Grade Logic Control: Descending Control
When the PCM determines that the vehicle is going down a hill in D, the upshift speed from 4th to 5th gear, from 3rd to 4th gear, and from 2nd to 3rd gear (when the throttle is closed) becomes higher than the set speed for flat road driving to extend the 4th gear, 3rd gear, and 2nd gear driving conditions or modes. This, in combination with engine braking from the deceleration lock-up, achieves smooth driving when the vehicle is descending. There are three descending modes stored in the PCM with different 4th gear, 3rd gear, and, 2nd gear driving conditions or modes based on the steepness of the grade. When the vehicle is in 5th or 4th gear and the vehicle is decelerating while applying the brakes on a steep hill, the transmission downshifts to a lower gear. When you accelerate, the transmission then returns to a higher gear.