CTS 2003-2005

Fuel & Oil Recommendations



Some fuel additives contain chemicals that can damage the catalytic converter and/or the oxygen sensors. Read all of the labels carefully before using any additive in the engine or fuel system.

All of the vehicles covered herein are designed to run on unleaded fuel. The use of a leaded fuel in a vehicle requiring unleaded will plug the catalytic converter and render it inoperative. It will also increase exhaust backpressure because the material in the converter will tend to collapse and plug the exhaust, severely reducing engine power. The minimum octane rating of the unleaded fuel being used must be at least 87, which usually means regular unleaded, but some high performance engines may require higher octane ratings. Fuel should be selected for the brand and octane which performs best with your engine.

All of the engines covered herein require a fuel with an octane rating of 87 or higher, except for the 3.8L (VIN 1) supercharged engine which requires premium fuel with an octane rating of 92 or higher.

The use of a fuel too low in octane (a measure of anti-knock quality) will result in spark knock. While the computer controlled ignition system uses knock sensors to detect knock and then electronically adjust the ignition timing to compensate, there is a limit to the system's adjustment capability. Since many factors such as altitude, terrain, air temperature and humidity affect operating efficiency, some light knocking (usually on acceleration) may result and is even considered normal. But if persistent knocking occurs, it may be necessary to switch to a higher grade of fuel. Continuous or heavy knocking may result in engine damage.