1. Issues Preventing Cranking:
* Dead Battery: The most common cause. Test the battery voltage. It should be around 12.6V when fully charged. A lower voltage indicates a weak or dead battery. Also check the battery cables for corrosion or loose connections.
* Bad Starter: The starter motor may be faulty, seized, or have worn-out components. A clicking sound when you turn the key is often a sign of a bad starter.
* Starter Solenoid: This is the relay that activates the starter. A faulty solenoid will prevent the starter from engaging. You might hear a clicking sound from the solenoid itself.
* Faulty Ignition Switch: This switch sends power to the starter. A broken or worn-out switch won't send the signal.
* Broken or Loose Wiring: Check all wiring connections related to the battery, starter, solenoid, and ignition switch. Corrosion or broken wires can interrupt the circuit.
* Neutral Safety Switch (Automatic Transmission): This prevents starting unless the car is in park or neutral. A faulty switch will prevent starting regardless of gear selection.
2. Issues Preventing Starting (Even if it cranks):
* No Spark: The engine won't start if there's no spark at the spark plugs. This could be due to:
* Faulty Ignition Coil: Provides the high voltage for the spark plugs.
* Bad Distributor Cap or Rotor (points distributor systems): These distribute the high voltage to the correct spark plug. Electronic ignitions are less prone to these issues.
* Worn or faulty spark plug wires: Cracked or loose wires will prevent proper spark delivery.
* Faulty Spark Plugs: Worn, fouled, or improperly gapped spark plugs won't ignite the fuel-air mixture.
* Ignition Control Module (ECM/PCM): In electronic ignition systems, the ECM/PCM controls the spark. A faulty module will prevent sparking.
* No Fuel: The engine needs fuel to run. Issues include:
* Empty Fuel Tank: The obvious one!
* Fuel Pump Failure: The pump doesn't deliver fuel to the carburetor or fuel injectors.
* Clogged Fuel Filter: Restricts fuel flow.
* Faulty Fuel Injectors (fuel-injected engines): Injectors may be clogged or electrically faulty.
* Problems with the Fuel Delivery System: Issues in the fuel lines, carburetor (if applicable), or fuel pressure regulator can interrupt fuel flow.
3. Other Possibilities:
* Timing Chain/Belt Issues: Severe timing issues can prevent starting or cause damage if the engine cranks. This is less likely to cause the engine to *not* crank, however.
* Compression Issues: Low compression in one or more cylinders will make starting difficult or impossible. This often requires a compression test to diagnose.
* Security System (if equipped): An anti-theft system could be preventing the engine from starting.
Troubleshooting Steps:
1. Check the battery voltage.
2. Listen for clicking sounds: This helps pinpoint starter, solenoid, or ignition switch issues.
3. Inspect wiring and connections for corrosion or damage.
4. Check fuel level.
5. Test for spark at the spark plugs.
6. Check fuel pressure (fuel-injected engines).
If you're not comfortable working on your car yourself, it's best to take it to a qualified mechanic for diagnosis and repair. Trying to diagnose these problems without the right tools and knowledge can lead to further damage.
