TRANSAXLE REMAINS IN 3RD GEAR WHEN 3-2 DOWNSHIFT IS DESIRED

SUBJECT: TRANSAXLE REMAINS IN THIRD GEAR WHEN 3-2 DOWNSHIFT IS DESIRED (CODE P029) OR REMAINS IN SECOND GEAR

MODELS AFFECTED: 1993 ELDORADOS, SEVILLES, AND ALLANTES WITH HYDRA-MATIC 4T80-E (RPO MHl)

Some 1993 Eldorados, Sevilles, and Allantes equipped with the Hydra-Matic 4T80-E (RPO MH1) transaxle built on or before Julian Date 318 (November 14, 1992) may remain in third gear when a 3 - 2 downshift is desired or remain in second gear when a 2 - 3 upshift is desired. A code P029 may be set by the PCM due to the no 3 - 2 downshift condition.

This condition may be caused by the 2-3 valve train (907, 908) in the lower control valve assembly (903) which has a valve interlock feature. Some valves may have been manufactured with the interlock misaligned causing the 3 - 2 valve train to bind in the valve body bore. To diagnosis this condition perform the following procedure:

Road Test

NOTE: Road test should only be performed when traffic and road conditions permit. Observe all traffic safety regulations.

1. Start vehicle.

2. Enter diagnostics and select PCM parameter PD76 "transaxle gear ratio". Shift solenoid "A'is the "OFF light for Eldorados, Sevilles, and Allantes; and shift solenoid "B" is the "ECON" light for Allantes and "DEFOG" (word not symbol) for Eldorados and Sevilles. When the solenoids are energized, the indicators light up and turn off when the solenoids are de-energized.

3. Move gear selector into D4 (overdrive range) and accelerate to 40 mph (accelerate under light throttle (DO NOT SNAP THROTTLE OPEN). Verify vehicle is in fourth gear by checking solenoid state on Electronic Climate Control display. (Solenoid "a" energized, solenoid "B" energized.)

4. Remove foot from accelerator pedal completely (zero throttle).

5. Now depress accelerator pedal (with medium speed) to approximately 30 percent of accelerator pedal travel (DO NOT SNAP IT OPEN). During the same motion accelerate (with fast speed) to Wide Open Throttle (WOT) to force a 3 - 2 downshift. Throttle movement from zero throttle to WOT must be a continuous movement.

6. Observe solenoid state. When the 3-2 shift is completed, both the "OFF" and "ECON" or "DEFOG" lights on the Electronic Climate Control display should be off and PD76 should show 1.63. If the 2-3 valve sticks, the "OFF" and "ECON" or "DEFOG" lights will still go out (light off) but the ratio will be 1.00. This indicates the PCM commanded the transaxle into second gear but stayed in third gear due to a stuck 2-3 shift valve.

If the above procedure indicates that the 2-3 shift valve is sticking, the channel plate/control valve and housing assembly (903) must be replaced.

NOTE: The terms of limited on-vehicle service as outlined in DSIB 92-I-45 under "General Guidelines" will be temporarily lifted for this condition. All other concerns related to the 4T80-E transaxle must be treated as in the past.

To replace the channel plate/control valve and housing assembly (903) perform the following procedure:

1. Raise vehicle and support.

2. Place drain pan under transaxle bottom pan to catch fluid. Loosen the 16 bottom pan bolts (62) and remove bottom pan (59) and bottom pan seal (61). Refer to Figure 1. Allow transaxle to drain completely.

3. Remove left and right scavenger screens (51, 52) and seals (53) and discard. Use caution when removing seals not to score or damage the case.

4. Disconnect "A" and "B" shift solenoids and transaxle pressure switch connectors. Refer to Figure 2.

5. Disconnect manual valve linkage clip (915). Refer to Figure 2.

6. Remove nine oil transfer plate bolts (534) and oil transfer plate (956). Refer to Figure 3.

7. Remove ten lower channel plate bolts (534), two nuts (955), lower channel plate control valve, and accumulator assembly (lower controls assembly) from transaxle. (DO NOT REMOVE indicated bolts in lower channel plate.) Refer to Figure 3.

8. Center the low reverse band and position using a 12" length of .020" shim stock. A mispositioned low reverse band during assembly will result in a no first gear/no engine braking/no reverse condition. Refer to Figure 4.

