Solenoids

DESCRIPTION
Solenoids are used to control the L/R, 2/4, OD, and UD friction elements. The reverse clutch is controlled by line pressure from the manual valve in the valve body. The solenoids are contained within the Solenoid and Pressure Switch Assembly, and cannot be serviced individually. They can only be serviced by replacing the assembly.


OPERATION
The solenoids receive electrical power from the Transmission Control Relay through a single wire. The Transmission Control Module (TCM) energizes or operates the solenoids individually by grounding the return wire of the solenoid needed. When a solenoid is energized, the solenoid valve shifts, and a fluid passage is opened or closed (vented or applied), depending on its default operating state. The result is an apply or release of a frictional element.
The 2/4 and UD solenoids are normally vented to allow transaxle limp-in (P,R,N,2) in the event of an electrical failure.
The continuity of the solenoids and circuits are periodically tested. Each solenoid is turned on or off depending on its current state. An inductive spike should be detected by the TCM during this test. It no spike is detected, the circuit is tested again to verify the failure. In addition to the periodic testing, the solenoid circuits are tested if a speed ratio or pressure switch error occurs.