Advanced Diagnostics

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 and 5th 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 and 5th 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 input shaft (mainshaft) speed and output shaft (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.




Monitor Execution, Sequence, Duration, DTC Type, OBD Status




Enable Conditions

Malfunction Threshold
The transmission is down shifted from 3rd gear to 2nd gear against the 3rd -> 4th gear upshift command.

Driving Pattern
Start the engine, and accelerate the vehicle until the transmission shifts into 5th gear in D position.

- Drive the vehicle in this manner only if the traffic regulations and ambient conditions allow.

Diagnosis Details

Conditions for illuminating the MIL
When a malfunction is detected during the first drive cycle, a Temporary DTC is stored in the PCM memory. If the malfunction recurs during the next (second) drive cycle, the MIL comes on and the DTC and the freeze frame data are stored.

Conditions for clearing the MIL
The MIL will be cleared if the malfunction does not recur during three consecutive trips in which the diagnostic runs.

The MIL, the DTC, the Temporary DTC, and the freeze frame data can be cleared by using the scan tool Clear command or by disconnecting the battery.