9. For transaxle models 2AJH, 3AJN, and 3ARN install lower controls assembly, P/N 8682762. For transaxle model 3AAN install lower controls assembly, P/N 8684463. Hold the new lower controls assembly to transaxle using the forward support studs to locate.

10. Hand start ten bolts and two nuts in channel plate. Bolts without flanges are located next to oil transfer plate. Torque bolts and nuts to 12 Nm (106 lbs. in.). Remove shim stock. Refer to Figure 5.

11. Install oil transfer plate and hand start nine bolts. Torque to 12 Nm (106 lbs. in.). Refer to Figure 3.

12. Connect manual valve (915) to detent lever (17). Refer to Figure 2.

13. Route wiring harness under spacer plate rib and detent lever. Connect wiring harness to "A" and "B" shift solenoids (909) and transaxle pressure switch (936). Refer to Figure 2.

14. Install left and right scavenger screen seals, and screens (51, 52, and 53). Refer to Figure 1. 15.

15. Remove any residual transaxle fluid from gasket sealing surface of the case, the outside surface of the case, case bolts, bottom pan, and bolt holes. Use a rubber tipped air hose on the case bolt holes to remove fluid if necessary. All of the bottom pan bolts MUST be completely dry before installation.

IMPORTANT- Failure to remove oil from oil pan, case surface, and case bolt holes, will greatly reduce the efficiency of the gasket and may cause a leak in the future.

16. Position the new gasket and bottom pan on the transaxle.

IMPORTANT- Bottom pan seal is not reusable. Install new bottom pan gasket and scavenger screen and bolt package, P/N 8684953.

17. Hand start all of the bottom pan bolts. (Follow the torque sequence listed in Figure 6.) Torque all bolts to 3 Nm (27 lbs. in.) in the sequence shown in Figure 6, then to 6 Nm (53 lbs. in.), then finally to 12 Nm (106 lbs. in.).

IMPORTANT- The final torque specification of 12 Nm (106 lbs. in.) must not be exceeded. If this specification is exceeded, the bottom pan gasket and case could be damaged and a transaxle fluid leak may result.

18. Add four quarts of transmission fluid and top off fluid levels as necessary per the following fluid level checking procedure.

Fluid Level Checking Procedure:

To accurately check fluid level of the Hydra-Matic 4T80-E transaxle, the unit must be at normal operating temperature (180-200 degrees F, 82-93 degrees C - parameter PD77 gives the transaxle temperature in Celsius).

1. Park vehicle on a level surface with transaxle at normal operating temperature.

2. With foot on brake, move shift level through each range pausing for about three seconds in each range ending in park.

3. Apply parking brake.

4. Let engine idle for three minutes.

5. Remove transaxle fluid level indicator, wipe clean, and reinsert fully twisting closed.

6. Wait three seconds and remove indicator.

7. Read both sides of indicator and use lowest level. Fluid level must be within the "hot" cross-hatched area.

NOTE: If the brake pedal is applied during this procedure, it may affect the fluid level reading.

Parts are expected to be available on February 8, 1993.

4T80-E BOTTOM PAN GASKET INSTALLATION PROCEDURE

1. Remove bottom pan gasket and discard.

2. Remove any residual transmission fluid from the gasket surface of the case, the bottom pan, and the screws (16). All of the screws must be completely dry upon re-installation.

3. The bottom pan screw threads in the case must be completely free of transmission fluid. Use a rubber tipped air hose to dry if necessary. Wipe any residual fluid from the outside of the case.

4. Install the new gasket and then the bottom pan and screws. The screws must be hand started and then tightened following the sequence pattern illustrated below.

5. Following the sequence pattern, Torque all screws first to 3 N.m., then all screws to 6 N-m., and finally all screws to 10-1 2 N.m.

IMPORTANT: The final torque specification of 10-12 N.m. must not be exceeded. If this specification is exceeded, the bottom pan gasket could be damaged and a transaxle fluid leak may result.

WARRANTY INFORMATION VEHICLE SERIES Operation Operation Description Number C D E I K v

Valve Assembly, Lower Control-Replace K6610 1.2 1.2 1.2

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.