Impact of Fuel Sulfur on OBD-II Catalyst Monitoring Using the Dual Oxygen Sensor Approach

Three vehicle and dynamometer-aged converters were evaluated for performance using the warmed-up portion (termed the “hot-18” cycles) of the Federal Test Procedure (FTP) and during a steady-state cruise using low and high sulfur content fuel. During the steady-state tests the catalyst performance was also monitored using two oxygen sensors designed to satisfy Phase II On-Board Diagnostics (OBD-II) requirements for vehicles sold in California in MY 1994 and thereafter. The performance of two of the converters decreased significantly upon switching to the high sulfur content fuel, and one of the converters which was diagnosed as passing with low sulfur fuel was diagnosed as failing with high sulfur fuel.