– Dirty transmission fluid
– Faulty shift solenoid ‘A’ valve
– Shift solenoid ‘A’ valve harness or connectors
– Shift solenoid ‘A’ valve circuit is open or shorted
– Transmission will not shift gears.
Shift solenoid valve A 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.