I am having a problem with the ABS on my car. When it happens, I floor it, and the car takes off just like it should. The car is accelerating correctly, and then all of sudden there is thumping and knocking. I try to brake, and the pedal pushes back and doesn't feel right. It sounds like a tire fell off a front wheel. I pull over and check everything out and it all looks normal.
Every time it has happened, the car was warm but had been sitting for about an hour, and I had only driven a couple blocks. There was no loss of traction, the rear wheels didn't break loose, and the car was driving straight. The first time it happened, I went to the dealer and they found nothing. The second time it happened, I pulled over and checked the lug nuts, the calipers, and touched the rotor--it was very hot. At that point, the car had been sitting for an hour and had been driven about 6 blocks. I think that the ABS is engaging by itself, while I accelerate hard, but otherwise for no reason. The brake pedal was not being touched when this happens. The traction control was on, but there was no reason for it to engage. After I back off on the acceleration, it keeps doing it. I drive the car hard but this must be a malfunction. Any ideas?
The wheel speed sensors are what sends the data of what the wheels are doing, and the ABS module receives and interprets this data. If one of these parts are not functioning properly, this could cause the ABS system to think that a wheel is slipping and engage the system.
The wheel speed sensors can be tested using a scan tool that shows wave lengths. These sensors work much the same way that a heart rate monitor works. It sends an up and down signal to the computer screen. Any variations in the wave length of one wheel as compared to the other wheels would indicate a malfunctioning wheel speed sensor.
If all wheel speed sensors are performing as intended, the likely cause would be an issue with the ABS module.
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