Transmission General Description

Transmission General Description
The 4T80-E is a fully automatic front wheel drive electronically controlled transmission. The 4T80-E provides four forward ranges including overdrive. The PCM controls shift points by means of two shift solenoids. Three gear-type oil pumps supply the oil pressure. The PCM regulates oil pressure by means of a transmission pressure control solenoid. The PCM controls the shift schedule and the TCC apply rates. Many sensor inputs also influence the shift schedule and the TCC apply rates.
You can operate the transmission in any one of the following seven modes:
- P - Park position prevents the vehicle from rolling either forward or backward. For safety reasons, use the parking brake in addition to the park position.
- R - Reverse allows the vehicle to be operated in a rearward direction.
- N - Neutral allows the engine to be started and operated while driving the vehicle. If necessary, you may select this position in order to restart the engine with the vehicle moving.
- OD - Overdrive is used for all normal driving conditions. Overdrive provides four gear ratios plus a converter clutch operation. Depress the accelerator in order to downshift for safe passing.
- D - Drive position is used for city traffic and hilly terrain. Drive provides three gear ranges. Depress the accelerator in order to downshift.
- 2 - Manual second provides acceleration and engine braking.
- 1 -Manual Lo provides maximum engine braking.

Performance Algorithm Shifting (PAS)
The Seville STS is equipped with a Performance Algorithm Shifting (PAS) feature. This feature allows the vehicle to sense high performance handling maneuvers by monitoring inputs to the PCM. These inputs include the throttle position sensor, vehicle speed sensor, lateral accelerometer, and extended travel brake switch. PAS enables only during maneuvers which involve sufficiently aggressive cornering. It provides performance-oriented shifting of the transmission without the need for the driver to shift the gear selector manually or command downshifts with the throttle. For the most aggressive driving, the lowest gear allowable for the vehicle's speed is commanded at all times. Less aggressive driving results in less aggressive gear selection. Upshifts and downshifts occur automatically as vehicle speed changes. When the driver returns to a non-aggressive driving mode, like straight-line driving with only mild throttle and brake inputs, PAS disables and the transmission shifts normally. The time it takes to disable is generally less than one second, although it can be somewhat longer if the driver is still braking, accelerating or cornering. PAS is designed so that it does not activate in-city or highway-type driving. When PAS does activate, drivers may feel the transmission shift, as well as hear the engine rev. This condition will remain until PAS deactivates. PAS could enable during non-high performance maneuvers if the lateral accelerometer fails or gets loose. This would result in delayed or erratic shift patterns. If the lateral accelerometer related codes (C1284 and C1285) are not set, and the accelerometer is securely mounted, then delayed or erratic shift patterns in normal driving probably are not caused by PAS or a faulty accelerometer.