my check engine light came on so i did the whole paper clip in the connector trick and the light read a code 67. which ended up meaning-Catalyst system Efficiency Below Threshold malfunctioning or defective catalyst system.

I just got the whole exhuast system done with a hi-flow cat installed also. The thing is tho, the muffler shop that did it said that shouldnt have set it off. The dealership said the same thing. The only thing i can think it might be is the O2 sensor went bad. i no theres a code for that but is that even possible? and if it is because i got the cat put on, what do i do to make the check engine light go off. cuz reseting the computer gets old real quick...

 

bump

 

The Hi-Flow cat is your problem... I also did a free-flow cat on my 99 LS and it threw the same exact code... I never found a fix except to convert it to OBD1 or just put the stock cat back on...