Abstract: Method and apparatus for monitoring a catalytic converter (32) during engine (catalyst) warm-up by first and second heated exhaust gas oxygen sensors (60, 70) located upstream and downstream, respectively, of the catalytic converter. A microprocessor determines a change of signal output of the downstream sensor relative to signal output of the upstream sensor during engine (catalyst) warm-up initiated by engine cold starting during the catalyst warm-up period. A catalyst light-off temperature is determined by the microprocessor when the change occurs. The catalyst light-off temperature thus determined is compared to a stored reference catalyst light-off temperature that is indicative of a properly functioning (e.g. fresh) catalyst to assess the extent or degree of degradation of the catalyst.

Abstract: A method and system for reducing time required for a catalyst to reach optimum operating temperature control an air/fuel ratio based on the catalyst temperature to supply excess air to the catalyst during closed loop lambda control. A lambda bias or offset is varied as a function of the catalyst temperature, engine speed, and engine load to bias the air/fuel ratio lean of the stoichiometric ratio. Excess air may be supplied to the catalyst for a predetermined period after a cold engine start or at any time that the catalyst temperature is below its optimum operating temperature for efficient conversion. The bias or offset is reduced to zero after the catalyst reaches a desired operating temperature or the predetermined time period expires.