OBD CODE PO422 - MBWorld.org Forums

Feb 19, 2020 | 08:45 AM

heespaul

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1991 300sel

OBD CODE PO422

I OWN A 1997 S500 153,145 MILES. MY ISSUE STARTED WITH AN ENGINE LIGHT ON. THE OBD CODE INDICATED A BAD UPSTREAM LEFT SIDE O2 SENSOR. I DECIDED TO REPLACE ALL OF THEM AT ONCE INSTEAD OF ONE AT A TIME. ALL WAS GOOD AFTER REPLACEMENT FOR ABOUT A WEEK WHEN THE ENGINE LIGHT CAME ON. THIS TIME THE OBD CODE WAS A "422" AND DESCRIBED THE CATALYST EFFICIENCY IS BELOW THE NORMAL TRESHOLD IN THE 1ST ENGINE BANK, GENERALLY THE BANK HOUSES THE #1 CYLINDER". THIS SEEMS VERY AMBIGOUS TO ME BUT I ASSUME IT RELATES TO A FAULT IN EITHER THE 02 SENSOR OR A BAD UPSTREAM LEFT CATALYTIC CONVERTER. MY INITIAL THOUGHTS WERE THAT THE MECHANIC FAILED TO COMPLETE THE PLUG CONNECTION ON A SENSOR PLUG CAUSING THE RANDOM ON/OFF OF THE ENGINE LIGHT. IF NOT THEN I DON'T KNOW IF IT'S A BAD CATALYTIC CONVERTER, A DEFECTIVE SENSOR OR WHAT. I'M GOING TO THE SHOP TO VERIFY IF THE UPSTREAM LEFT SENSOR PLUG IS LOOSE OR DAMAGED.
IF IT'S NOT THAT THEN I NEED SOME ASSITANCE ON HOW TO DIAGNOSE THE PROBLEM. IS THERE ANYTHING THAT IS NOT O2 SENSOR OR CATALYTIC CONVERTER RELATED WITH THIS CODE? CAN A SENSOR BE TESTED USING AN OHM METER ELECTRONIC TESTER? IF IT ISN'T A SENSOR ISSUE THEN I NEED TO DETERMINE IF IT'S A BAD CATALYTIC CONVETER. DOES THE 422 CODE MEAN ITS THE UPSTREAM CONVERTER ON THE LEFT SIDE OR THE #1 CYLINDER SIDE UPSTREAM CONVERTER? ANY HELP DIRECTING ME TO FINDING WHAT I NEED TO CHECK,TEST AND THEN FIX WOULD BE GREATLY APPRECIATED.

I WANT TO THANK YOU ALL IN ADVANCE FOR YOUR ASSITANCE AND HELP. CHEERS, PAUL
P.S. PLEASE EXCUSE MY ALL CAPS BUT MY TYPING IS PATHETIC.

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