How To Set The Air Gap For Wheel Speed Sensors And ABS

When you receive a new wheel hub assembly, you may be wondering how to set the air gap for the speed sensors. If you’re working with a modern wheel hub assembly, you most likely won’t need to do it. Read on to find out why.

What Do Wheel Speed Sensors Do?

wheel speed sensor

Wheel speed sensors are installed in pairs on both sides of the car in the hub. A vehicle has four wheel speed sensors: two in the front, and two in the rear. Wheel speed sensors detect when the wheel is rotating. They create a signal called a “wheel speed pulse”.

The ECU receives the wheel speed pulse. The ECU uses this information to display the vehicle’s speed on the dash. The ECU also sends this information to the Automatic Braking System (ABS) and Traction Control System (TCS).

How Does A Wheel Speed Sensor Work With A Tone Ring?

Tone ring

All new wheel hub assemblies come with a tone ring. Also called a reluctor ring, the tone ring is a notched or toothed ring. It works with the wheel speed sensor to determine the wheel’s rotation speed.

The wheel speed sensor is located adjacent to the tone ring in the hub. The sensor has a pole pin that’s connected to a magnet. When the tone ring passes by, its toothed edge cuts into the magnetic field around the pole pin. This causes the wheel speed sensor’s magnetism to vary as it rotates. The ECU reads this varying magnetic field and uses that information to determine how fast the wheels are rotating.

On older vehicles, a tone ring is not always included with a new hub assembly. In these cases, it’s important for mechanics to set the speed sensor air gap themselves. Air gaps are defined as “the space between 2 electrical contacts.”

If the air gap is not set correctly, the ABS and TCS will not work correctly. A warning light will most likely illuminate. Setting the air gap correctly will avoid these issues.

Why You Should Never Remove The Wheel Speed Sensor Or Tone Ring On A New Wheel Hub Assembly

Many technicians wonder if they can set the air gap by removing the speed sensor or tone ring. The answer is a resounding no. Joe Keen explains why in this video:

When you get a brand new wheel hub assembly, you should never remove the wheel speed sensor or the tone ring. It’s because the factory already set the air gap and tested it. This is only true with high quality wheel hub assemblies, though. Many low quality wheel hub assemblies have universal wheel speed sensors, and the air gap may not have been set correctly. It’s common to encounter problems with ABS and TCS with cheap wheel hub assemblies.

Your best bet is to always order high quality wheel hub assemblies. Be sure to install the new wheel hub assembly correctly As long as you use high quality wheel hub assemblies, your customers very likely won’t encounter any ABS or TCS issues.

At GMB, we produce only OE-quality wheel hub assemblies. All GMB wheel hub assemblies:

  • Are made with high quality materials and bearing grease
  • Come with OEM-spec wheel speed sensors and tone rings that have been thoroughly tested
  • Are made with triple and quadruple lip sealing technology


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