* Worn Key: Over time, keys wear down, especially if they've been used frequently or have been subjected to damage (bending, drops). The worn key's teeth may no longer precisely match the lock's tumblers.
* Worn Locks: The locks themselves can wear out, becoming less precise in their operation. Dirt, debris, and general wear and tear can affect the mechanism.
* Broken or Stuck Lock Mechanism: Internal parts of the lock mechanism might be broken or jammed, preventing the key from turning or engaging properly. This is more likely if you've experienced any forced entry attempts or if the lock has been subjected to significant impacts.
* Key Misalignment: Sometimes, the key isn't fully inserted into the lock. Ensure the key is fully seated before attempting to turn it.
* Incorrect Key: While seemingly obvious, make absolutely sure you're using the correct key for your car. It's easy to grab the wrong one from a keychain.
* Frozen Lock: In cold weather, locks can freeze, making them difficult or impossible to operate. Try warming the lock with a hairdryer (carefully!) or using de-icer spray.
* Lock Cylinder Binding: Dirt, debris, or corrosion can cause the lock cylinder to bind, preventing the key from turning.
* Security System Issues: Although less likely to completely prevent key use, a faulty alarm system or immobilizer could interfere with the locking mechanism.
What to do:
1. Try different keys (if you have spares): This helps rule out a worn or incorrect key.
2. Inspect the key for wear: Look for signs of significant wear or damage on the key's teeth.
3. Clean the key and lock: Use a compressed air canister to blow out any dirt or debris from the keyhole. If you have a key that fits well but requires some force to go in, some graphite powder (available from a hardware store) can improve the situation. *Never use oil* as it can attract and trap dirt.
4. Try gently jiggling the key: Sometimes a slight movement can help align the key with the tumblers.
5. Check for frozen locks (if applicable): Use a de-icer or warm the lock carefully.
6. If the key *does* turn but the lock doesn't engage, this indicates a mechanical problem within the lock itself.
If none of these solutions work, you'll likely need a locksmith or your mechanic to diagnose and repair the problem. They can determine if the locks need replacing, if the key needs replacing, or if there's a more serious mechanical issue.
