Grade Logic Control System

The TCM compares actual driving conditions with driving conditions memorized in the TCM, based on input signals from Vehicle Speed Sensor (VSS), Throttle Position (TP) sensor, engine coolant temperature sensor, brakelight switch signal and A/T gear position switch. The TCM uses these input signals to control shifting while vehicle is ascending or descending a slope or during deceleration.

When TCM determines vehicle is ascending a slope with shift lever in "D4" position, the TCM extends engagement of 3rd gear to prevent transaxle from frequently shifting between 3rd and 4th gears to provide smooth vehicle operation. Shift points between 3rd and 4th gear are stored in TCM which allows the most suitable gear selection depending on conditions.

When TCM determines vehicle is descending a slope with shift lever in "D4" position, the TCM changes upshift speed from 3rd to 4th gear when throttle is fully closed. This widens the 3rd gear operating range from that programmed for level surface operation and, in conjunction with engine braking from torque converter lock-up, provides smooth vehicle operation. When vehicle is decelerating on a gradual hill in 4th gear, or when applying brakes on a steep hill, the transaxle will downshift to 3rd gear. When vehicle accelerates, transaxle will shift into 4th gear.

When vehicle decelerates from speeds greater than 27 MPH (such as entering a corner), TCM shifts transaxle from 4th gear to 3rd gear earlier than normal to reduce the number of times the transaxle shifts. This allows smoother acceleration and vehicle operation.