The shift solenoid is attached to the valve body and is positioned inside the oil valve. Gear engagement and shift are controlled by the shift solenoid. The shift solenoid is controlled electronically by the vehicle’s engine control module or transmission control module.
When electrical impulses are supplied to the proper shift solenoid, the solenoid valve opens. The opening permits transmission fluid to pass to the selected gear’s bands and clutch. The bands and clutches are able to engage the gear because of the pressured fluid. Delay shifts, no downshifts or unmanageable downshifts, and unpredictable shifts are all common signs of a defective shift solenoid.