1. Check the Battery Connections:
* Clean the terminals: Corrosion on the battery terminals is a very common cause of starting problems. Use a wire brush or battery terminal cleaner to remove any corrosion from both the positive (+) and negative (-) terminals and the connecting cables. Make sure the connections are tight.
2. Battery Voltage Test:
* Use a voltmeter: A simple voltmeter is crucial. Test the battery voltage with the key OFF. It should read around 12.6 volts (a fully charged battery). If it's significantly lower (e.g., below 12 volts), the battery needs charging or replacing.
* Test voltage while cranking: Have someone turn the key to the "start" position while you monitor the voltage. The voltage should *not* drop significantly below 10 volts. A large voltage drop indicates a weak battery or a problem with the charging system.
3. Starter Motor Relay or Solenoid:
* Location: The starter relay (or solenoid, sometimes integrated into the starter) is usually located under the hood, often in a fuse box or near the battery. Consult your owner's manual for the exact location.
* Check for damage: Inspect the relay for any signs of burning or damage. If you can easily access it, you might try swapping it with another relay of the same amperage (use caution and only do this if you're comfortable with car electrical systems).
* Listen for a click: When you turn the key, do you hear a single click from the starter area? This could be the relay or the solenoid engaging but not engaging fully. This is often due to a weak battery, bad relay, or a failing starter.
4. Ignition Switch:
* Less likely: A faulty ignition switch can prevent power from reaching the starter. This is more complex to diagnose and often requires professional help.
5. Security System (if applicable):
* Check for immobilisers: Some Cadillacs have security systems that can prevent starting if there's a fault. Try any key fobs you have and make sure the key is properly recognized.
6. Neutral Safety Switch (Automatic Transmission):
* For automatic transmission cars: Make absolutely sure the car is in Park (P). A faulty neutral safety switch won't allow the starter to engage even if the car is seemingly in park.
7. Starter Motor (Most Difficult):
* Testing the starter: Requires expertise, the right tools, and safety precautions. It often involves removing the starter and testing it directly with a battery. This is best left to a mechanic.
When to Call a Mechanic:
If you're uncomfortable performing any of the above steps, or if none of them solve the problem, it's best to call a qualified mechanic. They have the tools and experience to diagnose the issue accurately and safely, especially if it involves the starter motor or ignition switch. Continuing to crank the engine with a known starting problem may damage the battery or starter.
