If a road test is needed for diagnosis, test for conventional (non-antilock) braking on a dry, clean, reasonably smooth roadway. This test cannot be accurately done if the roadway is wet, greasy or covered with loose dirt such that all of the tires do not grip the road equally. Testing also may be adversely affected when the roadway is crowned, throwing weight of the vehicle toward the wheels on one side. A rough roadway may also cause the wheels to bounce.

Test the brakes at different vehicle speeds with both a light and heavy pedal pressure. Note any unusual noises or handling symptoms.

After testing on an ideal roadway, test the brakes on a less-than- ideal road surface, such as gravel. The ABS mode will engage anytime a wheel locking tendency is detected by the control module. Braking on the gravel should cause the ABS to operate. This should result 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 a chirping sounds intermittently as they approach lock-up. This is less noticeable on wet or icy pavement, or on dirt or gravel roads.