Transmission Adaptive Functions: Notes

The 4L80-E transmission uses a line pressure control system that has the ability to adapt line pressure to compensate for normal wear of the following parts:

• The clutch fiber plates
• The springs and seals
• The apply bands

This adaptive feature is similar to the fuel and idle control systems, where the powertrain control module (PCM) and the transmission control module (TCM) has the ability to learn and adjust for monitored system changes.

The PCM/TCM maintains information for the following transmission adaptive systems:

1-2, 2-3, 3-4 Upshift Adapts - The PCM/TCM monitors the automatic transmission input shaft speed sensor (ISS) and the output speed sensor (OSS), to determine when the transmission has started, and completed an upshift. The PCM/TCM looks at the time from the beginning, until the completion of the upshift. If the time of the upshift was longer than a calibrated value, then the PCM/TCM adjusts the current to the transmission pressure control (PC) solenoid to increase line pressure for the next, same, upshift under identical conditions. If the time of the upshift was shorter than a calibrated value, then the PCM/TCM adjusts the current, to the transmission PC solenoid, to decrease line pressure for the next, same, upshift under identical conditions.

Steady State Adapts - Diesel only - The PCM/TCM monitors the automatic transmission ISS and the OSS after a shift has occurred, to determine the amount of clutch slippage in the transmission. If to much slippage is detected, the PCM/TCM adjusts the current, to the transmission PC solenoid, to increase the line pressure and reduce clutch slip.