RAM 1500 Truck 4WD V8-5.9L VIN Z (2002)
Fluid Pressure Sensor/Switch: Description and Operation
45RFE 4 Speed
45RFE - AUTOMATIC TRANSMISSION
Line Pressure (LP) Sensor / DESCRIPTION
The TCM utilizes a closed-loop system to control transmission line pressure. The system contains a variable force style solenoid, the Pressure Control
Solenoid, mounted on the side of the solenoid and pressure switch assembly. The solenoid is duty cycle controlled by the TCM to vent the unnecessary
line pressure supplied by the oil pump back to the sump. The system also contains a variable pressure style sensor, the Line Pressure Sensor, which is a
direct input to the TCM. The line pressure solenoid monitors the transmission line pressure and completes the feedback loop to the TCM. The TCM uses
this information to adjust its control of the pressure control solenoid to achieve the desired line pressure.
OPERATION
The TCM calculates the desired line pressure based upon inputs from the transmission and engine. The TCM calculates the torque input to the
transmission and uses that information as the primary input to the calculation. The line pressure is set to a predetermined value during shifts and when
the transmission is in the PARK and NEUTRAL positions. This is done to ensure consistent shift quality. During all other operation, the actual line
pressure is compared to the desired line pressure and adjustments are made to the pressure control solenoid duty cycle.
