Blazer Forum - Chevy Blazer Forums

i have a 99 blazer 4 door 4x4 with W engine code and ooo a month ago my ses light came on and i hooked it up the the machine and it said Catalyst System Efficiency below Limit - Bank No 1... i changed my o2 sensors back in julybut only changed 2, and i was reading a forum and swartlkk said somthing about a 95 having 4 ... then last night on my way home from a christmas thing the light came back on so i ran to work and checked it out and it was that same dam code.. so i figured that my o2 sensor went bad so i warrantyed it out and changed it right theanir in the parking lot... and now this morning the same code came back on kinda flustered... any one with this same problem or any suggestions? thanks and have a marry christmas!!!