DTC P0780: Problem in Shift Control System: General Description

Shift valve D is installed in the control circuit in the transmission. When the shift lever is in D range, shift valve D supplies clutch pressure control A pressure (CPC A pressure) to the 4th clutch. When the shift lever is in 1st range, shift valve D supplies clutch pressure control B pressure (CPC B pressure) to the 1st/1st-hold clutch. Shift valve D supplies CPC A pressure to the 4th clutch by increasing the line pressure and CPC A pressure. Shift valve D supplies clutch pressure control B pressure (CPC B pressure) to the 1st/1st-hold clutch which is regulated by the shift valve D spring which decreases the line pressure and CPC A pressure. The powertrain control module (PCM) monitors the mainshaft speed and countershaft speed at the gear change determined by the shift schedule. When an improper ratio is output with the predetermined gear change mode, shift valve D is stuck closed and a DTC is stored.