I have a check engine light on a 2001 C70. I took it to advanced auto parts they ran the code and it came o2 sensor. They said it was the one behind the cat. I have put in a chip from speed tuning. Does the chip affect the o2 or cause it to go bad? I took it to place where is all the work on is Volvo. He said that some times the front o2 may not be working right and the back one is working to hard, giving a bad reading. In the end might have to replace both to get the light to stay off for good. Has anyone heard of this? Each are OME are $300 and Bosch Universal $80. Does the Universal work just as good? Thanks Jeff