Trans Operation and Shift Scheduling at Various Oil Temps

The transaxle 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 thermistor on the 41 TE/AE transmission. The thermistor is an integral component of the Transmission Range Sensor (TRS). If the thermistor is faulty, (P1799) the transmission will default to a "calculated" oil temperature. Oil temperature will then be calculated through a complex heat transfer equation which uses engine coolant temperature, battery/ambient temperature, and engine off time from the Body Control Module (BCM). These inputs are received from the CCD bus periodically and 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 with "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 at start up below -16°F
^ Goes to "Cold" schedule above -12° oil temperature
^ Park, Reverse, Neutral and 2nd gear only (prevents shifting which may fail a clutch with frequent shifts)
^ No EMCC

Cold: Oil temperature at start up above -12°F and below 36°F
^ Goes to "Warm" schedule above 40° oil temperature
^ Delayed 2-3 upshift. (approximately 22 - 31 MPH)
^ Delayed 3-4 upshift (45-53 MPH)
^ Early 4-3 coastdown shift (approximately 30 MPH)
^ Early 3-2 coastdown shift (approximately 17MPH)
^ High speed 4-2, 3-2, 2-1 kickdown shifts are prevented
^ No EMCC

Warm: Oil temperature at start up above 36°F and below 80°F
^ Goes to "Hot" schedule above 80° oil temperature
^ Normal operation (upshifts, kickdowns, and coastdowns)
^ No EMCC

Hot: Oil temperature at start up above 80°
^ Goes to "Overheat" schedule above 240° oil temperature
^ Normal operation (upshifts, kickdowns, and coastdowns)
^ Full EMCC, No PEMCC except to engage FEMCC (Except at closed throttle at speeds above 70-83 MPH)

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 (25-32 MPH)
^ High speed 4-3 coast down at 40-47 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°
^ 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 is closed (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:
^ Defective thermistor circuit.
^ Defective engine coolant temperature sensor
^ Defective battery/ambient temperature sensor
^ Defective PCM/TCM.
Overheat or Super Overheat shift schedule after extended operation:
^ Operation in city traffic or stop and go traffic
^ Engine idle speed too high
^ 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°, the transmission will disengage EMCC. Extended operation with the EMCC disengaged will cause the transmission to overheat.
^ A defective brake switch 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
^ Cooling fan inoperative
^ Defective thermistor circuit
^ Defective PCM/TCM