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 |
The PCM maintains information for the following transmission adaptive systems:
Upshift Adapts (1-2, 2-3 and 3-4)
The PCM monitors the automatic transmission input speed sensor (ISS) and the vehicle speed sensor (VSS) in order to determine when an upshift has started and completed. The PCM measures the time for the upshift. If the upshift time is longer than a calibrated value, then the PCM will adjust the current to the pressure control (PC) solenoid valve to increase the line pressure for the next shift in the same torque range. If the upshift time is shorter than the calibrated value, then the PCM will decrease the line pressure for the next shift in the same torque range.
Steady State Adapts
The PCM monitors the ISS sensor and the VSS after an upshift in order to determine the amount of clutch slippage. If excessive slippage is detected, then the PCM will adjust the current to the PC solenoid valve in order to increase the line pressure to maintain the proper gear ratio for the commanded gear.
The TAP information is divided into 13 units, called cells. The cells are numbered 4 through 16. Each cell represents a given torque range. TAP cell 4 is the lowest adaptable torque range and TAP cell 16 is the highest adaptable torque range. It is normal for TAP cell values to display zero or negative numbers. This indicates that the PCM has adjusted line pressure at or below the calibrated base pressure.
Clearing Transmission Adaptive Pressure (TAP)
Updating TAP information is a learning function of the PCM designed to maintain acceptable shift times. It is not recommended that TAP information be reset unless one of the following repairs has been made:
| • | Transmission overhaul or replacement |
| • | Repair or replacement of an apply or release component - clutch, band, piston, servo |
| • | Repair or replacement of a component or assembly which directly affects line pressure |
Resetting the TAP values using a scan tool will erase all learned values in all cells. As a result, the PCM will need to relearn TAP values. Transmission performance may be affected as new TAPs are learned. The PCM must also relearn TAP values when the PCM or the transmission is replaced.
