SOME VEHICLES MAY EXPERIENCE THE CHECK ENGINE LIGHT ON WITH DTC P0421:00 (CATALYTIC CONVERTER SYSTEM) WITHOUT EXPERIENCING POOR ENGINE PERFORMANCE OR MISFIRE (MITSUBISHI PCM ONLY). THIS IS CAUSED BY IMPROPER CONTROL LOGIC OF THE PCM THAT MAY DETECT FALSE ERROR OF THE A/F SENSOR, RESULTING IN FALSE DETECTION OF P0421. TO CORRECT THE PROBLEM, THE CONTROL LOGIC OF THE PCM HAS BEEN CHANGED. CATALYST MONITOR FUNCTION EXPLANATION • THE PCM MONITORS THE OXYGEN STORAGE AMOUNT PROPORTIONAL TO CATALYTIC CONVERTER PURIFICATION CHARACTERISTIC. • THE PCM STARTS TO MONITOR AFTER RECOVERY (FUEL INJECTION STARTS) FROM FUEL CUT CONTROL. • THE PCM TEMPORARILY CHANGES THE TARGET AIR/FUEL RATIO TO RICH AT FUEL CUT RECOVERY, AND DETECTS THE RESPONSE TIME UNTIL THE HO2S OUTPUT SIGNAL OUTPUTS THE VOLTAGE ON THE RICH SIDE. • IF THE CATALYTIC CONVERTER PURIFICATION CHARACTERISTIC DETERIORATES, THE AMOUNT OF THE TIME UNTIL THE HO2S DETECTS THE VOLTAGE ON THE RICH SIDE IS SHORTER COMPARED TO THE NORMAL PURIFICATION CHARACTERISTIC AS SHOWN. THE PCM DETECTS A CATALYTIC CONVERTER MALFUNCTION USING THIS CHARACTERISTIC.
