For 1990-2009 cars

# BUZZING NOISE AT IDLE (INSTALL PRESSURE REGULATOR VALVE)

#### SUBJECT: BUZZING/CHIRP NOISE ON ENGINE SHUTDOWN OR BUZZ NOISE AT IDLE - INSTALL NEW PRESSURE REGULATOR VALVE

#### MODELS/YEARS: 1991-92 CUSTOM CRUISER AND 1991-93 BRAVADA W/4L60 OR 4L60-E TRANSMISSION

CONDITION: Some 1991-92 Bravadas and Custom Cruisers (4L60) may exhibit a buzzing noise from the transmission at idle. This noise may be noticed more at idle in reverse. Also, some 1993 Bravadas (4L60-E) may exhibit a buzz/chirp noise from the transmission at engine shutdown.

CAUSE: The buzzing noise may be a result of the pressure regulator valve oscillating due to oil pressure instability during engine shutdown.

CORRECTION: A new pressure regulator valve has been released which will improve the oil pressure stability at lower RPM. Parts are currently available from GMSPO. This repair can be performed on a 1993 4L60-E prior to January 1, 1993 even though the pressure regulator valve is not included in the list of service parts available in Dealer Technical Bulletin 93-T-07.

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.