how much does it cost to fix abs system? on 2002 GMC Yukon XL 1500

It sounds like a motor is still running even after my engine is turned off--the repair shop says its the motor that runs the abs system.

Asked by for the 2002 GMC Yukon XL 1500
Some tests will need to be run to know for sure what is wrong. We would be willing to test it for free if you call me after 8 am this morning at 253-833-8161. Thanks, Greg. Sorry- forgot to mention we do have the factory GM diagnostic tool and offer a 3 year 36,000 mile warranty on our work.