I have a 2002 STS. I bought it in July '05. It had 47,000 miles on it. It too has some vibration at 65+ but I can live with it. The problem that just started two weeks ago is....I had it at the airport while I was in Detroit for some Super Bowl stuff. I got to the car after it was parked for three days and it wouldn't start. The lights worked strong, the bells were ringing just like normal but when I turned the key to start, the lights go off (like normal) but there is nothing. Not even a 'clicking'. I had it towed to the Caddy dealer and they replaced the battery (even though I told them the battery seemed fine). So it worked for about a week and a half and the same thing happed after it was parked in the garage overnight. Then the damndest thing happened, the next day I thought I would give it another try and it fired right up. So now I am afraid to take the car anywhere that I have to park because I may have to get it towed again. By the way, jumping did nothing. I tried that twice. Anyone familiar with this problem? Thanks.
Did the stealership test the battery??? I would start with a possible failing ignition switch...Any codes? I don't have an electrical schematic for your car but there also may be a relay involved.Pull the codes and see what the car is telling you.
i had this same problem in my eldorado, it was intermittent, one day it would start, one day it wouldnt....turned out my cables needed to be cleaned.and i had replaced the battery a month before thinking i had a problem with it and it turned out to be the starter. Had I cleaned the terminals at that time I would had been fine. Hence if the place who replaced your battery didnt do this, it prolly would had worked fine for a short time since taking the terminals off and putting back on would have cleaned them a tiny bit. If they are clean, I would make sure that they are not broken somewhere, or loose at the other end.