Line Pressure Control

LINE PRESSURE CONTROL
Proper control of the transmission line pressure is essential for proper operation. The 45RFE/ 545RFE normally uses closed loop line pressure control, where actual line pressure (reported by the line pressure sensor) is continuously monitored. The PCM determines the desired (target) line pressure which is required, and adjusts the Pressure Control Solenoid (PCS) until the actual line pressure matches the desired line pressure value. In the event of a line pressure sensor failure DTC P0932(CA), the PCM changes to an open loop control at an essentially constant line pressure.

Proper diagnosis of line pressure systems is facilitated by the use of a special tool (T-fitting - Miller # 8259) which allows the use of a mechanical pressure gauge to compare the line pressure sensor reading on the DRBIII to the gauge pressure. Technicians should compare the mechanical gauge reading with the "actual" and "desired" line pressure reading on the DRBIII. All three readings should closely match in pressure. Because the mechanical and actual line pressure may not match the desired at low engine speeds (due to low pump output rpm), line pressure should always be checked at 1500 - 2000 rpm.