If a road test is needed for diagnosis, test for conventional (non-antilock) braking on a dry, clean, reasonably smooth and level roadway. This test cannot be accurately done if the roadway is wet, greasy, or covered with loose dirt such that all tires do not grip the road equally. Testing also may be adversely affected when the roadway is crowned, throwing the weight of the vehicle toward the wheels on one side, or when the roadway is too rough, making the wheels bounce. Test the brakes at different vehicle speeds, with both light and heavy pedal pressure. Note any unusual noises or handling symptoms.

Then test the brakes on a less than ideal road surface, such as one of gravel. The ABS mode will engage anytime a wheel locking tendency is detected by the control module. Thus, braking on gravel should cause the ABS to operate, resulting in rapid pulses felt through the brake pedal, and a slight popping or ticking noise heard from the pressure modulator valve assembly. During heavy braking on dry pavement, the tires may make chirping sounds intermittently as they approach lockup. This is less noticeable on wet or icy pavement, or on dirt or gravel roads.

Before road testing to diagnose (rather than confirm) ABS related symptoms, refer to the inspection procedures. Refer to ABS in Antilock Brake System (ABS) and Traction Control System (TCC)