Tests/Procedures: 1. Monitor the front and rear oxygen sensors while driving the vehicle at approximately 55 miles an hour. The oxygen sensors should cross-count consistently 8-10 times per 10 seconds.
2. Monitor the fuel trims for being normal at idle and at 55 MPH steady cruise.
3. Check the inlet to outlet temperature on the catalytic converter. Generally the rear should be 50 degrees, or more, hotter.