Catalyst Monitoring

GENERAL DESCRIPTION

Catalyst monitoring is based on monitoring its oxygen storage capability.

The engine closed loop feedback control generates lambda (air/fuel ratio) oscillations in the exhaust gas. These oscillations are dampened by the oxygen storage activity of the catalyst. The amplitude of the remaining lambda oscillations downstream of the catalyst indicates the storage capability.

MONITORING PROCEDURE





In order to determine the efficiency the lean and rich time periods of the oxygen sensors up- and downstream will be compared.
The smaller of the two ratios determined is used for further processing.
The cycle counter is incremented by 1 after each cycle.
If the counter reaches a predetermined number of checks (235 lambda controller cycles) and the sum of all ratios determined is greater than a fixed value a fault will be stored in the computer memory.
The monitoring procedure is then terminated until the engine is shut-off and started again.





MONITORING STRUCTURE





Block diagram of system operation