ABS Speed Sensor/Wheel Vibration

Wondering...

Since we purchased this car the Air Bag light has been on and we've had a vibration from the brakes when braking over 45mph. Not sure if the two can be connected.

Could a bad speed sensor be the issue? I have read that if the sensor is bad it might register the wrong wheel speed to the ECU which in turn is interpreted as wheel slippage. This causes a slight pulse to the opposite wheel to slow it down and regain control. The effect may come off as a vibration when braking.

How can I diagnose the speed sensors? And if the OBDII scanner would work does anyone have any suggestions as to good or bad ones?

If the ABS light is on the ABS will not work. The vibration your are feeling at higher speeds is likely warped rotors.

An OBDII scan tool will only read engine codes. You will need an ABS scan tool or a higher end scan tool capable of reading ABS codes and data.

There are four wheel speed sensors and I would bet one of them is bad. Unfortunately they are part of the hub/bearing assemblies and it can get quite costly on guessing which one is the bad one.

What you can do is unplug each sensor and use a multi-meter set to A/C voltage to measure the voltage from each speed sensor as you turn the wheel by hand (voltage will increas the faster you spin the tire. You should see around a volt A/C at each sensor. If one of them is not the same as the other than you have found the bad one.

If they all read about the same than you will need to scan the ABS module for codes to get a better idea of what the problem is.

Hope that helped

I'm sorry..I have seemed to combine two separate problems. An Airbag light that requires some kind of new part and the vibration we get when using the brakes at 45mph and above.

I had read a post that someone found the vibration coming from his brakes was actually a faulty ABS Speed Sensor sending out the wrong wheel speed in effect causing the ABS to engage just enough to cause what would be discribed as a vibration rather than a pulsing. My guess due to the slower speed and less force applied to the brake pedal.

Thanks, for your input. It really feels like the vibration is coming from the front brakes. Is there a way to disable the ABS just long enough to take it out for a test drive and see if the vibration goes away?

I've seen on other post how they've told them to pull the abs fuse for what your asking but be careful that means you have no abs brakes and your brakes will work like the ones on the old cars before they had abs brakes. Fiserman

I've seen on other post how they've told them to pull the abs fuse for what your asking but be careful that means you have no abs brakes and your brakes will work like the ones on the old cars before they had abs brakes. Fiserman

Too funny. Grew up with those old cars. Man, how did we survive those days?

I'll give it a shot...for science.

Update...pulled the ABS fuse and the vibration has almost gone away. The remaining vibration is definately rotors. The question is...did the faulty ABS cause the rotors or pads to wear unevenly or did the calipers/pads/rotors cause the ABS sensor to go bad. My guess is the sensor went bad and has caused the pads to wear unevenly.

Now, I need to figure which one is bad. I know I can measure the output from each sensor to see if one is out of norm. But can I just unplug one sensor at a time with the ABS re-enabled to see if the vibration comes back or not?

Thanks

Make sure you check your wheel bearings on your hubs. Had one go bad on one of my gm trucks and it would set my abs light off. Doesn,t hurt to see if a bearing may have caused your problem to. I had a bad speed sensor go out on my other gm truck that showed up on low speed not high speed. At less than 8 miles an hour it showed up and noitced that when it did it would make my dash lights dim for just a second or two. First truck put in shop. Had to replace hub assembly cost 500.00 laber and all at a gm dealership. Second truck put in shop, wheel sensor bad had to replace it cost about 300.00.

Discovered the problem.

The steering rack has gone bad. Estimate is $1050 plus tax. The rack is so loose it allows the wheels to vibrate badly enough the roters warped and the ABS kicks in on the drivers front wheel. With a new rack and alignment the ABS should not be triggered. Good news, wheel sensors and ABS computer appear to be functioning properly.