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3.2.3 TRANSMISSION CONTROL
The 45RFE/545RFE electronic transmission has a fully adaptive control system. The system per- forms its functions based on continuous real-time sensor feedback information. The control system automatically adapts to changes in engine performance and friction element variations to provide consistent shift quality. The control system ensures that clutch operation during upshifting and down- shifting is more responsive without increased harshness.
The Powertrain Control Module (PCM) continuously checks for electrical problems, mechanical problems, and some hydraulic problems. When a problem is sensed, the PCM stores a diagnostic trouble code (DTC). Some of these codes cause the transmission to go into ‘‘limp-in’’or ‘‘default’’mode. The 45RFE/545RFE has three default modes:
(I) Immediate shutdown
- The PCM de- energizes the transmission control relay. This causes the transmission system to immediately default to third gear if shift lever is in the ‘‘D’’ position, or 2nd gear if it is in the ‘‘2’’ or ‘‘L’’ positions. Park, Neutral, and Reverse are still available.
(O) Orderly Shutdown- If the PCM recognizes a
problem that does not require an immediate shut- down, the transmission will maintain the current gear and the transmission control relay will remain energized until de-energizing it will not overspeed the engine. When the vehicle speed reaches a rea- sonable level the PCM de-energizes the transmission control relay. This causes the transmission system to immediately default to third gear if shift lever is in the ‘‘D’’position, or 2nd gear if it is in the ‘‘2’’or ‘‘L’’positions. Park, Neutral, and Reverse are still available.
(L) Logical Shutdown with Recovery- The
PCM does not de-energize the Transmission Control Relay. Instead, the transmission will utilize 1st and 3rd gears while in ‘‘D’’, and will use 2nd while in ‘‘2’’ or ‘‘L’’. All transmission operation in this mode will be at a preset line pressure (open loop). The trans- mission will resume normal operation (recover) if the detected problem goes away. Three recoveries are permitted in a given key, after the fourth occurrence the operation described above will be maintained.
Once the DRBIII is in the ‘‘EATX’’portion of the
diagnostic program, it constantly monitors the
PCM to see if the system is in limp-in mode. If the transmission is in limp-in mode, the DRBIII will flash the red LED.
126.96.36.199 TRANSMISSION OPERATION AND SHIFT SCHEDULING AT VARIOUS OIL TEMPERATURES
The transmission covered in this manual has unique shift schedules depending on the temperature of the transmission oil. The shift schedule is modified to extend the life of the transmission while operating under extreme conditions.
The oil temperature is measured with a Temperature Sensor on the 45RFE/545RFE transmission. The Temperature Sensor is an integral component of the Transmission Range Sensor (TRS). If the Temperature Sensor is faulty, the transmission will default to a ‘‘calculated’’ oil temperature. Oil temperature will then be calculated using engine cool- ant temperature, battery/ambient temperature, and engine off time from the Body Control Module (BCM). These inputs are received from the communication bus periodically and are used to initialize the oil temperature at start up. Once the engine is started, the PCM updates the transmission oil temperature based on torque converter slip speed, vehicle speed, gear, and engine coolant temperature to determine an estimated oil temperature during vehicle operation. Vehicles using ‘‘calculated oil temperature’’track oil temperature reasonably accurately during normal operation. However, if a transmission is overfilled, a transmission oil cooler becomes restricted, or if a customer drives aggressively in low gear, the calculated oil temperature will be inaccurate. Consequently the shift schedule selected may be inappropriate for the current conditions.
188.8.131.52 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 pres- sure 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.
Typical Line Pressure problems include:
Mechanical and ‘‘actual’’readings both less than desired
- If the mechanical and ‘‘actual’’readings do not increase significantly as engine speed is raised above 2000 RPM, the pressure control solenoid is usually at fault. The pressure control solenoid is usually accompanied by DTCs P0867(C8) and P0868(C9). The PCS is located in the Transmission Solenoid/TRS assembly.
- If the mechanical and ‘‘actual’’ readings vary with engine speed (above 2000 RPM), the fault is often a sticking main regulator valve. This valve is located in the transmission pump assembly.
‘‘Actual’’reading on the DRBIII differs from the Mechanical Pressure reading (higher or lower) by more than 69kPa (10 PSI). This is sometimes accompanied by a DTC P0869(CB). The fault is usually in the Line Pressure Sensor or the Line Pressure Sensor Wiring.
All three readings match, but the ‘‘actual’’reading exhibits momentary intermittent pressure increases to 1724 kPa (250 PSI). The line Pressure Sensor is usually the problem. This will cause erratic shift quality (particularly a harsh 3-1 coast down shift), repair by replacing the Line Pressure Sensor.