RAM 1500 Truck 2WD V8-4.7L (2008)
Overdrive Solenoid: Description and Operation
42RLE Automatic Transmission
Description
DESCRIPTION
The Solenoid/Pressure Switch Assembly (1) is inside the transmission and mounted to the valve body assembly. The assembly consists of four solenoids
that control hydraulic pressure to the L/R, 2/4, OD, and UD friction elements (transmission clutches), and the torque converter clutch. The reverse clutch
is controlled by line pressure from the manual valve in the valve body. The solenoids are contained within the Solenoid/Pressure Switch Assembly, and
can only be serviced by replacing the assembly.
The solenoid assembly also contains pressure switches that monitor and send hydraulic circuit information to the TCM. Likewise, the pressure switches
can only be service by replacing the assembly.
Operation
OPERATION
SOLENOIDS
The solenoids receive electrical power from the Transmission Control Relay through a single wire. The 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 applied, which allows fluid to pass through in their relaxed or "off" state. By design, this allows transmission
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. If 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.
PRESSURE SWITCHES
The 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 range for the pressure switch closing and opening points is 11-23 psi. Typically
the switch opening point will be approximately one psi lower than the closing point. For example, a switch may close at 18 psi and open at 17 psi. The
switches are continuously monitored by the TCM for the correct states (open or closed) in each gear as shown in the following chart:
