Cadillac DTS won't start

How long did it sit? The fuel could be bad.

PULL A FUEL SAMPLE FROM THE FUEL RAIL IN A GLASS JAR. IF HAS A SMELL THE GAS IS BAD OR IT LOOKS LIKE TWO DIFERENT FLUIDS THATS WATER. YOU WILL HAVE TO REMOVE THE FUEL TANK TO DRAIN IT. NEXT TIME USE STAYBIL.

You should be able to hear it run for a couple seconds a key on. 18 months is a bit long, but it should still run on that fuel, unless of course it was sub-standard fuel 18 months ago. There is a fuel pressure test port on the fuel injector rail. Aside from having a test gauge, you may be able to see if fuel is present(under pressure) by depressing the core at the test port, it is like a tire valve core. If there is pressurized fuel behind it after key on, or crank, that is one thing, but is the pressure adequate, is another concept. In the trunk, under the floor liner, there is a bolt on panel in the forward RH(passenger) corner. Under that panel is the fuel pump module(at the tank). You can check power and ground at that connector, use a volt meter or test light, across the gray and black terminals. The light should light, or you will see voltage, only for a couple seconds at key on, or during cranking(which may require the use of a second person). If you can confirm power and ground at the pump, you have verified the relay, and the PCM control of the relay. At that point, replace the pump AND filter. To answer your question from the original post, the powertrain control module is in the air cleaner housing.

Also pour fuel in the trottle body and see if it cranks and run as you feed it. Just pull a fuel sample from the valve on the fuel rail. If the fuel smells or you use a hose to pull a sample. Then youll know what your dealing with. There is nothing you can just add you need to drop the tank and flush it. Then you run a addive to clean up all the vasnish that happening.