* Weak Battery: The most common cause. Even if the starter spins, a weak battery might not provide enough power to turn the engine over, especially if it's cold or the engine is difficult to turn (e.g., high compression engine).
* Bad Battery Connections: Corroded or loose battery terminals or cables will restrict current flow, even if the battery itself is good. Clean and tighten them.
* Failing Starter Motor (though unlikely in this scenario): While the starter is spinning, internal components might be failing. A weakened gear or solenoid could still spin the motor but fail to engage the flywheel adequately. This is *less likely* if you're getting a good spin.
* Low Compression: If the engine has low compression (due to worn piston rings, valve issues, etc.), it will be hard for the starter to turn the engine over. You might hear the starter struggling, but the engine won't catch.
* Fuel Delivery Problems: The engine won't start even if the starter cranks if it isn't getting fuel. Check for a clogged fuel filter, fuel pump failure, or other issues in the fuel system.
* Ignition System Problems: Spark plugs, ignition coil, distributor (if applicable), or crankshaft position sensor malfunctions can prevent ignition, even if the engine turns. This often results in no sputtering or firing sounds.
* Timing Belt/Chain Issues (serious): A broken or severely slipped timing belt or chain will prevent the engine from turning over. This is a serious mechanical problem that requires professional attention.
* Engine Seized: In rare cases, the engine could be seized due to a lack of lubrication or a major mechanical failure. This will require a significant repair.
Troubleshooting Steps:
1. Check the battery: Have the battery tested at an auto parts store to ensure it's holding a charge and has enough cranking amps.
2. Inspect battery terminals and cables: Clean any corrosion and tighten connections.
3. Listen carefully during cranking: Does the engine sound like it's struggling to turn over (low compression) or is it making unusual noises?
4. Check for fuel: Can you smell fuel? Is there fuel in the tank?
5. Check the ignition system: (This often requires more technical knowledge.) Consider having this checked by a mechanic.
If the starter spins readily but the engine won't catch, the problem is *likely* not the starter itself, but rather one of the other systems mentioned above. Start with the simpler checks (battery, connections, fuel) before moving on to more complex diagnostics. If you're not comfortable working on your vehicle, take it to a mechanic for diagnosis and repair.
