Battery and Electrical System:
* Dead Battery: This is the most common cause. Check the battery terminals for corrosion and clean them if necessary. Have the battery tested at an auto parts store to determine its charge and overall health.
* Loose or Corroded Battery Cables: Even if the battery has a charge, loose or corroded cables can prevent the engine from cranking.
* Faulty Alternator: The alternator recharges the battery while the engine is running. A failing alternator will eventually drain the battery, preventing the car from starting.
* Faulty Starter Motor: The starter motor is responsible for cranking the engine. A failing starter can make a clicking noise when you turn the key, or it might not engage at all.
* Faulty Ignition Switch: This component allows power to flow to the starter. A malfunctioning switch will prevent the car from starting.
* Wiring Problems: A break or short in the wiring harness can interrupt the electrical flow to the starter or other critical components.
Fuel System:
* Empty Fuel Tank: Sounds obvious, but make sure you have gas!
* Fuel Pump Failure: The fuel pump delivers fuel from the tank to the engine. A failed pump will prevent fuel from reaching the engine.
* Clogged Fuel Filter: A dirty fuel filter can restrict fuel flow to the engine.
* Fuel Injector Problems: If the fuel injectors aren't spraying fuel into the cylinders, the engine won't start.
Engine Related:
* Distributor Issues (if equipped): Older vehicles often have distributors. Problems with the distributor cap, rotor, or ignition coil can prevent the engine from firing.
* Spark Plugs and Wires: Worn or damaged spark plugs and wires can prevent the engine from igniting the fuel-air mixture.
* Sensor Problems: Various sensors (e.g., crankshaft position sensor, camshaft position sensor) tell the engine's computer when to fire the spark plugs. Faulty sensors will cause starting problems.
Other Possibilities:
* Immobilizer System (if equipped): Some vehicles have anti-theft systems that can prevent the car from starting if the correct key isn't used.
* Security System Issues: A faulty alarm system might be preventing the car from starting.
Troubleshooting Steps:
1. Check the battery and cables: This is always the first step.
2. Listen for sounds: Does the starter crank? If you hear clicking, it could be a low battery, faulty starter, or bad connection. If there's no sound at all, it points to a more serious electrical issue.
3. Check the fuel: Make sure the tank isn't empty.
4. Check fuses and relays: Blown fuses or bad relays can disrupt electrical circuits.
5. Consult a repair manual: A repair manual specific to your 1991 Cadillac DeVille will provide detailed information about the electrical system and troubleshooting procedures.
If you're not comfortable working on cars yourself, it's best to take your DeVille to a qualified mechanic for diagnosis and repair. Describing the symptoms (e.g., clicking sounds, no cranking, etc.) to the mechanic will help them quickly pinpoint the problem.
