Transmission Controls Description

CLUTCH AND GEAR
The 42LE transaxle consists of:
- Three multiple-disc input clutches
- Two multiple-disc grounded clutches
- Four hydraulic accumulators
- Two planetary gear sets

This provides four forward ratios and a reverse ratio. The clutch apply pistons have centrifugally balanced oil cavities so that quick response and good control can be achieved. A push/pull piston is incorporated for two of the three input clutches.

CAUTION: Some clutch packs appear similar, but they are not the same. Do not interchange clutch components as they might fail.

HYDRAULICS
The hydraulics of the transaxle provide:
- Manual shift lever select function
- Main line pressure regulation
- Torque converter flow control
- Transaxle oil cooler flow control

Oil flow to the friction elements is controlled directly by four solenoid valves. The hydraulics also include a logic-controlled solenoid switch valve. It locks out the 1st gear reaction element with the application of 2nd, direct, or overdrive gear elements. It also redirects the 1st gear solenoid output so that it can control torque converter clutch operation. To regain access to 1st gear, a special sequence of solenoid commands must be used to unlock and move the solenoid switch valve. This precludes any application of the 1st gear reaction element with other elements applied. It also allows one solenoid to control two friction elements.

Small, high-rate accumulators are provided in each controlled friction element circuit. These serve to absorb the pressure responses, and allow the controls to read and respond to changes that are occurring.

SOLENOIDS
Since the solenoid valves perform all control functions, these valves must be durable and tolerant of dirt particles. For that reason hardened-steel poppet and ball valves are used. These are free from any close operating clearances, and the solenoids operate the valves directly. Direct operation means that these units must have very high output. They must close against the sizeable flow areas and high line pressures. Fast response is also required to meet the control requirements.

Two of the solenoids are normally-venting and two are normally-applying; this was done to provide a default mode of operation. With no electrical power the transmission provides 2nd gear in OD, 3, or L shift lever positions. All other shift lever positions will function normally. The choice of 2nd gear was made to provide adequate performance while still accommodating highway speeds.

SENSORS
There are three pressure switches which identify solenoid application. The pressure switches are incorporated in an assembly with the solenoids. Two speed sensors read input (torque converter turbine) and output (parking sprag) speeds. There is also a Transmission Range Sensor (TRS) which senses manual valve position.

Engine speed, throttle position, temperature, etc., are also observed. Some of these signals are read directly from the engine control sensors, others are read from a multiplex circuit with the engine controller.

ADAPTIVE CONTROLS
These controls function by reading the input and output speeds over 140 times a second and responding to each new reading. This provides the friction element control needed to make smooth clutch-to-clutch shifts for all gear changes without the use of overrunning clutches. As with most automatic transaxles, all shifts involve releasing one element and applying a different element. In simplified terms, the upshift logic allow-e the releasing element to slip backwards slightly to ensure that it does not have excess capacity; the apply element is filled until it begins to make the speed change to the higher gear; its apply pressure is then controlled to maintain the desired rate of speed change until the shift is complete. The key to providing excellent shift quality is precision; for example, as mentioned, the release element for upshifts is allowed to slip backwards slightly; the amount of that slip is typically less than a total of 20 degrees. To achieve that precision, the transmission control module learns the characteristics of the particular transaxle that it is controlling. It learns:
- The release rate of the releasing element.
- The apply time of the applying element.
- The rate the apply element builds pressure.

This method achieves more precision than would be possible with exacting tolerances. It can also adapt to any changes that occur with age or environment.

For kickdown shifts, the control logic allows the releasing element to slip. Then controls the rate at which the input (and engine) accelerate. When the lower gear speed is achieved, the releasing element reapplies to maintain that speed until the apply element is filled. This provides quick response and a smooth torque exchange since the release element can control the rate of torque increase. This control can make any powertrain feel more responsive without increasing harshness.

Adaptive controls respond to input speed changes. They compensate for changes in engine or friction element torque. Thus providing consistent shift quality for the life of the transaxle.

ON-BOARD DIAGNOSTICS
These controls also provide comprehensive, on-board transaxle diagnostics. The information available can aid in transaxle diagnosis. For example, apply element buildup rate indicates solenoid performance. Also included are self-diagnostic functions which allow the technician to test the electronic controls. The transmission control module monitors its critical functions, records any malfunctions, and the number of engine starts since the last malfunction. The technician can use this information in the event of a customer complaint.

TRANSMISSION CONTROL MODULE
The transmission control module is located in the trunk compartment on the right side of the vehicle. It is held in place by four mounting screws.

NOTE: If the transmission control module has been replaced, refer to Quick Learn Procedure. This program will allow the transmission control module to learn the characteristics of the vehicle.

TRANSMISSION CONTROL RELAY
The transmission control module controls power to the solenoid pack through the transmission control relay. The relay is located in the power distribution center in the engine compartment, on the lower left side of the engine.

SOLENOIDS
Since the solenoid valves perform all control functions, these valves must be durable and tolerant of dirt particles. For that reason hardened- steel poppet and ball valves are used. These are free from any close operating clearances, and the solenoids operate the valves directly. Direct operation means that these units must have very high output. They must close against the sizeable flow areas and high line pressures. Fast response is also required to meet the control requirements.

Two of the solenoids are normally-venting and two are normally-applying; this was done to provide a default mode of operation. With no electrical power, the transmission provides 2nd gear in OD, 3, or L shift lever positions. All other shift lever positions will function normally. The choice of 2nd gear was made to provide adequate performance while still accommodating highway speeds.

SHIFTER/IGNITION INTERLOCK
The ignition interlock system connects the automatic transmission shifter and the lock system. With the ignition key in the OFF or ACCESSORY position, the interlock system holds the transmission shifter in park. When the key is in the UNLOCK or RUN position the shifter unlocks and can be moved to any position. Also, if the shifter is not in PARK, the system prevents the operator from turning the ignition switch to the OFF or ACCESSORY positions.

NOTE: Adjust the interlock cable after replacing the lock cylinder. Refer to Shifter/Ignition Interlock Adjustment.

TRANSMISSION RANGE SENSOR
The Transmission Range Sensor (TRS) interprets the position of the manual valve. This information is sent to the transmission control module. Also the TRS provides for Park/Neutral only starter operation and back-up lamp operation.

The TRS connector extends outside the transaxle on the left side, next to the fill tube. The TRS is mounted to the top of the valve body. The TRS and valve body must be removed from the transaxle as an assembly.

AUTOSTICK
Autostick is a driver-interactive transaxle feature that offers manual gear shifting capability. When the shifter is moved into the Autostick position, the transaxle remains in whatever gear it was using before Autostick was activated. Moving the shifter to the left (towards the driver) causes a downshift and moving to the right (towards the passenger) causes an upshift. The instrument cluster will illuminate the selected gear. The vehicle can be launched in 1st 2nd, or 3rd gear while in the Autostick mode. The speed control is operable in 3rd and 4th gear Autostick mode. Speed control will be deactivated if the transaxle is shifted to 2nd gear. Shifting into OD position cancels the Autostick mode, and the transaxle resumes the OD shift schedule.

SHIFT POSITION INDICATOR
The shifter position indicator is located in the instrument cluster. The shifter position indicator outlines with a box the gear position the transaxle manual valve lever is in.

The Transmission Range Sensor (located on the valve-body) sends a signal to the Transmission Control Module (TCM) on the position of the transaxle manual valve lever. The TCM receives the switch signal and processes the data. The TCM sends the Shift Lever Position (SLP) information to the Body Control Module (BCM) via the CCD bus. The BCM then outlines the appropriate shifter position indicator in the instrument cluster.