[Manitcor]

Subject:Incorrect Transmission Shifts, Poor Performance of Engine, Transmission Slipping, SES Lamp Illuminated, DTC P0756, P0757 (Clean Transaxle Valve Body and Case Oil Passages of Debris)



Models: 2001-2002 Buick Century, LeSabre, Park Avenue, Regal
2002 Buick Rendezvous
2001 Chevrolet Lumina
2001-2002 Chevrolet Impala, Monte Carlo, Venture
2001-2002 Oldsmobile Aurora, Intrigue, Silhouette
2001-2002 Pontiac Aztek, Bonneville, Grand Prix, Montana
with 4T65E Transmission (RPOs M15, MN3, MN7, M76)



Condition:
Some owners may comment on any one or more of the following conditions:

The SES lamp is illuminated.
The transmission slips.
The transmission does not shift correctly, is very difficult to get the vehicle to start moving or the engine lacks the power to move the vehicle.



Cause:
The most likely cause of the various conditions may be chips or debris:

Plugging an orifice on the case side of the spacer plate.
Restricting the movement of the 2-3 shift valves in the valve body.
Restricting the movement of the 3-4 shift valves in the valve body.
Technician Diagnosis
The vehicle will usually have less than 4800 km (3000 mi).
The technician's road test reveals the vehicle launches in third or fourth gear (high RPM with slow vehicle acceleration).
DTC P0756 or P0757 may be found with the Tech 2.
With the Tech 2 connected to the vehicle, a road test must be performed:
If vehicle performance is normal, skip to Step 4 of the Correction section. If a problem exists with the vehicle, proceed with the next step.
Command third gear with the Tech 2. If the displayed gear ratio is something other than 1:1, go to Step 1 of the Correction section.
Command fourth gear with the Tech 2. If the displayed gear ratio is something other than 0.7:1, go to Step 2 of the Correction section.



Correction:
Remove the valve body. Carefully disassemble and clean the complete valve body. Pay particular attention to the 2-3 shift valve. Inspect the bore for machining chips and carefully clean as necessary. Reinstall the 2-3 shift valve components and verify the valve is moving freely. Go to Step 3.
Remove the valve body. Carefully disassemble and clean the complete valve body. Pay particular attention to the 3-4 shift valve. Inspect the bore for machining chips and carefully clean as necessary. Reinstall the 3-4 shift valve components and verify the valve is moving freely. Go to Step 3.
Clean the channels of the transaxle case assembly thoroughly. Inspect the case channels for debris. When satisfied the case channels are thoroughly cleaned of all debris, reinstall the valve body using new spacer plate gaskets or the newly released bonded spacer plate and gasket assembly.


If the technician is unable to reproduce the condition after an extensive road test, the chip which caused the concern has likely been exhausted from the affected valve or spacer plate. No further action on the part of the technician is necessary.



GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these 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 your GM dealer for information on whether your vehicle may benefit from the information.


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