– Dirty transmission fluid
– Faulty shifting solenoid valve
– Shifting solenoid valve harness is open or shorted
– Shifting solenoid valve circuit poor electrical connection
– Transmission may not shift to the next gear.
This P0781 code indicates that the 1-2 shift valve in the valve body is locked in the direction of the spring compression. The Transmission Control Module (TCM) controls the gearshifts by turning the shift solenoid valves “ON/OFF” and switching oil pressure to the valves in the valve body. The TCM calculates the “actual” transmission gear by comparing the signals from the input speed sensor and the output speed sensor.