* Worn Ignition Switch: This is the most common cause. Years of use cause the internal components of the switch to wear down. The tumblers may become worn, sticking, or misaligned, preventing the key from turning smoothly or at all.
* Broken or Damaged Key: A worn, bent, or damaged key can fail to engage properly with the ignition switch mechanism, causing it to bind or lock.
* Steering Column Issues: The ignition switch is often linked mechanically to the steering column lock. A problem with the steering column lock mechanism (which prevents theft) can interfere with the ignition switch's operation. This could be a broken or jammed lock, or a binding column.
* Wiring Problems: Although less common, a short circuit or damaged wiring in the ignition system can sometimes affect the switch's ability to function correctly. This is less likely to cause a complete lock-up but could contribute to erratic behavior.
* Shift Linkage Problem (Automatic Transmission): On some automatic transmission vehicles, the ignition switch is interlocked with the shift lever. If the shift lever isn't fully in Park, the ignition switch may refuse to turn.
* Electrical Issues: While less likely to cause a complete lock-up, electrical issues, like a low battery, can sometimes affect the ignition system and make turning the key difficult.
Troubleshooting Steps (Proceed with caution):
* Check the key: Try a spare key if you have one. If the spare works, the problem is with your original key.
* Shift to Park (Automatic): Make absolutely sure your transmission is firmly in Park.
* Steering Wheel Position: Try gently jiggling the steering wheel while trying to turn the key. A slightly misaligned steering wheel can sometimes interfere with the ignition switch due to the steering column lock.
* Battery Voltage: Check your battery voltage. A low voltage could contribute to problems.
If none of the above works, you likely need professional help. Attempting to force the ignition switch can cause further damage. A qualified mechanic will be able to diagnose the specific problem and repair or replace the faulty component. Often, the entire ignition switch assembly needs replacement, which is a relatively straightforward repair for a mechanic.
