How to Diagnose the Speed Sensors on ABS Wheels

Wheel sensors relay the wheel speed to a car's ABS electrical braking computer. Once the computer determines the wheel speed, the ABS braking computer will relay the proper braking percentage to the wheels to prevent skids and uneven braking. Over time, excessive vibration and wear can keep the wheel sensors from working properly. Once that happens, the ABS computer can not relay the proper braking percentage to the wheels. Diagnose and repair any problems that may exist with the speed sensors.

Instructions

1

Loosen the lug nuts from the front wheels.

2

Jack the front of the vehicle up and place the jack stands under the proper jacking points. Lower the vehicle to the top of the stands and leave the jack in place.

3

Finish removing the lug nuts from the front wheels. Pull the front wheels off and place them down flat near each work area.

4

Move to the driver side front wheel hub and locate the access hole on the front of the brake caliper. Slide the flat end of a flathead screwdriver through the hole and between the brake rotor and the inside brake pad. Pry the inside brake pad away from the brake rotor about 1/8 of an inch.

5

Loosen and remove the brake caliper mounting bolts on the back of the brake caliper. Pull the brake caliper off of the rotor and hang the caliper on one of the suspension components behind the wheel hub with a bungee cord.

6

Locate the wheel sensor that sticks through the spindle backing plate. Use a flashlight if necessary. Inspect the distance from the end of the wheel sensor to the front of the start wheel that attaches to the brake rotor. The distance should measure between 1/16 of an inch and 1/8 of an inch. Use the measuring tape if necessary. Remove the single mounting bolt and the strap from the wheel sensor wiring harness.

7

Follow the wiring harness from the back of the wheel sensor and inspect the wires for any cracks, chafes or breaks. Unhook the plug that connects the wheel sensor and the wiring harness with your hands. Pull the wheel sensor through the back of the spindle and out through the wheel well.

8

Inspect the front of the wheel sensor surface for dirt, metal shavings and excessive wear. If the front of the sensor has a build up of dirt, brake dust, or metal shavings, clean the front of the sensor with a clean rag and brake cleaner. If the front of the sensor has excessive wear, it will not correctly relay the information back and forth to the computer and the sensor will require replacement. When the sensor gets pushed in fully through the spindle and the distance from the front of the sensor to the star wheel measures more than 1/8 of an inch, replace the sensor.

9

Inspect the wiring harness plug for any cracks or breaks. Reconnect the wiring plug from the harness to the wheel sensor wiring plug. Push the wheel sensor through the spindle and until the front of the sensor measures between 1/16 and 1/8 of an inch from the tip of the sensor to the front of the star wheel.

10

Clean the front of the star wheel and the brake rotor with brake cleaner. Use a clean rag to wipe away the excess brake cleaner. Reconnect the brake caliper over the brake rotor and screw the bolts in tightly. Torque the caliper mounting bolts down to 50 foot pounds.

11

Slide the wheel back onto the wheel hub and screw the lug nuts on tightly. Jack the vehicle up and remove the jack stands. Lower the vehicle to the ground and finish tightening the lug nuts.

12

Move to the passenger side front wheel and the rear wheels if necessary and repeat the same process as outlined in the steps above to properly troubleshoot and diagnose the ABS wheel sensors.