Transmission Control Systems: Description and Operation

TRANSMISSION CONTROL
The 42RLE 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 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. Some of these codes cause the Transmission to go into Limp-in mode. While in this mode, electrical power is taken away from the Transmission via the PCM, de-energizing the transmission control relay, and taking power from the solenoid pack. When this happens, the only Transmission mechanical functions are:
- Park and Neutral
- Reverse
- Second Gear

No upshifts or downshifts are possible. The position of the manual valve alone allows the three ranges that are available. Although vehicle performance is seriously degraded while in this mode, it allows the owner to drive the vehicle in for service.

Once the DRBIII(R) is in the Transmission portion of the diagnostic program, it constantly monitors the transmission 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.

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.

Once the DRBIII is in the "Transmission" 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(R) will flash the red LED.

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 42RLE 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 through a complex heat transfer equation using engine coolant temperature, battery/ambient temperature, and engine off time from the Body Control Module (BCM). These inputs are received from the PCI bus periodically and 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 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 26.6° C (-16° F)
- Goes to Cold schedule above -24° C (-12° F) oil temperature
- Park, Reverse, Neutral and 2nd gear only (prevents shifting which may fail a clutch with frequent shifts)

Cold: Oil temperature at start up above -24° C (-12° F) and below 2.2° C (36° F)
- Goes to Warm schedule above 4.4° C (40° F) oil temperature
- Delayed 2-3 upshift approximately 35-50 Km/h (22 - 31 MPH)
- Delayed 3-4 upshift 72-85 Km/h (45-53 MPH)
- Early 4-3 coastdown shift approximately 48 Km/h (30 MPH)
- Early 3-2 coastdown shift approximately 27 Km/h (17 MPH) ?
- High speed 4-2, 3-2, 2-1 kickdown shifts are prevented
- No EMCC

Warm: Oil temperature at start up above 2.2° C (36° F) and below 27° C (80° F)
- Goes to a Hot schedule above 27° C (80° F) oil temperature
- Normal operation (upshifts, kickdowns, and coastdowns)
- No EMCC

Hot: Oil temperature at start up above 27° C (80° F)
- Goes to a Overheat schedule above 115° C (240° F) oil temperature
- Normal operation (upshifts, kickdowns, and coastdowns)
- Full EMCC, No PEMCC except to engage FEMCC, except at closed throttle at speeds above 113-133 Km/h (70 - 83 MPH)

Overheat: Oil temperature above 115° C (240° F) or engine coolant temperature above 118° C (244° F)
- Goes to a Hot below 110° C (230° F) oil temperature or a Super Overheat above 115° C (240° F) oil temperature
- 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)

Super Overheat: Oil temperature above 127° C (260° F)
- Goes back to a Overheat below 115° C (240° F) oil temperature > All a Overheat shift schedules features apply
- 2nd gear PEMCC above 35 Km/h (22 MPH)
- Above 35 Km/h (22 MPH) the torque converter will not unlock unless the throttle is closed (i.e. at 80 Km/h (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 circuit.
- 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 (or A/S 3rd) 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 65° C (150° F), the transmission will disengage EMCC. Extended operation with the EMCC disengaged will cause the transmission to overheat.
- Brake switch issue 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
- Transmission Temperature Sensor circuit