2003 Pontiac Grand Prix Owner's Manual - Page 230

Gasoline Specifications 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 the top left of the instrument panel. See Vehicle Identification Number (VIN) on page 5-96. It is recommended that gasoline meet specifications which were developed by the American Automobile Manufacturers 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 If yourvehicle has the 3100 V6 engine (VIN Code J) or 3800 V6 engine (VIN Code K), use regular unleaded gasoline with aposted octane of 87 or higher. If the octane is less than 87, you may get a heavy knocking noise when you drive. it is badenough, it can damage If 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 your vehicle has the 3800 Supercharged V6 engine (VIN Code I ) , use only premium unleaded gasoline with a posted octane of 91 or higher.In an emergency, you may be able to use alower octane - as low a 87 if heavy knocking does not occur. Refill your tank with premium fuel as soon as possible. If you are using 91 octane or higher-octanefuel and you hear knocking, your engine needs service. Canada Only 5-5