System Operation

GENERAL DESCRIPTION
This electronic transaxle is a conventional transaxle 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 transaxles.

FUNCTIONAL OPERATION
This electronic transaxle is a fully adaptive electronic control system. This 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 Transmission Control Module (TCM) continuously checks for electrical problems and some hydraulic problems. When a problem is sensed, the control module stores a diagnostic trouble code. All but 12 of these codes cause the transaxle to go into "limp-in" or "default" mode. While in this mode, electrical power is taken away from the transaxle via the TCM, de-energizing the transmission control relay, and taking power from the solenoid pack. When this happens, the only transaxle functions are:

- PARK and NEUTRAL
- REVERSE
- SECOND GEAR

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

Once the Diagnostic Readout Box (DRB) scan tool is in the 41TE portion of the diagnostic program, it constantly monitors the transmission control module to see if the system is in limp-in mode. If the transaxle is in limp-in, the DRB will flash the red LED.

Transaxle - Cut Away View:

Four speed transaxle, in which hydraulically applied clutches shift a planetary gear train.

Virtually all functions are electronically controlled, by a fully-adaptive [1] control system.

[1] The control system adapts transmission functions based on real-time information from feedback sensors, to ensure that clutch operation during upshifting and downshifting is more responsive without increased harshness.

GEAR RATIOS
- Forward ratios of 2.84, 1.57, 1.00, and 0.69 with torque converter clutch application available in 2nd, direct or overdrive gear;

- Reverse ratio is 2.21.

GEAR SELECTION
Conventional six position shift lever: P, R, N, OD, 3, and L.

SHIFTING AND TORQUE CONVERTER LOCK-UP
When OD is selected the transaxle shifts normally through all four speeds with torque converter clutch engagement in overdrive.

- This position is recommended for most driving.

The 3 position is tailored for use in hilly or mountainous driving.

- When 3 is selected, the transmission uses only 1st, 2nd, and direct gears with 2nd-direct shift delayed to 40 mph or greater.

- When operating in 3 or L positions torque converter clutch engagement occurs in direct gear for improved transmission cooling when towing trailers and on steep grades.

NOTE: If high engine coolant temperature occurs the torque converter clutch will also engage in 2nd gear.

The L position provides maximum engine braking for descending steep grades.

Unlike most transaxles. upshifts are provided to 2nd or direct gear at peak engine speeds, if the accelerator is depressed.

- This provides engine over-speed protection and maximum performance.

CONSTRUCTION
Four speed electronic 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 were designed with centrifugally balanced oil cavities.

- This allows quick response and good control at any speed.

A push/pull piston is incorporated for two of the three input clutches.

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

HYDRAULIC SYSTEM CONTROLS
- Manual Shift Lever Select Function
- Main Line Pressure Regulation
- Torque Converter Flow Control
- Cooler Flow Control

Flow to the friction elements is controlled directly by four solenoid valves.

TORQUE CONVERTER CLUTCH CONTROL VALVE
The hydraulics also include a unique logic-controlled "solenoid torque converter clutch control valve". This valve 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.

REGAINING ACCESS TO 1ST GEAR
To regain access to 1st gear, a special sequence of solenoid commands must be used to unlock and move the solenoid torque converter clutch control valve.

- This precludes any application of the first gear reaction element with other elements applied.

- It also allows one solenoid to control two friction elements.

HIGH-RATE ACCUMULATORS
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.