System Description and Functional Operation

GENERAL DESCRIPTION
The 42LE electronic Transmission is a conventional Transmission in that it uses hydraulically applied clutches to shift a planetary gear train. However, the electronic control system replaces many of the mechanical and hydraulic components used in conventional transmission valve bodies.

FUNCTIONAL OPERATION
The 42LE electronic Transmission has a fully adaptive control system. The system performs it's 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 or default 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 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.