* Vacuum System Issues: The 2000 Blazer likely uses a vacuum system to engage and disengage the 4WD. Leaks in the vacuum lines, a faulty vacuum switch on the transfer case, or a malfunctioning vacuum actuator on the transfer case are common causes. A leak could cause the system to randomly engage, while a faulty actuator might leave it stuck.
* Transfer Case Problems: A problem within the transfer case itself is possible. This could include internal linkage issues, a faulty shift motor (if it's an electronically controlled system), or even a broken shift fork.
* Wiring or Electrical Problems: If the Blazer has an electrically assisted or controlled 4WD system, a short circuit or faulty wiring in the system could cause the 4WD to engage unintentionally. This could include issues with the 4WD switch, related relays, or the control module.
* Low Fluid: Some 4WD systems rely on fluid pressure; although less common in this vintage Blazer, low fluid levels could be a contributing factor in sticking or unpredictable behavior. However, this is less likely to cause engagement when the vehicle is not in gear.
* Binding or Mechanical Issues: Something could be mechanically binding in the 4WD system, forcing it to stay engaged even when it shouldn't. This could be related to the linkage, the transfer case itself, or other components of the drivetrain.
Troubleshooting Steps:
1. Check the Vacuum Lines: Inspect all vacuum lines going to the transfer case for cracks, leaks, or disconnections. Repair or replace as needed.
2. Test the Vacuum Switch (if applicable): This switch controls vacuum to the transfer case actuator. Test it to ensure it is functioning correctly.
3. Inspect the Transfer Case Actuator (if applicable): Look for any visible damage or binding. Manually try to move the actuator linkage to see if it's freely moving.
4. Check the 4WD Switch and Wiring: Inspect the 4WD switch itself and the associated wiring for damage or corrosion. Use a multimeter to check for continuity and proper voltage if you're comfortable with electrical diagnostics.
5. Check the Transfer Case Fluid (if applicable): If the system uses fluid, check its level and condition.
Important Note: Attempting to diagnose and repair 4WD systems can be complex and potentially dangerous if not done correctly. If you are not mechanically inclined or familiar with these systems, it is highly recommended to take your Blazer to a qualified mechanic for diagnosis and repair. Improper repair can lead to further damage and potentially injury.
