I have a friend with a 2004 CTS 3.6 Sedan with under 30K on it. The car recently started making a lot of engine knocking and shacking a good bit. At first I thought it was maybe some bad gas, so I added some fuel system treatment along with some fuel stabilizer, that did not seem to work. Then, since it is usually driven in the city, I took it on the highway to clear it out. That seemed to do the trick, but only temporarely. Yesterday my friend started up the car in the morning and the front end and motor just shook horribly, so he shut it down and had it towed to a local Cadillac dealership. When it got to the dealership it would not start. Upon further analysis they determined that there was not any oil in the engine, they said they checked the dipstick and cylinders, nothing. Now, in all fairness, my friend did tell me that there is a possibility he has not changed the oil in the car in about 2 years, but I am not sure if the car just ran out of oil and it burned it up over 2 years or what. So, long story, the engine seized up, the codes that came up were errors concerning the camshaft and such. The only time the engine light came on or any warning for that matter was right when it was started the last time, when it was towed. In short he is looking at a new engine for about $8,000.00. Cadillac stated this is not under warranty because my friend did not maintain the car as he should have. The claim is in dispute with GM right now. Any ideas please post.