2003 GMC Sonoma Owner's Manual - Page 268

Fuel The 8th digit of your vehicle identification number (VIN) shows the code letter or number that identifies your engine. YOU will find the VIN at ihe top iefi of the instrument panel. See Vehicle Identification Number (VIN) on page 5-94. Gasoline Specifications It is recommended that gasoline meet specifications which were developed by the American Automobile Manirfacttirers Association and endorsed by the Canadian Vehicle Manufacturers Association for better vehicle performance and engine protection. Gasoline meeting these specifications could provide improved driveability and emission control system performance compared to other gasoline. In Canada, look for the "Auto Makers' Choice" label on the pump. Gasoline Octane Use regular unleaded gasoline with a posted octane of 87 or higher. If the octane is less than 87, you may get a heavy knocking noise when you drive. If this occurs, use a gasoline rated at 87 octane or higher as soon as possible. Otherwise, you might damage your engine. A little pinging noise when you accelerate or drive uphill is considered normal. This does not indicate a problem exists or that a higher-octane fuel is necessary. If you areusing 87 octane or higher-octane fuel and hear heavy knocking, your engine needs service. w r Canada Only 5-5