Service Light Questions

hey i have a 1997 4x4 Tahoe and i just recently put flow masters on and about 3 months after i put the excaust on my service light comes on. So this morning i took my truck to a service center in town and the man tells me that my oxgen flow senser is messed up or somthing. But the thing is he says that its pass my caulter converters. Does anyone know what i should do or if that is even my problem???

I would find out what O2 sensor has gone bad, probably just needs to be changed. I did the same thing to my 97 K1500 p/u and never had any problems like this. Get the trouble code and search the fourms for it, you should find other instances, or just post it back here and I will see what the code means. Hope this helps.