Transmission Operation and Shift Scheduling

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 - 16F
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 - 12F and 10 F
Goes to "Cold" schedule above 10F 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 36F
Goes to "Warm" 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 36F and 80 F
Normal operation (upshift, kickdown, and coast-down)
No Torque Converter Clutch engagement
Hot (Normal operation): Oil temperature at start up between 80F and 240 F
Goes to "Overheat" schedule above 240F oil temperature
Normal operation (upshift, kickdown, and coast-down)
Normal Torque Converter Clutch engagement operation
Overheat: Oil temperature above 240F or engine coolant temperature above 244 F
Goes to "Hot" below 230F oil temperature or "Super Overheat" above 240 F oil temperature
Delayed 2-3 upshift (25 - 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 260F
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
bailer towing in OD gear position (use "3" position if frequent shifting occurs)
Cooling system failure causing engine to operate over 230F
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.