ABS Sensor Frequency Test

[kohlbear]

I removed, cleaned and checked each wheel sensor. Then I checked each one with an OHM meter. They all showed around 1000 OHM, give or take 50 OHM.

I have heard the system whine at start up, but then it sets itself and shows the dreaded ABS code at about 7 miles per hour. I have heard that 90% of the time, the problem is a wheel sensor and they could still be bad, but require a frequency test to determine which one is bad.

Does anyone know what equipment is required to do this? Can Auto Zone or someone do the test on each sensor.

I have an 87 and I was told it does not store codes.

 

[Magmotor]

Your ohm's are correct, a little low but within limits. The sensor's freq: can only be tested when the car is moving, 6-8 mph for the correct output. And that can only be tested with the proper chassey scanner that plugs into the wiring harness of the ABS system. When you hear the whinning noise it is the mod valve and the entire system being self tested: mod relay, solenoid valve, solenoid relay, brake diode, lateral acceleration switch, all speed sensors, pump relay, all voltage and logic states, stop haz fuse, brake fuse, gage fuse and fuseible links. Any one of these can set the ABS light on if certain criteria isn't met. This system is kinda like a "leave it alone and let an expert fix it system" ......I would call a dealer and ask if they had the proper scanner for the ABS and let them deal with it.......

 

[bradfordsvettes]

you need to scan for codes before chasing wheel speed sensors some dvom meters measure frequency but the scan tool is really the only way to go to trouble shoot the system steve

 

[jpanek]

Here's a few ideas to check:

Wiring all the way up to the ECM
Connector corrosion
Missing teeth on the rotating part

To do your own frequency check you can use an oscilloscope. Unplug the connector to each sensor, put the scope on, and spin the wheel by hand to see the waveform. Compare all 4 with each other and a bad one will stand out.

Not sure about the vette, but on some cars a wheel underinflated enough to have a significantly smaller diameter will set an ABS code.

 

[vettenick]

If you can get your hands on a scanner with ABS capability, you can go on a road test and observe the input from each wheel sensor.