ABS Brake Repair: How to Clean, Test, And Replace ABS Wheel Sensors
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ABS Brake Repair: How to Clean, Test, And Replace ABS Wheel Sensors

Dirty ABS wheel speed sensors and broken sensor wires are a major cause of the ABS "Idiot Light" coming on and remaining on. Cleaning and testing wheel sensors and their associated wiring is a straightforward project that even the new shade tree mechanic can do.

The Anti-Lock Braking System (ABS) consists of speed sensors, usually one on each wheel, a pump, four valves, and an electronic control module (ECM). A malfunction of any one of those components will activate the ABS "Idiot" light. A defective pump or ECM means substantial bucks, but an ABS light could mean nothing more than a dirty or defective wheel sensor. Dirty sensors might not be such a problem for city dwellers, but it is a significant problem for those who live out in the country where unpaved roads abound. Fortunately, cleaning, testing and replacing wheel speed sensors is something that any shade tree mechanic can handle.

Things That You Will Need

  1. A service manual for your vehicle. There are many good ones to choose from, but I recommend one by either Chilton or Haynes because they are written with the non-professional auto mechanic in mind. They assume nothing and omit nothing.
  2. A good basic set of mechanics hand tools.
  3. Lug wrench or a power impact wrench
  4. Hydraulic garage floor jack.
  5. A set of jack stands
  6. A digital Multimeter (DMM)
  7. Shop rags

Preparation

  1. Using a lug wrench or an impact wrench, break the wheel lug nuts free on all four wheels while the car's wheels are still on the ground.
  2. Raise the car with the hydraulic floor jack and support it on four jack stands. Place the floor jack and jack stands under the jacking and support point shown in your service manual. With the car supported on the jack stands, rock the car a few times to make sure it is securely supported and will not slip off while you are working on it. Never work on a car supported on a jack alone.
  3. Finish removing all four wheels.

Removing The Sensors

  1. Access the front wheel speed sensors by turning the wheel toward the opposite side of the car. When working on the rear wheel speed sensors, you will have to get under the car.
  2. Remove the two bolts securing it to the suspension. These bolts are set far back, so you will need to use a socket and an extension bar to reach them properly.
  3. Pull the sensor out and remove the two bolts securing the sensor line to the sensor.

Clean and Inspect The Wheel Speed Sensor

  1. Wipe the sensors clean with a clean shop rag. If they are really encrusted with road grime and you need to use a liquid cleanser, wash them off in a bucket of soapy water and then rinse them off with plain water. NEVER use any kind of chemical cleaning agent on wheel speed sensors.
  2. Inspect the wheel sensors for physical damage. Wheel speed sensors are relatively inexpensive to replace, so when in doubt about their condition, replace them.

Checking The Wheel Speed Sensors With An Ohmmeter

  1. Set your auto-ranging DMM to its "Ohms Function."
  2. Check your service manual for the exact resistance reading for a good wheel sensor. The typical sensor resistance is approximately 50 Ohms.
  3. Touch the meter probes to the sensor terminals.
  4. A reading of "Infinite" resistance indicates an open circuit and a bad sensor. A reading significantly higher or lower than the resistance given in the specification indicates a bad sensor. In either case, you need to replace the sensor.

If all the wheel sensors are clean, check out good mechanically and electrically, but you still have an ABS Light, check the wiring before you start thinking pump. Valves, or ECM. If the brakes are working OK, the odds are that all those components are OK. Check the wiring continuity from end to end. The wires may look OK on the outside but have broken conductors on the inside. A good wire has very little resistance. Most DMM will indicate a resistance of around 0.5 Ohms, which is the resistance of their internal fuse, not the resistance of the wire. A good wire will have almost no resistance of its own. Wheel sensor wires are easily damaged, especially if the car has been in a ditch or snow bank.

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Comments (4)

You are definitely the go-to guy for car information. Thanks for another terrific article!

Thanks, Gayle. Cars have been one of my passions ever since I restored my first car, an old 1932 Dodge Coupe, when I was fourteen years old. I found that old car under a mound of hay in one of my uncles barns. He gave it to me to amuse me, he never expected me to get it to run again. The body was in good shape but every thing else had been ravaged by age. I had to rebuild that car from the wheels up but by the time I got my learners permit two years later it was running like a top.

detailed and well written article

That ABS light used to come on constantly on my Camaro. It never was anything serious.

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