Car Doctor Q&A: My Truck’s ABS is Always Working

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Anti-lock brakes have been in widespread use for 25 years now. It’s about time we all figured out how to fix them.

Q.I have a 2002 Chevy S-10 pickup truck that is a little rusty, dented and smells like a locker room. With all its problems, it does everything I need it to do. On weekends my little truck is very handy for trips to Home Depot and dump runs.

The problem is that from time to time the anti-lock brakes come on while I’m slowing down. This happens randomly with no sand or ice on the roads, just slowing down and then the brakes lock and release, making it a little hard to stop. I had a friend check over the brake system and didn’t see any problems.

Can I just disconnect the ABS brakes?

Find a Used Chevrolet S-10 at

A. Disconnecting the ABS system is not a great idea. It’s better to fix what’s wrong.

Most likely, you’ll be able to trace the issue to rust built up in the ABS wheel sensor, or sensors. Rust can build up to the point that it moves the sensor. The senor (or tone) ring can also be damaged or badly rusted.

Start by testing the sensors, which is fairly easy. The sensor operation is measured with a voltmeter set on the A/C millivolt scale:

  1. Safely raise the truck’s front end and remove the wheels.
  2. Locate the ABS sensor cable, which comes from behind the brake rotor.
  3. Unplug the cable at the connector in the wheelwell.
  4. Plug your multimeter’s probes into the male and female ends of the connector.
  5. Rotate the brake rotor quickly by hand.

The voltmeter should read over 350 millivolts. If the reading is less than 350 millivolts, start with removing the sensor from the hub and cleaning the mounting surface with a wire brush and sandpaper. Once all the rust is removed, reinstall the sensor.

If the voltage improves but still isn’t 350 millivolts the issue could be a faulty sensor or a very rusty wheel sensor ring.

This video does an outstanding job explaining the situation, the diagnostics and the repair on a Chevy in particular: