* Steering Wheel Lock: The steering wheel may be locked. Try gently jiggling the steering wheel while turning the key.
* Shift Lever Not in Park (or Neutral): Make sure the transmission is firmly in Park (or Neutral, if applicable). A slightly out-of-position shifter can prevent the key from turning.
* Faulty Ignition Switch: This is a common problem in older vehicles. The ignition switch itself might be worn out, damaged, or failing. This requires replacement.
* Broken or Worn Key: The key might be worn down or damaged, preventing it from engaging properly with the ignition cylinder. Try a known good key.
* Ignition Cylinder Issues: The ignition cylinder itself could be worn, damaged, or clogged with debris.
* Low Battery: While less likely to directly *prevent* the key from turning, a very weak battery can sometimes cause electrical issues that affect the ignition system.
* Security System Issues: If the Suburban has a factory or aftermarket alarm system, a malfunction could be interfering with the ignition.
* Other Electrical Problems: A broader electrical issue within the vehicle could be impacting the ignition system.
Troubleshooting Steps:
1. Check the obvious: Start with the steering wheel lock and transmission position.
2. Try a different key: Rule out a key problem.
3. Check the battery: A weak battery can cause strange electrical issues.
4. Listen for clicking: If you hear clicking sounds when you try to turn the key, it might indicate a low battery or a problem with the starter.
If none of these solve the problem, you'll likely need to have a mechanic diagnose the issue. A faulty ignition switch or cylinder is a common culprit and requires professional attention and replacement.
