Abs light is on? 2004 chevy avalanche

What i've seen with the k series chevrolet trucks is that the wheel speed sensors develop corrosion where the sensor mounts to the hub. you can start by taking the sensor out and cleaning off the mounting surface with a wire brush. the process is:

1. raise front of vehicle onto jackstands
2. remove front wheels
3. remove the brake caliper, bracket and rotor on both sides
4. remove wheel speed sensor via 1 torx bolt (be carefull as the corrosion will cause the sensor to "stick" in the hole)
5. clean the mating surfaces with a wire brush so the sensor bolt hole and mounting surface on the hub is shiney again.
6. if you can, pick up a can of rust preventing primer and spray a little on the surfaces to prevent further corrosion
7. let paint dry
8. apply a thin fil, of grease to the sensor and the sensor mounting spot on the hub
9. re-install sensor
10. revers steps 3-1 for re-installation.

*process is the same for both sides.

this was a common problem on the k series trucks.

while your in there it wouldn't be a bad idea to check the sensors wires to make sure they arent broken. let me know if the repair works for you

Your vehicle’s computer system has self-testing capability. When the computer senses that there is a problem with some of the components it stores the correspondent trouble code(s) in its memory and lights up the Check Engine, Service Engine Soon, ABS Or TC lights to tell you that there is a problem and you should have the car diagnosed and repaired. I would take it to a service center you trust and let then come up with a solution. Sometimes a problem in one system will turn light on for other systems that communicate with it, but it doesn't mean there is a problem in all of the systems.

Check codes first