2004 Dodge Ram 3500 Pickup Owner's Manual - Page 258

258 STARTING AND OPERATING MMT In Gasoline MMT is a manganese-containing metallic additive that is blended into some gasoline to increase octane. Gasolines blended with MMT provide no performance advantage beyond gasolines of the same octane number without MMT. Gasolines blended with MMT reduce spark plug life and reduce emission system performance. We recommend that gasolines free of MMT be used in your vehicle. The MMT content of gasoline may not be indicated on the gasoline pump; therefore, you should ask your gasoline retailer whether or not his/her gasoline contains MMT. It is even more important to look for gasolines without MMT in Canada because MMT can be used at levels higher than allowed in the United States. MMT is prohibited in Federal and California reformulated gasolines. Sulfur In Gasoline If you live in the northeast United States, your vehicle may have been designed to meet California low emission standards with Cleaner-Burning California reformulated gasoline with low sulfur. If such fuels are not available in states adopting California emission standards, your vehicles will operate satisfactorily on fuels meeting federal specifications, but emission control system performance may be adversely affected. Gasoline sold outside of California is permitted to have higher sulfur levels which may affect the performance of the vehicle's catalytic converter. This may cause the Check Engine or Service Engine Soon light to illuminate. We recommend that you try a different brand of unleaded gasoline having lower sulfur to determine if the problem is fuel related prior to returning your vehicle to an authorized dealer for service.