Functional Operation
FUNCTIONAL OPERATIONThe 45RFE Electronic Transmission has a fully adaptive control system. The system performs 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 downshifting is more responsive without increased harshness.
The Transmission Control Module (TCM) continuously checks for electrical problems, mechanical problems, and some hydraulic problems. When a problem is sensed, the TCM stores a diagnostic trouble code (DTC). Some of these DTCs cause the transmission to go into "limp-in" or "default" mode.
The 45RFE has three default modes:
(I) Immediate shutdown - The TCM 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 TCM recognizes a problem that does not require an immediate shutdown, 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 reasonable level the TCM 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 TCM 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 transmission 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(R) is in the "EATX" portion of the diagnostic program, it constantly monitors the TCM to see if the system is in limp-in mode. If the transmission is in limp-in mode, the DRBIII(R) will flash the red LED.
The 233/244 Electronic Transfer Case a desired range is selected with the switch, the shift motor moves the transfer case into the selected range.
The Transfer Case Mode Sensor tells the Transfer Case Control Module (TCCM) what range the transfer case is in.
The 233 Electronic Transfer Case has four operational ranges: 2 WD, 4 HI, 4 LO and Neutral and the 244 Electronic Transfer Case and has four operational ranges: AWD, 4 HI, 4 LO and Neutral.
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 transmission. The Temperature Sensor is an integral component of the Transmission Range Sensor (TRS). If the Temperature Sensor is faulty, (DTC P1799) the transmission will default to a "calculated" oil temperature. Oil temperature will then be calculated using engine coolant 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 TCM 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 accurate 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. The key highlights of the various shift schedules are as follows:
Extreme Cold: Oil temperature below - 16°F
Goes to "Super Cold" schedule above - 12°F oil temperature
Park, Reverse, Neutral and 1st and 3rd gear only
No Torque Converter Clutch engagement
Super Cold: Oil temperature between - 12°F and 10°F
Goes to "Cold" schedule above 10°F oil temperature
Delayed 2-3 upshift
Delayed 3-4 upshift
Early 4-3 coastdown shift
Early 3-2 coastdown shift
No 3-1 coastdown or kickdown
High speed 4-2, 3-2, 2-1 kickdown shifts are prevented
No Torque Converter Clutch engagement
Cold: Oil temperature between 10°F and 36°F
Goes to 'charm" schedule above 40°F oil temperature
Shifts at higher throttle openings will be early
High speed 4-2, 3-2, 2-1 kickdown shifts are prevented
Delayed 3-4 upshift
Early 4-3 coastdown shift
No Torque Converter Clutch engagement
Warm: Oil temperature between 36°F and 80°F
Normal operation (upshift, kickdown, and coast-down)
No Torque Converter Clutch engagement
Hot (Normal operation): Oil temperature at start up between 80°F and 240°F
Goes to "Overheat" schedule above 240°F oil temperature
Normal operation (upshift, kickdown, and coast-down)
Normal Torque Converter Clutch engagement operation
Overheat: Oil temperature above 240°F or engine coolant temperature above 244°F
Goes to "Hot" below 230°F oil temperature or "Super Overheat" above 240°F oil temperature
Delayed 2-3 upshift (26 - 32 MPH)
Delayed 3-4 upshift (41 - 48 MPH)
3rd gear FEMCC from 30 - 48 MPH
3rd gear PEMCC from 27 - 31 MPH
Super Overheat: Oil temperature above 260°F
Goes back to "Overheat" below 240°F oil temperature
All "Overheat" shift schedules features apply
2nd gear PEMCC above 22 MPH
Above 22 MPH the torque converter will not unlock unless the throttle angle is less than 4 degrees (i.e. at 50 MPH a 4th FEMCC to 3rd FEMCC shift will be made during a part throttle kickdown or a 4th FEMCC to 2nd PEMCC shift will be made at wide open throttle) or if a wide open throttle 2nd PEMCC to 1 kickdown is made.
Causes for operation in the wrong temperature shift schedule:
Extreme Cold or Cold shift schedule at start up:
Temperature Sensor or circuitry.
Overheat or Super Overheat shift schedule after extended operation:
Operation in city traffic or stop and go traffic
Engine idle speed too high - Stuck AIS motor
Aggressive driving in low gear
Trailer towing in OD gear position (use "3" position if frequent shifting occurs)
Cooling system failure causing engine to operate over 230°F
Engine coolant temperature stays low too long - If engine coolant temperature drops below 150°F, the transmission will disengage EMCC. Extended operation with the EMCC disengaged will cause the transmission to overheat.
Brake switch or circuitry. The TCM disengages the TCC when it receives a signal from the PCM that the brake has been depressed. A defective brake switch or circuitry will cause the EMCC to disengage. Extended operation with the EMCC disengaged will cause the transmission to overheat.
Transmission fluid overfilled
Transmission cooler or cooler lines restricted
Engine cooling fan inoperative
Temperature Sensor or circuitry.