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/545RFE transmission. The Temperature Sensor is an integral component of the Transmission Range Sensor (TRS). If the Temperature Sensor is faulty, (DTC P-1799) 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 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. The key highlights of the various shift schedules are as follows:

Extreme Cold:
- Oil temperature below -27 °C (-16 °F)
- Goes to "Super Cold" schedule when temp rises above -24C (-12 °F) oil temperature
- Park, Reverse, Neutral and 1st and 3rd gear only
- No Torque Converter Clutch engagement

Super Cold:
- Oil temperature between -27 °C (-16 °F) and -17 °C (0 °F)
- Goes to "Cold" schedule above -12 °C (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 -17 °C (0 °F) and 2 °C (36 °F)
- Goes to "Warm" schedule when temp rises above 4.4 °C (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
- Torque Converter Clutch engagement allowed with sump temp greater than 18 °C (65 °F)

Warm:
- Oil temperature between 2 °C (36 °F) and 27 °C (80 °F)
- Normal operation (upshifts, kickdowns, and coastdowns)
- No Torque Converter Clutch engagement allowed until sump temp above 18 °C (65 °F)

Hot (Normal operation):
- Oil temperature between 27 °C (80 °F) and 115 °C (240 °F)
- Goes to "Overheat" schedule above 115 °C (240 °F) oil temperature
- Reverts to "Hot" when temp falls below 110 °C (230 °F)
- Normal operation (upshifts, kickdowns, and coastdowns)
- Normal Torque Converter Clutch engagement operation

Overheat:
- Oil temperature above 115 °C (240 °F) or engine coolant temperature above 118 °C (244 °F)
- Reverts to "Hot" when temp falls below 110 °C (230 °F) oil temp
- Delayed 2-3 upshift 40-51 km/h (25-32 mph)
- Delayed 3-4 upshift 66-77 km/h (41-48 mph)
- 3rd gear FEMCC from 48-77 km/h (30-48 mph)
- 3rd gear PEMCC from 43-50 km/h (27-31 mph)
- A DTC P0218 High Temperature Operation Activated will be set in the TCM.

Causes for operation in the wrong temperature shift schedule:

Extreme Cold or Cold shift schedule at start up:
Temperature Sensor or circuitry.

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
Long idle time in drive position
Trailer towing in OD gear position (use "3" position if frequent shifting occurs)
Cooling system failure causing engine to operate over 110 °C (230 °F)

Engine coolant temperature stays low too long - If engine coolant temperature drops below 66 °C (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 problem with the 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.