288 Automatic Transmissions and Transaxles Copyright by Goodheart-Willcox Co., Inc. Drive, Third Gear When the ECM decides that the transmission should be shifted into third gear, it de-energizes the 2-3 shift solenoid, Figure 12-34. The 1-2 shift solenoid remains de-energized. Trace the oil circuit pathways and you will notice that each solenoid controls the related shift valve by controlling the pressure delivered to that valve. Each one of these sole- noids operates by sending pressure to the related valve to cause it to move. Other dedicated solenoids move the shift valve by exhausting (removing) pressure already present on one side of the valve. These solenoids usually exhaust pres- sure directly to the oil pan or sump. A few dedicated sole- noids operate by directly moving the valve through linkage or by directly moving the valve. The 2-3 shift solenoid is a normally open solenoid, and oil exits through the valve when it is de-energized. AFL oil pushes the 2-3 shift valve and 2-3 shuttle valve to the right. 2nd oil can now pass through the 2-3 shift valve. This oil is renamed 3-4 SIG oil after it passes through the 2-3 shift valve. In addition to applying and releasing holding mem- bers, 3-4 SIG oil goes to the 3-2 downshift valve, 3-2 control valve, and 3-4 shift valve for later use. To apply the clutch, the 3-4 SIG oil passes through a check ball and orifice (#4). The #4 check ball and orifice restricts oil flow to the clutch piston to cushion the shift. Notice that this oil is renamed 3-4 CL (CL for clutch) oil after it passes through the #4 check ball and orifice. 3-4 CL oil is also sent to the 3-2 downshift valve and the 3-2 control valve for use during 3-2 downshifts, explained later. 3-4 CL oil also goes to the #2 check ball and orifice, then to the 2-4 servo. The oil, now called 3RD ACC oil, pressurizes the servo release passage, causing the servo to release the band. The action of the #2 check ball and orifice, and the accumulation action of the servo as it releases, cushions the shift. A separate accumulator is not used. 3RD ACC oil also goes to the 3-2 control valve for later use. With the 3-4 clutch applied by 3-4 CL oil and the band released by 3RD ACC oil, the transmission is now in third gear. Since the 2-3 shuttle valve also moves to the right when shift solenoid B is de-energized, this opens a passage for AFL oil to the spring side of the 1-2 shift valve. How this affects 1-2 shift valve operation is explained in the next section. Drive, Fourth Gear When enough speed is attained and other sensor inputs are correct, the ECM decides that the transmission should be shifted into fourth gear. The ECM energizes the 1-2 shift solenoid, sealing the exhaust passage in the solenoid. The 2-3 shift solenoid remains de-energized. See Figure 12-35. With the 1-2 shift solenoid back on, AFL oil pressure can build up on the right side of the 1-2 shift valve through the orifice above the valve (#25). Once through the orifice, the oil is renamed SIG A oil. However, the extra oil supplied by the 2-3 shuttle valve assists the spring and keeps the 1-2 shift valve from moving. The AFL oil, renamed the SIG A oil, builds up to its full value and moves the 3-4 shift valve. With the 3-4 shift valve in the upshifted position, 3-4 SIG oil, renamed 4th SIG oil in this circuit only, pushes the 3-4 relay and 4-3 sequence valves to the right. This allows 2nd oil to charge the 3-4 circuit that sends oil to the outer apply side of the servo. The outer side is an apply area that helps the 2nd clutch oil overcome release oil and spring pressure and reapply the band. Some 3-4 SIG oil is diverted to the 3-4 accumulator to improve shift feel. This is renamed 3-4 ACC oil. Converter Clutch Application The converter clutch apply is shown in Figure 12-35. It is almost identical to the apply used on the nonelectronic version of this transmission. The converter clutch can be applied in any forward gear except first. When the converter clutch signal valve is closed by 2nd oil, line pressure can reach the converter clutch valve. As long as the torque converter clutch solenoid is de-energized, this oil pressure leaks out past the internal check ball and seat. With no pressure applied to it, the valve remains in the unapplied position, and oil flows through apply and release circuits. When the torque converter clutch solenoid is ener- gized, the check ball seats and closes the passage. Oil pressure builds up and becomes high enough to move the converter clutch valve. When the valve moves, oil pressure on the lockup clutch release side is exhausted. Oil pressure remains on the clutch apply side and pushes the clutch plate into contact with the converter cover, locking the converter. Downshifts As with upshifts, the ECM determines when the trans- mission should downshift and performs the shift by ener- gizing or de-energizing the 1-2 and 2-3 solenoid. The ECM bases these decisions on engine operating conditions, vehicle speeds, and other inputs supplied by the sensors. Based on these inputs, the ECM also engages and disengages the torque converter clutch. The term downshifts refers to the normal downshifts that occur when the vehicle is brought to a stop, as well as the detent (passing gear) downshifts that occur when the throttle is suddenly depressed. To shift from fourth to third, the ECM de-energizes the 1-2 solenoid, Figure 12-36. The 2-3 solenoid remains de- energized. De-energizing the 1-2 solenoid removes pressure from the SIG A circuit and causes the 3-4 shift valve to move