout the transmission at all times. Adapting in this manner allows the TCM to provide normal operation and shift feel even as various components age and wear.
But adaptation cannot hold wear at bay forever. Eventually wear overcomes the TCM’s ability to compensate and becomes apparent to the driver in the form of harsh or soft shifting, delayed engagement and shift timing problems. When the TCM reaches the limit of its adaptation window, trouble codes will be triggered, such as GM’s “Maximum Shift Adapt” code P1811.
Adaptation can coax thousands of extra miles out of the transmission, but wear often progresses to the point where repair or rebuild is necessary.
Usually the technician suspects there is a self-inflicted wound, additional components requiring replacement or that the original diagnosis was wrong. While this could be the case, these are problems that are also commonly caused by failure to reset adaptations after repairs are performed.
Back to the pressure regulator example: If adaptations have evolved to raise pressure in compensation for a worn valve and you fix the problem, the TCM must be “informed” of the repair by resetting adaptations. Otherwise the TCM will continue controlling the transmission as though it contained a worn valve, resulting in excessive pressure and harsh shifting.
Remember that adaptation consists of small, incremental control changes in response to gradual component wear. During repair or rebuild, worn parts are instantly eliminated. It takes time for the TCM to adapt to change that radical, during which serious damage can be inflicted on the transmission. Preventing a post-build grenade from going off inside the case is a compelling reason to reset adaptations on all units that have a reset procedure.
Some are a bit more involved. Many Audi/VW models require using a scan tool in combination with shifting through gears a number of times during a test drive. Other manufacturers have similar shift progression reset schemes. Some require a simple battery reset. Some models have no reset procedure at all, adapting to new parts automatically after relatively short drive cycles.
It is important to check manufacturer-specific reference material to determine the reset procedure for the vehicle model being worked on. Notice that says vehicle model, not transmission model. This is because some transmissions—such as Aisin AW 55-50SN—are installed in a range of vehicles containing different control units. The reset procedure for a Volvo will not be the same as that for a Chevy.
It must be stated that resetting control unit adaptations and reflashing the control unit are two distinctly separate procedures with different purposes:
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