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. Alternative methods and common sense can be substituted, however, it is beyond the scope of the average do-it-yourselfer. If you experience the amber ABS light on in the instrument cluster of 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.
The ABS module performs system tests and self-tests during startup and normal operation. The valves, wheel sensors and fluid level circuits are monitored for proper operation. If a fault is found, the ABS will be deactivated and the amber ANTI LOCK light will be lit until the ignition is turned OFF. When the light is lit, the Diagnostic Trouble Code (DTC) may be obtained. Under normal operation, the light will stay on for about 2 seconds while the ignition switch is in the ON position and will go out shortly after.
The Diagnostic Trouble Codes (DTC) are an alphanumeric code and a scan tool, such as Rotunda NGS Tester 007-00500 or its equivalent, is required to retrieve the codes. Refer to the manufacturer's instructions for operating the tool and retrieving the codes.
The Data Link Connector (DLC) for the ABS is located under the hood on models prior to 1995. On 1995-98 models, the OBDII connector located under the driver's side of the instrument panel, underneath the steering column, is used to retrieve the DTC's..
See Figures 1, 2, 3 and 4