2003 Pontiac Bonneville Owner's Manual - Page 264

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 the top left of the instrument panel. See Vehicle ldentification Number (VIN) on page5-90. This does not indicate a problem exists or that a higher-octane fuel is necessary. If you are using 87 octane or higher-octane fuel and you hear heavy knocking, your engine needs service. Gasoline Octane If your vehicle has the 3800 V6 engine (VIN Code K), 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 higer as soon as possible. Otherwise, you might damage your engine. A little pinging noise when you accelerate or drive uphill is considered normal. 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 a lower octane - as low as 87 - if heavy knocking does not occur. Refill your tank with premium fuel as soon as possible. Otherwise, you might damage your engine. If you are using 91 octane or higher-octane fuel and you hear heavy knocking, your engine needs service. 5-5