i had the resonator removed from the svt and i noticed that the check engine light will come on and stay on for about 3weeks then it goes off for maybe a week or 2. I finally decided to go to auto zone and find out why, the guy said that the oxygen sensor after the cat is what is causing the light to go on. So he reset it and the light is no longer on. any truth to this? or should i get a second opinion

98 T Red SVT CF hood and trunk, Vogtland springs, KYB struts, 8mm wires, KKM intake, BAT intake pipe, resonator removed, Steeda Short Throw, JVC MP3/WMA head unit, Alpine Type-S surround, 2 10in, Kicker subs, Soundstream amp,