Chk eng light is on again. This year its the exh manifold/cat. Whats going on? on 2002 Toyota RAV4

Ive had my car since may 02. I did all the computer recalls..even took care of the transmision slipping problem. Thank goodness i didnt have to comeup with the cash for that job. chk eng light is always on..its been on since 02 pretty much. Last time for my inspection it was o2 sensors.. before that fuel sensors... This time it is the exh manifold/cat. I get car is old..fragile..whatever. but what the heck with the light always on? It wont pass inspections..its making me crazy.

Asked by for the 2002 Toyota RAV4
alot of people put a piece of tape over the light so it doesn't annoy them. fix whats wrong to pass emisions...
Light doesnt bother used to it.. i have to fix the problem..theres no bypassing that. Just wondering why all the problems in the same area of the exhaust. O2 the manifold/cat. Thats the annoying part