1. Identify Your 4WD System:
* Shift-on-the-fly (Electronic): This allows you to engage 4WD while the vehicle is moving (usually below a certain speed). It's controlled by an electronic module and actuator. This is the most common type in the '96 Blazer.
* Shift-on-the-fly (Manual): Similar to electronic, but you manually engage the 4WD using a lever or knob. The actuator still plays a crucial role in physically engaging the components.
* Part-time: Requires you to stop the vehicle before engaging 4WD.
2. Visual Inspection:
* Locate the Actuator: This is usually near the transfer case, often under the vehicle. Consult your repair manual for the precise location. It's typically a cylindrical device with wiring connected.
* Check for Obvious Damage: Look for any signs of damage such as broken wires, loose connections, leaks (especially if it has hydraulics), or physical damage to the actuator itself.
3. Testing (Electronic Shift-on-the-Fly Systems):
This is the most complex method. You will likely need a multimeter and a repair manual with wiring diagrams.
* Check for Power: With the ignition ON, use your multimeter to check for power at the actuator's connector. Your repair manual will show you which wires carry power and ground. A lack of power might indicate a problem with the wiring or the control module.
* Check for Continuity: With the ignition OFF, disconnect the connector from the actuator. Check for continuity (electrical connection) between the appropriate terminals on the connector according to your wiring diagram. A lack of continuity indicates a problem within the actuator itself.
* Check for Ground: Ensure a good ground connection to the actuator.
* Use a Scanner (Recommended): A professional-grade OBD-II scanner can often retrieve diagnostic trouble codes (DTCs) related to the 4WD system. This will pinpoint potential problems much more efficiently than manual testing. Many auto parts stores offer free code reading.
4. Testing (Manual Shift-on-the-Fly & Part-time Systems):
* Manual Engagement: If you have a manual system, try engaging 4WD. Listen for any unusual noises (grinding, clicking, etc.). If it doesn't engage smoothly, the actuator might be faulty.
* Visual Inspection During Engagement: If possible, have someone operate the 4WD shift lever while you visually inspect the actuator for movement or any binding.
5. Troubleshooting:
* Wiring Harness: If you find a problem with the electrical system, thoroughly inspect the wiring harness for breaks, shorts, or corrosion.
* Transfer Case: A problem within the transfer case itself might manifest as a 4WD actuator issue. This requires a more involved diagnostic process.
Important Notes:
* Repair Manual: A factory service manual for your specific year and model Blazer is invaluable for this procedure. It will contain detailed diagrams, specifications, and diagnostic steps.
* Safety: Always use jack stands when working under the vehicle. Disconnect the battery's negative terminal before working on any electrical components.
* Professional Help: If you're not comfortable performing these tests, it's best to take your Blazer to a qualified mechanic. Misdiagnosis and improper repair can lead to serious damage to your vehicle's drivetrain.
Remember, this is a general guideline. The specific testing procedure might vary slightly depending on your Blazer's exact configuration. Consult your repair manual for the most accurate and detailed information.
