INFO ON A/T (MP6/MP7) MID-YEAR PRODUCT CHANGES. Saturn Saturn 1992

For 1990-2009 cars

# INFO ON A/T (MP6/MP7) MID-YEAR PRODUCT CHANGES

#### SUBJECT: Information on Automatic Transaxle (MP6/MP7) Mid-Year Product Changes

#### MODELS AFFECTED:

SL1, SL2 Sedans and SC Coupes with automatic transaxles with VIN NZ200001 through NZ200100, and all vehicles built from, and including NZ205625.

#### PURPOSE:

The purpose of this bulletin is to provide technical information on the changes to both the MP6 and MP7 automatic transaxles. These changes will occur, April, 1992, and affect all vehicles with VIN ranges given above under "Models Affected." All references to 2nd design, denote changes to be made to transaxle after April, 1992. References to 1st design, denote transaxle prior to changes being made in April, 1992.

#### IMPORTANT: The parts listed in this bulletin are not interchangeable between 1st and 2nd design.

REASON FOR CHANGE

The main reason for changing the automatic transaxle is to prohibit the dog clutch from being activated when the vehicle is moving forward. This is accomplished by controlling oil flow to the forward/reverse servo piston which operates the dog clutch, selecting either 2nd or reverse gear. The oil is controlled to the piston by the addition of a servo apply valve which is described below and illustrated in Figure 6.

PARTS AFFECTED AND HOW TO IDENTIFY DIFFERENCES

Automatic Transaxle Control Body Assembly (Valvebody) The automatic transaxle control body assembly (called the valvebody in this bulletin) has been completely redesigned. Major changes include the elimination of the TCC enable valve, actuator feed mode valve, and the line boost plunger. The spacer plate and gaskets have also been redesigned along with the manual valve. A servo apply valve has been added (operation described below). Refer to Figures 2 through 5 for exploded views of both types of valvebodies. Figure 5 will indicate the location of an identification mark for the 2nd design valvebody.

Torque Converter Clutch (TCC) Enable Valve The torque converter clutch (TCC) enable valve has been eliminated in the new design. This valve was used primarily to disable TCC when in P, N, manual D2 and 1st gear. By disabling the TCC in these quadrants, the vehicle can still be driven forward with a TCC stuck ON condition. Logic has been added to the PCM (powertrain control module) to detect a TCC stuck ON condition, so the TCC valve is no longer required. Elimination of the valve simplifies the valvebody.

Actuator Feed Mode Valve The actuator feed mode valve has also been eliminated to simplify the system. The elimination of this valve will only have an affect when certain conditions are detected by the PCM. On transaxles built before this change, if a certain condition exists, the PCM will detect the condition and illuminate the "SHIFT TO D2" lamp. When the driver selects manual D2, the system will go to boost pressure and allow a 2nd gear start. When selecting D2 on the new system, the vehicle may start out in any forward gear depending on the failure condition. Elimination of this valve simplifies the valvebody.

Line Boost Plunger The line boost plunger, located in the pressure regulator valve, has also been eliminated. Line pressure is now totally controlled by the PCM, line actuator and the line pressure regulator.

THEORY OF OPERATION OF NEW COMPONENTS

Servo Apply Valve The servo apply valve, located in the valvebody is used to control reverse apply oil to the forward/reverse servo piston. When reverse is selected, the manual valve will allow oil to be applied to the servo apply valve. If vehicle speed input to the PCM indicates the vehicle is less than 8 km/h (5 mph), then the dog clutch can be moved to the reverse direction without causing damage. With vehicle speed less than 8 km/h (5 mph), and reverse selected, the PCM will command high-line pressure. When high-line pressure is commanded, the pressure will move the servo apply valve against the spring which opens up the passage allowing oil to pass through the servo apply valve to the forward/reverse servo piston.

Refer to Figure 6 showing hydraulic schematic while in Reverse. If reverse is selected when vehicle speed is greater then 8 km/h (5 mph), the PCM will command low-line pressure causing the servo apply spring to keep the passage in the servo apply valve closed, preventing oil to reach the forward/reverse servo piston. This action does not allow the dog clutch to move, thus preventing internal damage to the transaxle.

Spacer Plate and Spacer Plate Gasket The spacer plate and spacer plate gaskets are redesigned to accommodate the new valvebody. The 1992 2nd design parts will contain an identification mark as shown in Figure 7.

Forward/Reverse Servo Piston And Spring In addition to the servo valve previously described, the forward/reverse servo piston and spring have been redesigned. The main difference in the new piston is that the step and a hole in the shaft have been eliminated. Also, the spring in the new design is longer. Figures 8 and 9 show the differences.

Transaxle Case Assembly Due to the elimination of the step in the forward/reverse servo piston, the case has been redesigned to accommodate the removal of this step.

#### IMPORTANT: The new case can be identified by a "SV," located on the casting below the case-to-cradle mount holes.

Manual Valve Due to valvebody changes, the manual valve has also been redesigned for directing oil to the proper hydraulic circuits. The new manual valve is illustrated in Figure 10. The new valve will have a slot instead of a flat near the end which connects the valve to the linkage.

#### IMPORTANT: When installing the 2nd designed manual valve, the notch must be facing up.

Powertrain Control Module In addition to changes in the transaxle, there are changes in the PCM which make a new PCM a requirement. The new PCM cannot be used on previous models. The logic for preventing dog clutch engagement when the vehicle speed is present has been added, and the most noticeable change is that under certain drive/idle conditions, low-line pressure or high pressure line will be commanded. This change will eliminate the actuator buzzing noise detected while at idle and when the transaxle is in drive.

DIAGNOSIS

New diagnostic charts, included in this bulletin, are required when diagnosing a problem with a 2nd designed transaxle.

o Pressure test (Figure 11)

o No Reverse trouble tree chart

o No TCC, Code 25 trouble tree chart

PARTS LIST AND PART NUMBER CHANGES

1991 and 1992 1992 Part 1st Design 2nd Design ---- ------------- ---------- Control Body Asm- A/Trans 21002273 21002691 Valve-Manual 21001539 21002695 Piston-FWD-REV Servo 21002552 21002547 Spring-FWD-REV Servo 21002553 21002626 Case-A/Trans 21002449 21002622 Gasket-Spacer Plate 21002527 21002390 Plate-Spacer 21002410 21002389 Module Asm-Powertrain Control Base Auto (LKO) 21021221 (91) 21022078 21021469 (92) PERF Auto (LLO) 21021220 (91) 21022079 21021470 (92)

#### NOTICE: The parts listed in this bulletin are not interchangeable between 1st and 2nd design.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.