Transmission Control

TRANSMISSION CONTROL
The 45RFE/545RFE 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 (DTC). Some of these codes cause the transmission to go into "limp-in" or "default" mode. The 45RFE/545RFE has three default modes:

(I) Immediate shutdown - The PCM de-energizes the transmission control relay. This causes the transmission system to immediately default to third gear if the 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 PCM recognizes a problem that does 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 PCM 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 PCM 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 is in the "EATX" 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 will flash the red LED.