1. Check the Simple Things First:
* Neutral: Is your transmission truly in neutral (or park)? The transfer case won't shift if the transmission isn't in neutral or park.
* Engine Running: Is the engine running? Some systems require this for the actuator to function.
* Shift Lever: Manually try to shift the transfer case lever out of 4LO. Is it stiff or impossible to move? This indicates a mechanical problem.
* 4HI: Can you engage 4HI (high range four-wheel drive)? If so, this suggests the issue is isolated to the low range selection mechanism.
2. Investigate Potential Problems:
* Shift Linkage: The linkage connecting the transfer case lever to the transfer case itself could be bent, broken, or disconnected. Inspect the linkage visually for any obvious damage. There may be linkage adjustment nuts that can become loose.
* Transfer Case Actuator: This is an electric motor that moves the shift fork inside the transfer case. It's a common point of failure. A failed actuator might not receive power, might be mechanically jammed, or simply be worn out. You might hear a clicking sound if it's attempting to operate but failing.
* Vacuum System (if applicable): While less common on 98 Blazers, some models use a vacuum system to assist with 4WD engagement. Check vacuum lines for leaks or blockages if applicable. This would require some mechanical knowledge and potentially a vacuum gauge.
* Transfer Case Internal Issues: This is the least likely culprit if 4HI works, but internal failure within the transfer case is possible. This would require professional diagnosis and likely repair or replacement.
* Electrical Problems: Check the fuses related to the transfer case. You may need a wiring diagram to identify which fuses are related to the transfer case actuator.
3. What to Do Next:
* If the lever is extremely stiff or immobile: Try working the lever gently back and forth a few times. If that doesn't work, you likely have a mechanical linkage problem requiring inspection and repair.
* If the lever moves but 4LO won't engage: The actuator is the most likely suspect. This will likely require testing the actuator with a multimeter to check for power and operation. Replacing the actuator is often the solution.
* If you're not mechanically inclined: Take your Blazer to a mechanic specializing in 4x4 vehicles. They can diagnose the problem accurately and perform the necessary repairs.
Safety Note: Don't attempt to force the transfer case lever. You could damage the linkage or the transfer case itself.
Remember to consult your owner's manual for specific diagrams and procedures related to your 1998 Chevy Blazer's 4WD system. Improper repair attempts can lead to further damage and potentially costly repairs.
