Several conditions create a no-start condition on a 1996 Cadillac Sedan Deville. The problem could be as simple as running out of gas to a complicated issue such as a computer problem. When diagnosing problems, start with the easiest set of problems first. Never “throw parts” at the Cadillac, as this form of guessing what the problem is costs more money than actually taking it to a shop to get it diagnosed.
Check the fuel gauge to make sure you have fuel in the tank. If you know the fuel gauge is not working, add fuel to the fuel tank to ensure that simply being out of gas is not the problem. Check the battery for power using a voltmeter. If the voltmeter shows less than 12 volts, charge the battery and try to start the vehicle. If it starts, measure the voltage with the voltmeter. If the voltage is between 13.5 and 14.5 with the vehicle running, the alternator is charging. If the battery runs down again, it has a bad cell and needs to be replaced. If the voltage is lower than 13.5, the alternator is not charging properly and needs to be replaced.
Check the starter if the battery and alternator are OK and you hear a "click" when you try to start the vehicle. If the click is definitely coming from the starter, the starter is bad. If the click is coming from the relay box, replace the starter relay.
Remove the Schrader valve on the fuel line. The fuel line runs along the top of the engine and has the fuel injectors attached to it. Place a rag under the fuel line at the Schrader valve. Press the Schrader valve in with the screwdriver, and at the same time, have the helper crank the Cadillac over once or twice. If the Cadillac is getting fuel and has fuel pressure, a stream of gas will shoot into the air. If fuel only dribbles or you don’t see any fuel, the problem is within the fuel system.
Pull one of the spark plug wires off the spark plug. Stick the extra spark plug into the spark plug wire. Lay the plug against metal (but not aluminum). Have the helper crank the Cadillac over three or four times. If you see a spark when the car cranks, the ignition system is working. If you do not see a spark, the problem is in the ignition system. This could include the coil, distributor or module.
Check the computer system if you have spark and fuel. Hook a scan tool up to the Cadillac’s computer system by plugging it into the port under and just to the left of the steering wheel. Press the “Read” button on the scan tool. If there is something wrong with one or more of the sensors, the scan tool will spit out codes. Write the codes down, then translate them using the code sheet that comes with the scan tool. Repair as required.
Check the computer. The computer cannot diagnose itself. If you plug in the scan tool and get several “strange” codes--for example, if the tool tells you that several sensors are bad, which is unlikely, or if the scan tool gives you a code that does not exist, there is a good chance that the computer is bad.
