DTC P0780: Problem in Shift Control System: General Description

The shift control system controls shifts based on gear position and on the map previously stored in the engine control module (ECM) memory. The shift control system is also designed to activate the CVT drive pulley pressure control valve and the CVT driven pulley pressure control valve according to the vehicle speed and the throttle position so the engine speed becomes equal to the target value. The pulley hydraulic pressure in the low and high pressure circuits is applied via pulley control valves A and B, and differential pressure between the low and high pressure at each of the drive and driven pulleys is generated. By changing the pulley ratio by the differential pressure, the shift control system gives feedback of the difference between the target and actual engine speed. It supplies high hydraulic pressure to the driven pulley and increases the driven pulley belt diameter when shifting to a lower ratio. It supplies high hydraulic pressure to the drive pulley and increases the drive pulley belt diameter when shifting to a higher ratio.

If the difference between the target engine rpm and the actual engine rpm is a specified value or more and this condition continues for a set time or more, a malfunction is detected and a DTC is stored.