If you're experiencing an issue with the ABS warning light coming on and the ABS being turned off in your 2000 Jeep Grand Cherokee, it could indicate a problem with the ABS system. Here are a few possible reasons:

1. ABS Sensor Issue: The ABS system relies on sensors located on each wheel to monitor wheel speed and detect any wheel lock-up. If one of these sensors is malfunctioning, it could trigger the ABS warning light. However, it is strange that your OBD2 scanner isn't showing any codes related to this issue.

2. Wheel Speed Sensor Wiring: The wheel speed sensors are connected to the ABS module through wiring harnesses. If there is a loose or damaged wire, it could disrupt the signal from the sensor and cause the ABS warning light to come on. Inspect the wiring harnesses to ensure there are no visible issues.

3. ABS Module Failure: The ABS module, which controls the ABS system, could be experiencing a malfunction. Sometimes, these modules can fail without throwing a specific code. In such cases, it might be necessary to replace the ABS module to resolve the issue.

4. Hydraulic Pump or Accumulator Problem: The ABS system also consists of a hydraulic pump and accumulator, which assist in applying and releasing brake pressure. If there's a fault with either of these components, it could trigger the ABS warning light.

Since you're not getting any specific codes from the OBD2 scanner, it might be challenging to pinpoint the exact cause of the issue. However, there are a few steps you can take to troubleshoot further:

1. Check the ABS System Fuse: Ensure that the fuse related to the ABS system is not blown or faulty. A blown fuse can cause the ABS warning light to illuminate.

2. Inspect for Wheel Speed Sensor Damage: Inspect each wheel speed sensor for any physical damage or debris buildup. Clean them if necessary and ensure they are properly mounted.

3. Check ABS Module Connections: Verify that all connections to the ABS module are secure and free from corrosion or damage.

If these steps do not resolve the issue, it might be best to consult a professional mechanic who can perform a more thorough diagnostic using specialized equipment. They will be able to pinpoint the specific cause of the ABS problem and recommend the appropriate repairs.