Page 186 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

168 Methods for Monitoring and Diagnosing the Efficiency of Catalytic Converters

7) detecting deterioration of the main catalytic converter based on a first ratio of reversal
fiequencies of signals representative of emission levels provided from the second and third
airlhel sensors
8) determining a critical deterioration of the secondary catalytic converter when this first ratio
is higher than a predetermined value
9) hrther detecting deterioration of the secondary catalytic converters based on a second ratio
of reversal frequencies of signals representative of emission levels provided from the first
and second airlhel sensors
10) determining a critical deterioration of said secondary catalytic converter when this second
ratio is higher than another predetermined value.

The patent disclosure JP5321642 (1993) presents a similar method to this of US5233829
(1993) presented above.