you can get a good denso o2 for like 100 at autozone, same one that anyone would buy online and its better then OEM. make sure you get the one specifically for your car DONT get the universal one tht you have to cut wires. youre car came with 2 o2 sensors but the exhaust might have eliminated the rear one. in which case you would have a CEL unless you have DSMlink or something to fool the ECU.