Solenoid and Pressure Switch Assembly

DESCRIPTION
The solenoid and pressure switch assembly is external to the transaxle and mounted to the valve body assembly. The assembly consists of four solenoids that control hydraulic pressure to four of the five friction elements (transaxle clutches), and the torque converter clutch. The solenoid assembly also contains pressure switches that feed information to the TCM.

OPERATION
The solenoids within the assembly are supplied voltage by the Transmission Control Relay. The solenoids are energized when the Transmission Control Module (TCM) grounds the return wire for the solenoid that is needed. The pressure switches simply tell the TCM whether or not pressure exists within a clutch circuit. Refer to "Pressure Switches" for more information regarding pressure switches.

BATTERY FEED (TCM)
A fused, direct battery feed to the TCM is used for continuous power. The battery feed is spliced and also fed to the contact side of the Transmission Control Relay. This battery voltage is necessary to retain adaptive learn values in the TCM's RAM (Random Access Memory). When the battery (B+) is disconnected, this memory is lost. When the battery (B+) is restored, this memory loss is detected by the TCM and a Diagnostic Trouble Code (DTC) is set.

TRANSMISSION CONTROL RELAY

Fig. 4:

The transmission control relay is located in the Power Distribution Center (PDC) on the left side of the engine compartment (Fig. 4). The relay is sup-plied fused B+ voltage, energized by the Transmission Control Module (TCM), and is used to supply power to the solenoid pack when the transmission is in normal operating mode. When the relay is "off', no power is supplied to the solenoid pack and the transmission is in "limp-in" mode. After a controller reset (ignition key turned to the "run" position or after cranking engine), the TCM energizes the relay. Prior to this, the TCM verifies that the contacts are open by checking for no voltage at the switched battery terminals. After this is verified, the, voltage at the solenoid pack pressure switches is checked. After the relay is energized, the TCM monitors the terminals to verify that the voltage is greater than 3 volts.

PRESSURE SWITCHES
The pressure switches are located inside the solenoid pack assembly and are only serviced by replacing the assembly.





The Transmission Control Module (TCM) relies on three pressure switches to monitor fluid pressure in the L/R, 2/4, and OD hydraulic circuits. The primary purpose of these switches is to help the TCM detect when clutch circuit hydraulic failures occur. The switches close at 23 psi and open at 11 psi, and simply indicate whether or not pressure exists. The switches are continuously monitored by the TCM for the correct states (open or closed) in each gear as shown in the following chart:
A Diagnostic Trouble Code (DTC) will set if the TCM senses any switch open or closed at the wrong time in a given gear.
The TCM also tests the 2/4 and OD pressure switches when they are normally off (OD and 2/4 are tested in 1st gear, OD in 2nd gear, and 2/4 in 3rd gear). The test simply verifies that they are operational, by looking for a closed state when the corresponding element is applied. Immediately after a shift into 1st, 2nd, or 3rd gear with the engine speed above 1000 rpm, the TCM momentarily turns on element pressure to the 2/4 and/or OD clutch circuits to identify that the appropriate switch has closed. If it doesn't close, it is tested again. If the switch fails to close the second time, the appropriate Diagnostic Trouble Code (DTC) will set.