borla full exhaust
 

Hello guys, I want to know if i buy full exhaust borla system ( FR-S/ BRZ 2013 EL Headers part # 17285 and FR-S/ BRZ 2013 Cat-Back™ Exhaust part # 140496 ) and install it.
does it make my car's check engine light to turn on ?
is it bad to drive with car's check engine light on ?
do i need to tune my car's ecu ?

(sorry for my bad english)

It's likely because the 02 sensor is picking up higher values without a cat. I would disconnect the negative terminal from the battery and see if it clears. If not, some people on here added washers to the 02 sensor or you could get a tune that clears the CEL. It won't do any harm to the car. Or you could always sell me your cat-back!

tune that clears the CEL

I think the first O2 sensor is important and it send data to ecu.
does it turn off the second O2 sensor or something ? or just optimize it for headers without cat ?

The first O2 sensor is what the ECU uses to monitor AFR. The second O2 sensor is the one that measures for cat efficiency. You have a couple options (some better than others)

You can get an O2 extension and extend the second O2 sensor further out of the exhaust path. This usually works but the car still will not run properly due to the fact that the engine has not be tuned to run with the header.

Your best choice is to get a tuning solution that will eliminate the CEL from cat inefficiency. Vishnu's openflash tuner does this and you will also get a map to flash onto your car's ECU that will adjust it for better horsepower, thereby taking advantage of your header. There are other tuning options available, but I have no first hand experience with them. The stage 2 map with the OFT and headers gave a nice increase in horsepower as well removing that CEL for me.

All of them give HP and TQ with a tune. I would bet that most if not all, will give very little to no gains (perhaps even a drop in performance) without a tune.