Performance Shift Algorithm (PSA)

This vehicle is equipped with a Performance Shift Algorithm (PSA) feature. This feature allows the vehicle to sense high performance handling maneuvers by monitoring inputs to the Powertrain Control Module (PCM). These inputs include the Throttle Position (TP) sensor, Vehicle Speed Sensor (VSS), lateral accelerometer, and extended travel brake switch. PSA 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, PSA 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. PSA is designed so that it does not activate in-city or highway-type driving. When PSA does activate, drivers may feel the transmission shift, as well as hear the engine rev. This condition will remain until PSA deactivates. PSA could enable during non-high performance maneuvers if the lateral accelerometer fails or gets loose. This would result in delayed or erratic shift patterns. The lateral accelerometer has Diagnostic Trouble Codes (DTCs), which can be found in the Antilock Brake System (ABS) with Traction Control System (TCS) and Integrated Chassis Control System (ICCS) section. 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 PSA or a faulty accelerometer.