This month we will be looking at pressure troubles of a different kind the sort related to Dodge and Jeep vehicles with the RFE family of transmissions. We’ll look at how they control pressure through the pressure control solenoid, and discuss some common issues and how to troubleshoot line pressure related DTCs. Let’s start by examining how the pressure control solenoid affects pressure on this transmission: #LCATION MOPAR DODGE RAM PRESSURE SENSOR 545RFE TRANSMISSION HOW TO# The TCM uses the line pressure solenoid and the line pressure sensor to control pressure in this transmission. The line pressure solenoid is a variable force-type solenoid and is an integral part of the solenoid pack. The TCM controls the variable force solenoid by increasing or decreasing the duty cycle to obtain the pressure necessary. When duty cycle is at its lowest range (5% or solenoid off) pressure rises to maximum. When duty cycle is at its highest range (65% or solenoid on) pressure drops to minimum. The line pressure sensor creates a signal based on the transmission line pressure, which the TCM uses to monitor that pressure. Let’s take a closer look at line pressure control by examining a partial hydraulic diagram (figure 1). The line pressure solenoid directs oil to the end land of the pressure regulator valve. There’s no oil at the spring side of the pressure regulator valve. This means that, when commanded duty cycle is high, more pressure reaches the pressure regulator valve through the pressure solenoid, reducing line pressure. When duty cycle is low, less pressure reaches the pressure regulator valve through the pressure solenoid, increasing line pressure. Now let’s look at the pressure sensor (figure 2). The line pressure sensor receives a 5-volt reference signal from the TCM and a sensor ground. It provides a line pressure sensor signal to the TCM that varies in voltage based on line pressure. When line pressure is low, the line pressure sensor signal voltage will also be low. As line pressure increases, so will the signal voltage. The line pressure sensor voltage signal should always be between 0.35 and 4.75 volts. If voltages fall outside of these parameters, it indicates a wiring issue or a faulty sensor and the TCM will set DTC P0934 or P0935. IMPORTANT: Always refer to the factory wiring diagram for the vehicle you’re working on to avoid wire color and terminal number discrepancies. The diagnostic trouble codes most frequently associated with these transmissions are: P0868 - Line Pressure Low Now that we see how pressure operates inside the transmission and how the line pressure solenoid and sensor work, we can use that to help diagnose some of the line pressure-related codes that occur with these transmissions. When Monitored: Continuously while driving in all forward gears. Set Condition: If actual line pressure is more than 10 PSI below desired line pressure. P0933 - Hydraulic Pressure Sensor Range/Performance Set Condition: If actual line pressure is greater than the highest desired line pressure ever used in the current gear, while the pressure control solenoid duty cycle is at or near maximum (which should result in minimum line pressure). When Monitored: Continuously with the engine running and the transmission in gear. Set Condition: If actual line pressure is more than 172.4 kPa (25 PSI) higher than the desired line pressure, but less than the highest line pressure ever used in the current gear. When Monitored: Continuously with the engine running. P0935 - LINE PRESSURE SENSOR CIRCUIT HIGH Set Condition: If line pressure sensor voltage is less than or equal to 0.35 volts for 0.18 seconds. Set Condition: If line pressure sensor voltage is greater than or equal to 4.75 volts for 0.18 seconds. When line pressure is low, the sensor signal voltage should be low, and when line pressure is high, sensor signal voltage should be high.When the line pressure solenoid is on (high duty cycle), line pressure should be low, and when the line pressure solenoid is off (low duty cycle), line pressure should be high.Now, how do we best diagnose them? Here’s what we know: So those are the codes and their definitions. #LCATION MOPAR DODGE RAM PRESSURE SENSOR 545RFE TRANSMISSION HOW TO#.
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