1. Check the Indicator Light:
* The most obvious first step: Your Blazer has a 4WD indicator light on the dashboard. This will illuminate when 4WD is engaged. However, a lit light *doesn't* guarantee proper 4WD function. It only means the system *thinks* it's engaged.
2. Listen for Transfer Case Engagement:
* Transfer Case Noise: When shifting into 4WD, especially low range (4LO), you should hear a noticeable clunk or engagement sound from the transfer case. This sound comes from the gears meshing. Absence of sound *could* indicate a problem.
3. Feel for Engagement (Careful!):
* Drive on a slippery surface: This is the most reliable test. Drive onto a loose surface like gravel, snow, or mud. Shift into 4WD (High or Low, as appropriate). If the 4WD is working correctly, you should feel a significant difference in traction compared to 2WD. The vehicle will feel more stable and less likely to slip or spin its wheels. Safety First: Perform this test in a safe, controlled environment.
4. Observe Wheel Rotation (Advanced):
* Jack up the front end (one wheel at a time): With the vehicle in 4WD, jack up one front wheel and one rear wheel. Rotate one of the front wheels. If the 4WD system is working correctly, the rear wheel should rotate in the same direction. (Caution: Use jack stands for safety, never rely solely on a jack).
5. Check the Transfer Case Linkage (Advanced):
* Visual Inspection: Look under the vehicle and check the transfer case linkage for any obvious damage or looseness. If the linkage is damaged, it could prevent the transfer case from properly engaging.
Important Considerations:
* Type of 4WD System: The 1999 Chevy Blazer likely has a part-time 4WD system. This means it's not intended for use on dry pavement. Engaging 4WD on dry pavement can cause drivetrain damage.
* Professional Inspection: If you're unsure or are experiencing problems, it's best to take your Blazer to a qualified mechanic. They have the tools and experience to diagnose any issues with your 4WD system.
By combining these methods, you can get a good idea of whether your Blazer's 4WD is functioning correctly. Remember to prioritize safety when performing any checks that involve driving or working under the vehicle.
