the service engine light came on awhile ago and it gave off a code for an O2 sensor. it wasn't mine yet so i didn't think anything of it, but i looked for the part recently and search results came back for sensors before the catalytic converter and a different one the goes after the cat. are there actually 2 of them? i imagine there would be different codes if there was more than one, but i've had it read twice and neither guy could give me a definite answer. i haven't really looked for it, so i thought i should start here. any advice would be a great help. it's a naturally aspirated series II 3800 in a 99 gt. also, it gave a code for a mass air flow sensor when i had it read today as well, would a new O2 sensor fix that or am i have to buy both parts?
