See Figures 1, 2 and 3
The diagnosis of the ABS system is rather complex and requires quite a few special tools including scan tools, special test harnesses and other special and expensive tools. If the amber ABS light on the instrument cluster illuminates on your vehicle, check the fluid level in the master cylinder first. Low fluid level will usually illuminate the amber ABS light as well as, but not always, the red BRAKE lamp in the instrument cluster. The low fluid level could indicate a leak, but sometimes just indicates low, worn brake linings that have caused the caliper pistons and wheel cylinders to extend further, and thus using more fluid to exert force on them. Inspect the brake system for hydraulic fluid leaks and also inspect the brake linings for excessive wear.
Retrieving the Diagnostic Trouble Codes can be accomplished by the do-it-yourselfer with the proper scan tool. Attach the TECH 1-A scan tool or equivalent into the Diagnostic Link Connector (DLC) and follow the scan tool manufacturer's instructions to retrieve the DTCs from the ABS system.