Shift Solenoid Valves: 1-2 & 2-3

The shift solenoid valves are two identical, electronic exhaust valves that control upshifts and downshifts in all forward gear ranges. These valves are normally open. These shift solenoid valves work together in a combination of ON and OFF sequences to control the positions of the 1-2, 2-3, and 3-4 shift valve trains. The Powertrain Control Module (PCM) monitors numerous inputs to determine the appropriate solenoid state combination and transmission gear for the vehicle operating conditions.

The solenoid states are normally ON (1-2) and OFF (2-3) in the Park, Reverse, and Neutral gears. However, these may change based on the vehicle speed and the throttle position. The PCM energizes the shift solenoid valves by providing a ground to the solenoid's electrical circuit. This sends current through the coil winding of the solenoid, thereby creating a magnetic field. The magnetic field repels the plunger inside the solenoid. This seats the solenoid metering ball against the fluid inlet port. This action prevents the exhaust of fluid through the solenoid. It then provides an increase in fluid pressure at the end of the shift valves. This fluid pressure initiates an upshift by moving the shift valves. See appropriate OIL CIRCUIT DIAGRAMS in HYDRA-MATIC 4T40-E/4T45-E article in TRANSMISSIONS for a complete description of the hydraulic control of the shift valves for each gear range.

The resistance on the shift solenoid valves should measure between 19-24 ohms when measured at 68°F (20°C) and between 24-31 ohms when measured at 190°F (88°C). The shift solenoid valves should energize when the voltage is greater than 7.5 volts. The shift solenoid valves should de-energize when the voltage is less than one volt.