For 1990-2009 cars

The 4T65-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 PCM has the ability to learn and adjust for monitored system changes.

The PCM maintains information for the following transmission adaptive systems:

1-2, 2-3, 3-4 Upshift Adapts -- The PCM monitors the automatic transmission input shaft speed (AT ISS) sensor and the vehicle speed sensor (VSS) in order to determine when the transmission has started and completed an upshift. The PCM calculates the length of time from the beginning to the completion of the upshift. If the time of the upshift was longer than a calibrated value, then the PCM will adjust the current to the 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 the calibrated value, then the PCM will adjust the current to the PC solenoid to decrease line pressure for the next (same) upshift under identical conditions.

Steady State Adapts -- The PCM monitors the AT ISS sensor and the VSS after an upshift has occurred in order to determine the amount of clutch slippage. The PCM adjusts the current to the PC solenoid in order to maintain slippage below a set amount.