ABS Sensor

[bdomarat]

ABS on my 91 Taurus stopped working- it wont pulse the brakes. I tried removing one of the wheel abs sensors, removed the screw, then pryed the assembly and destroyed the shield I think. Put the screw back on, the ABS light is on all the time now. How do you remove the ABS sensor?

[shorod]

Hmm, the times I've had to pull the ABS sensors, I've just had to remove one screw and carefully wiggle the sensor loose from the hub. Many times, especially with aluminum hubs, the sensors will corrode into the aluminum and I will give a quick shot of penetrant, allow it to soak a couple minutes, then gently rotate the sensor to break the corrosion loose. Once it's broken loose, I rotate it back and forth while attempting to pull it out of the mounting hole. Haven't broken one yet.

On many of the GM's though, the ABS sensors are an integral part of the steering knuckly. If the sensor is bad, you have to replace the entire knuckle.

-Rod

[DonSor]

Concur with Shorod.

I replaced the ABS sensor on my 99 Ford Ranger which located on top of the differential. All I did was losen the clamp screw and pulled the sensor right out of the slot. Replaced with an OEM and experienced joy. Didn't know that some cars have it their steering knuckles. I know many all-wheels have them one in each wheel. I believe sensors have to sense auto speed, thus they are triggered by some sort of sensing wheel.

[LeSabre97mint]

Originally Posted by DonSor

Concur with Shorod.

I replaced the ABS sensor on my 99 Ford Ranger which located on top of the differential. All I did was losen the clamp screw and pulled the sensor right out of the slot. Replaced with an OEM and experienced joy. Didn't know that some cars have it their steering knuckles. I know many all-wheels have them one in each wheel. I believe sensors have to sense auto speed, thus they are triggered by some sort of sensing wheel.

I replaced a front wheel bearing on my 97 LeSabre. The ABS sensor is part of the bearing assembly.

The sensors work with each other. If all of the sensors on the wheels report the same speed every thing is fine. When one or more wheels slow or stop the ABS kicks in pulsing the wheel so the wheel can gain traction.

Regards

Dan

[shorod]

Originally Posted by DonSor

I believe sensors have to sense auto speed, thus they are triggered by some sort of sensing wheel.

Yep, that's exactly right. They use Hall effect to sense vehicle speed. There is a brittle toothed ferrite ring on the axle. This will likely be part of the halfshaft assembly if a drive wheel, or part of the hub on a non-drive wheel. The teeth rotate past a magnetic sensor, the ABS sensor, and output a square wave to the ABS computer. The frequency of the square wave corresponds directly to the speed of that wheel. In a four channel system (common today), each wheel can be controlled independently (and is often tied into a traction control system). For ABS, if one or more wheel(s) slows down more rapidly than expected, the ABS solenoids will modulate the brake fluid pressure to that wheel to allow it to rotate in a controlled manner. The opposite occurs for traction control. If a wheel speed sensor detects that a wheel is accelerating too rapidly, it will apply brake force to that wheel to slow it down and transfer the power to the wheel(s) getting traction. The ABS can also be activated based on data from G-sensors in the car to control body lean, etc.

Pretty impressive systems.

-Rod