* Speed: You almost certainly need to be at a complete stop, or at a very low speed (virtually crawling) to shift out of 4-wheel low. Attempting to shift while moving, even slowly, can damage the transfer case. This is the most common cause.
* Transfer Case Issues: The transfer case itself might have a mechanical problem. This could include worn components, low fluid level, or a malfunctioning actuator (if it's electronically controlled). Low transfer case fluid is a major culprit.
* Shift Linkage: The linkage connecting the transfer case shifter to the transfer case itself might be bent, broken, or misadjusted. This would prevent the shifter from correctly engaging the 2-wheel high position.
* Vacuum System (if applicable): Some systems use a vacuum actuator to engage 4WD. A leak in the vacuum lines or a faulty vacuum actuator can prevent switching. Check for any vacuum leaks.
* Electrical Issues (if applicable): If your Blazer has an electronically controlled transfer case, there might be a problem with the shift motor, wiring, or related electrical components. This often manifests as the indicator light not working correctly or the transfer case not responding to the shifter.
Troubleshooting Steps:
1. Verify you're stopped: Absolutely ensure the vehicle is completely stopped before attempting to shift.
2. Check the Transfer Case Fluid: Locate the transfer case (usually toward the rear of the transmission) and check the fluid level. Low fluid is a common problem leading to shifting issues. If low, add the correct type of fluid (check your owner's manual).
3. Inspect the Shift Linkage: Examine the linkage visually for any signs of damage, bending, or looseness. If anything seems amiss, this needs to be addressed.
4. Listen for Unusual Noises: While attempting to shift, listen carefully for any grinding, whining, or other abnormal noises coming from the transfer case area. These noises indicate internal problems.
5. Check the 4WD Indicator Light: Does the light on the dash accurately reflect the position of the transfer case? If not, an electrical issue is suspected.
6. Try the "Neutral" Method (if applicable): If you can't shift directly from 4L to 2H, some suggest momentarily moving the shifter to "Neutral" before attempting to shift to 2H.
If you're not comfortable working on this yourself, take your Blazer to a qualified mechanic. Transfer case problems can be costly to repair, and attempting a DIY repair without the proper knowledge and tools can cause further damage. A professional mechanic can properly diagnose the issue and recommend the best course of action.
