1996 GMC Sonoma Owner's Manual - Page 225

Fuel Use regular unleaded gasoline rated at 87 octane or higher. At a minimum,. it should meet specifications ASTM D48 14 in the United States and CGSB 3.5-M93 in Canada. Improved gasoline specificationshave been developed by the American Automobile Manufacturers Association (AAMA) forbetter vehicle performance and engine protection. Gasolines meeting the AAMA specification could provide improved driveability and emission control system protection compared to other gasolines. Be sure the posted octane is at least 87. If the octane is less than 87, you may get a heavy knocking noise when you drive. If it's bad enough, it can damage your engine. If your vehicle is certified to meet California Emission Standards (indicated on the underhood tune-up label), it is designed to operate on fuels that meet California specifications. If such fuels are not available in states adopting California emissions standards, your vehicle will operate satisfactorily on fuels meeting federal specifications, but emission control system performance may be affected. The malfunction indicator lamp on your instrument panel may turn on and/or your vehicle may fail a smog-check test. If this occurs, return to your authorized GM dealer fordiagnosis to determine the cause of failure. In the event it is determined that the cause of the condition is the type of fuels used, repairs may not be covered by your warranty. In Canada, some gasolines contain an octane enhancing additive called MMT. If such fuels are used, your emission control system performance may be affected. The malfunction indicator lamp on your instrument panel may also turn on. If this occurs, return to your authorized GM dealer for service. If you're using fuel rated at 87 octane or higher and you still hear heavy knocking, your engine needs service. But don't worry if you hear a little pinging noise when you're accelerating or drivingup a hill. That's normal, and you don't have to buy a higher octane fuel to get rid of pinging. It's the heavy, constant knock that means you have a problem. 6-3