Possible causes

– Low transmission fluid level
– Dirty transmission fluid
– Faulty underdrive solenoid valve
– Underdrive solenoid valve harness is open or shorted
– Underdrive solenoid valve circuit poor electrical connection

When is the code detected?

The P0755 code is detected when TCM detects an improper voltage drop when it tries to operate the solenoid valve.

Symptoms

– Engine Light ON (or Service Engine Soon Warning Light)
– Transmission will not shift gears.

P0755 KIA Description

Underdrive solenoid valve is turned ON or OFF by the Transmission Control Module (TCM) in response to signals sent from the park/neutral position (PNP) switch, vehicle speed and Engine Control Module (ECM) (throttle opening). Gears will then be shifted to the optimum position.