When operating conditions are appropriate, the TCM de-energizes the 1-2, 2-3, reverse shift solenoid valve assembly (S3) to shift the transmission into Fourth gear. The manual valve remains in the DRIVE (D) position and line (2) pressure continues to feed the drive (19) fluid circuit.
The 1-2, 2-3, reverse SS valve assembly is de-energized, allowing fluid pressure to build-up in the S3 signal (16) fluid circuit.
S3 signal (14) fluid is routed to the U2 shift valve and shifts the valve against spring force to the applied position. This allows servo feed (44) fluid to pass into the 4-5 clutch (40) fluid circuit.
4-5 clutch (40) fluid is routed to the 4-5 clutch piston to apply the 4-5 clutch plates.
4-5 clutch (40) fluid is also routed through orifice #28 to the B4 release valve and shifts the valve against spring force to the applied position.
When the U2 shift valve shifts to the applied position, 3rd gear band apply (46) fluid and servo apply (45) fluid exhaust through the valve allowing the 3rd gear band servo piston assembly and the 3rd gear band assembly to release.
Exhausting 3rd gear band apply (46) fluid seats the reverse shift restrict ball check valve against the servo release (43) fluid passage and enters the servo apply (45) fluid passage.
Servo apply (45) fluid is routed to the U2 shift valve where it exhausts
With the U2 shift valve in the applied position, S4 signal (17) fluid passes through the valve into the 45 enable (51) fluid circuit.
45 enable (51) fluid is routed to the solenoid relay valve and replaces exhausting 3rd gear band apply (46) fluid to hold the valve in the released position. With the solenoid relay valve in the released position, lock up control (12) fluid is allowed to enter the TCC signal (13) fluid circuit. TCC signal (13) fluid is routed through the lock up relay valve and on to the lock up control valve in preparation for a possible torque converter clutch apply.
Direct clutch feed 2 (28) fluid is routed to the M2 shift valve where it is blocked by the valve in preparation for an upshift to fifth gear.