* Bad battery: A weak or dead battery is the most common cause. Have the battery tested for voltage and cranking amperage at an auto parts store.
* Corroded battery cables or terminals: Check the battery cables for corrosion and clean them thoroughly. Loose connections can prevent sufficient current flow.
* Faulty ignition switch: The ignition switch might be malfunctioning and not sending power to the starter even though the key is turned.
* Neutral safety switch: This switch prevents the car from starting unless it's in park or neutral. A faulty switch won't allow the starter to engage.
* Alternator: While the alternator charges the battery, a faulty alternator might not be charging the battery adequately, leaving it too weak to start the engine.
* Incorrect starter installation: While less likely if you're comfortable with car repair, ensure the starter was installed correctly. A loose connection or improper wiring could prevent it from working.
* Ignition coil: A faulty ignition coil prevents spark to the engine.
* Distributor (if applicable): A problem within the distributor (like worn points or a bad rotor) could hinder spark delivery. (Older Bonnevilles may have distributors, newer ones use a distributorless ignition system.)
* Fuel pump or fuel delivery issues: The car won't start even if the engine cranks if it has no fuel. Check the fuel pump relay and fuses.
* Security system: If the car has a factory or aftermarket alarm or immobilizer, it could be preventing the car from starting.
* Engine issues: Something could be wrong with the engine itself preventing it from turning over even if the starter is working correctly (though a good crank usually indicates the engine is not the problem).
To troubleshoot, start with the simplest checks (battery, cables, and connections) and work your way through the list. A multimeter can be very helpful in checking voltage and amperage at various points in the starting system. If you're not comfortable working on your car's electrical system, it's best to take it to a mechanic.
