STATE EMISSIONS TESTING INFORMATION / PROCEDURE

SUBJECT: INFORMATION ON STATE EMISSIONS TESTING

MODELS: ALL 1982-91 TRUCKS

With more emphasis being placed on air quality, many states and municipalities have instituted vehicle inspection/ maintenance (I/M) programs, most of which include tail pipe exhaust emissions testing. GMC Truck desires to do its part both in helping achieve cleaner air and in making sure our customers' vehicles are tested in a satisfactory manner

A satisfactory exhaust emissions test includes making sure the vehicle's engine and emission control systems are fully warmed up just prior to conducting the test. An engine coolant temperature gauge that reads operating temperature or a warm radiator hose does not necessarily mean the vehicle is ready to be tested. For example, although the engine coolant temperature gauge may be reading at operating temperature, the catalytic converter may not be fully warmed up, which may cause exhaust emissions levels to be artificially high and not representative of whether the vehicle's emission control systems are functioning properly. Therefore, if the vehicle has been turned off or sitting at idle for several minutes, even though the engine coolant temperature gauge indi- cates the engine is at operating temperature, the vehicle should be driven on the road for a few minutes just prior to starting the official test to ensure that the engine and emission control systems are fully warmed up. An alternative warm up method that can be used and may be more conve- nient is running the engine at about 2500 rpm for two or three minutes with the transmission in park or neutral.

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.