Purchased and installed in May 2014. My car worked fine for the next few months, but then I noticed my check engine light came on. P0421 was the code. We took every troubleshooting step for this code and finally had to bring it to the store. A $90 diagnosis later, they assured me that the thing was still out of service six months after using it. To add to this, when I called Pacesetter to try and get them to redeem the guarantee for this, the guy I spoke to was controversial and didn't agree…