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This paper presents the results of a three city survey designed to determine the relative frequency of illumination of vehicle on-board diagnostic (OBD) malfunction indicator lights (MIL) on 2001 and later model year vehicles. The survey was conducted in a Canadian market, Regina, and two U.S. markets, Minneapolis and Denver, to assess claims that the presence of methycyclopentadienyl manganese tricarbonyl (MMT®) in gasoline causes the failure of technology necessary to meet stringent Tier 2 emission standards applicable in North America. The results of the survey do not support the claim that MMT® is incompatible with the effective functioning of the advanced vehicle emission technology necessary to meet Tier 2 emission standards. The results substantiate that the performance of the most advanced vehicles operating on gasoline containing MMT® is not materially different from the performance of comparable vehicles operating on gasoline that does not contain MMT®.

The Clean Air Act of 1990 requires on-board diagnostics (OED) capabilities on all new vehicles. These diagnostic systems monitor the performance of engine and emission system components and inform the vehicle operator when component or system degradation could significantly impact emissions. Acceptable operation of the monitor requires proper treatment of system variables. Fuel composition is one of many possible variables that must be considered for monitoring components directly in the exhaust stream. Recently, the octane enhancing, emissions reducing additive methylcyclopentadienyl manganese tricarbonyl (MMT) was reintroduced into unleaded gasoline in the U.S. Prior to reintroduction, the additive underwent extensive testing to demonstrate that use of MMT does not adversely affect vehicle emissions or the operation of emission systems such as OBD. However, questions have been raised about the influence of the additive on OBD systems.