how do I service the suspension system on a 2007 Chevrolet Avalanche?

You need to start by diagnosing the problem. In this case you will need a good scan tool that can communicate with the abs system. If you don't have one, here is a link to find a shop near you that can help out. https://repairpal.com/repair-shops Alex

It is not a diy operation - seek qualified personnel for hands-on diagnosis.