After three repairs for a non-operative roof (the sensors went bad three times) my 2006 Cadillac XLR has an engine knock. It was diagnosed by the dealer as "inappropriate spark detonation" the problem has still not been solved even after three more visits to the dealer and a "site visit" by Cadillac's engineer. The car has been out of service for nearly a month since I purchase it, with no end in sight. I also own a new Cadillac STS, and there is no comparison between the cars. It is a shame that Cadillac cannot seem to get it right. Next time, it'll be a Mercedes-Benz SL500.
Build quality vehicles and provide better customer support.