What you're likely experiencing is a malfunction in the 4WD system, which could be due to several things:
* Transfer Case Problems: This is the most common culprit. Low fluid, worn parts, or internal failures within the transfer case itself can prevent it from shifting into 4WD.
* Speed Sensor Issues: The ABS speed sensors (located on the wheels) provide input to the system. A faulty sensor can confuse the TCM and prevent 4WD engagement.
* Shift Motor Issues: The motor that shifts the transfer case may be faulty or have low voltage.
* Wiring Problems: Damaged or corroded wiring between the sensors, transfer case, and TCM can cause intermittent or complete failure.
* TCM Problems: The transfer case control module itself can fail, requiring replacement.
Instead of trying to "reset" a sensor, you should diagnose the problem:
1. Check the Transfer Case Fluid: Low or dirty fluid is a very common cause. Check the fluid level and condition. If it's low, add the correct type (consult your owner's manual). If it's dirty, it needs a change.
2. Listen for Unusual Noises: When attempting to engage 4WD, listen carefully for any grinding, whining, or clicking noises from the transfer case. These often indicate a mechanical problem.
3. Check the 4WD Indicator Light: Is there a code displayed? If so, have it read by an OBD-II scanner to diagnose the specific fault code. This will point to the problematic area (sensor, motor, etc.).
4. Test 4WD Engagement: Try engaging 4WD on a safe, level surface. Does it engage? Does it disengage properly? Note any unusual behaviors.
5. Inspect Wiring: Visually inspect the wiring harness leading to the transfer case and sensors for any signs of damage, corrosion, or loose connections.
If you've checked these and still have a problem, you will likely need professional help. A mechanic with experience in 4WD systems will be able to properly diagnose the issue, which may require specialized tools and diagnostic equipment. Trying to "reset" something blindly could lead to further damage or misdiagnosis.
