Here's a breakdown of potential causes and troubleshooting steps:
1. Transfer Case Issues:
* Low Transfer Case Fluid: Check the transfer case fluid level. Low fluid can prevent engagement. If low, add the correct type of fluid (consult your owner's manual).
* Transfer Case Problems: Internal problems within the transfer case itself (worn gears, broken components) are a possibility, requiring professional repair or replacement. A mechanic can diagnose this with a more thorough inspection.
* Shift Linkage: The linkage connecting the transfer case shift lever to the transfer case might be broken, bent, or disconnected. Inspect the linkage for damage and ensure it's properly connected.
2. Front Axle Issues:
* Front Axle Disconnect: Some 1996 Blazers have a front axle disconnect system. This system allows the front driveshaft to spin freely when 2WD is selected. Make sure this system is functioning correctly and is allowing the front axle to engage in 4WD. This often involves vacuum lines and a vacuum actuator. Listen for the actuator engaging and disengaging.
* Front Differential Issues: Problems within the front differential (low fluid, broken gears) will prevent 4WD from engaging. Check the front differential fluid level.
* Front Driveshaft: Inspect the front driveshaft for damage, binding, or loose components. A broken or disconnected driveshaft prevents 4WD.
3. Electrical Issues (if applicable):
* 4WD Indicator Light: Is the 4WD indicator light on the dashboard functioning correctly? A malfunctioning light might indicate a problem with the electrical system controlling 4WD engagement. A non-lit indicator light may indicate a fuse or other electrical issue preventing 4WD from engaging.
* Vacuum System: The 4WD system in some years used vacuum to engage components. Leaks in the vacuum lines can prevent proper engagement. Inspect vacuum lines and the vacuum actuator for leaks or damage.
* Electrical Switch Issues: A faulty switch can prevent the transfer case from receiving the command to shift into 4WD.
4. Other Potential Issues:
* Incorrect Shifting Procedure: Make sure you are following the correct procedure for engaging 4WD. Your owner's manual will describe the specific steps to shift into 4WD (e.g., vehicle needs to be stopped, or only at low speeds, etc.).
* Binding or Obstructions: Check for anything that might be binding or obstructing the drivetrain, especially in the front axle or driveshaft areas.
Troubleshooting Steps:
1. Check fluids: Transfer case and front differential fluid levels.
2. Inspect linkages: Check the transfer case linkage for damage or disconnection.
3. Inspect driveshafts: Look for damage, loose components, or binding.
4. Check vacuum lines (if applicable): Inspect for leaks or damage.
5. Check 4WD Indicator light: Does it illuminate when you try to shift to 4WD?
6. Consult your owner's manual: It provides specific information on your Blazer's 4WD system, including shift procedures and troubleshooting tips.
If you're not comfortable working on your vehicle, take it to a qualified mechanic for diagnosis and repair. Attempting repairs without proper knowledge and tools can lead to further damage. Be sure to mention that it's a 1996 Chevy Blazer, this will help the mechanic better assist you.
