For 1990-2009 cars

# BUZZING NOISE AT IDLE (INSTALL PRESSURE REGULATOR VALVE)

#### SUBJECT: BUZZING NOISE AT IDLE (INSTALL NEW PRESSURE REGULATOR VALVE)

#### MODELS AFFECTED: 1984-1993 FIREBIRD MODELS W/4L60 TRANSMISSION

TRANSMISSION APPLICATIONS: 1984-1993 HYDRA-MATIC 4L60 (MD8)

TRANSMISSION TYPE 4L60 700R4

TRANSMISSION MODELS: All

#### CONDITION:

--------- Some 1984-1993 vehicles equipped with a HYDRA-MATIC 4L60 transmission may have a buzzing noise coming from the transmission when the vehicle is at idle. The buzzing noise may be noticed more when the vehicle is in reverse at idle.

#### CAUSE:

----- The buzzing noise may be a result of pressure regulator valve oscillating due to oil pressure instability at lower idle RPM.

#### CORRECTION:

---------- A new pressure regulator valve (Ill. 218) has been made which will improve the oil pressure stability at lower RPM.

#### SERVICE PARTS INFORMATION:

Description Part Number ----------- ----------- Valve, Pressure Regulator (Ill. 218) 8684048 Parts are currently available from GMSPO.

#### WARRANTY INFORMATION:

Labor Operation No.: K6550 Labor Time : Use Applicable Labor Time.

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.