Why is my car's ABS warning light always on?

Is this a problem?
by Ferman Lao | Sep 15, 2017

Good day!

I'm an avid fan of Top Gear Philippines! Thanks to you guys, I always get updated on what the latest automotive trends are. I have a problem and I thought you could help me with it. I did some research, but I just wanted to hear it from the best. The ABS warning light is always on even while I'm driving. Is that normal? Would other components be affected if  the ABS warning light remains on while driving? If there's a problem, will it cost much to repair?

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Hi Cocoa147,

Thank you for being a long-time fan and reader. We're glad to have you on board.

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No, it's not normal for your ABS warning light to be on.

In its most basic form, a modern ABS-equipped vehicle will have a wheel speed sensor for each of the wheel hubs, an ABS pump, an ABS control unit, and a warning lamp. The wheel speed sensor will have two primary components: The sensor (the stationary component with the wire coming out), and the tone ring (the ring with teeth). 

The warning lamp comes on to indicate that there is something amiss with the system. The control unit monitors the wheel speed sensors and activates the ABS pump accordingly, as called for by the speed sensor inputs.

The usual suspect for the warning lamp coming on is a broken sensor wire or a loose sensor connector. In both cases, the ABS control unit fails to read the sensor and will not activate the pump.

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Another cause is some contaminant in between the sensor and the tone ring. The sensor won't be able to give the correct signal (if at all) and the ABS system will be non-functional.

Another possible cause for failure is when the gap between the tone ring and sensor is incorrect. This usually happens when an incorrect replacement wheel bearing is used, or some other work is done which changes the gap between the two parts resulting in no signal from the sensor.

A failed pump or control unit will also cause the system to deactivate.

Unless the ABS sensor is tied into some other functions of the vehicle, like the vehicle stability control systems many modern cars have or the speedometer signal, there usually won't be anything else affected or any other warning lights present. The brake system should still be functional.

Repair costs can be as inexpensive as what it would take to clean the contaminants in between the tone ring or re-attaching the sensor connecter correctly, or as expensive as replacement of the ABS pump or control unit. It all depends on what's causing the system failure. Without knowing what vehicle you drive, we can't tell you. I know you think we're the best but we're not mind readers or prophets! Yet.

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Thanks for writing in!


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