For 1990-2009 cars

# SHUDDER/VIBRATION AT LOW SPEED (INSTALL NEW PROM)

#### SUBJECT: SHUDDER OR VIBRATION AT LOW SPEEDS (INSTALL NEW PROM)

#### VEHICLES AFFECTED: 1990-1991 U-VAN WITH 3.1L

#### Condition:

----------- Some owners of 1990 - 1991 U-vans with 3.lL (VIN D) engine may comment of a Shudder or Vibration at Low Speeds.

#### Cause:

------- This condition may be caused by the transmission converter clutch being engaged at 23 MPH.

#### Correction:

------------ If normal diagnostic procedures shown in your Service Manual (Section 6E2-B-3) do not correct this condition, a new PROM with a "TCC" (torque converter clutch) engagement speed of 35 MPH is available. The part numbers are as follows:

#### 1990 Vehicles

Emission PROM Scanner Broadcast System Package No. I. D. Code --------- ------------ ------- --------- Federal 16163426 3441 AYAD

1991 Vehicles

Federal 16164893 4901 AYHN

#### Note: This correction will have ho impact on performance above 56 KPH.

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.