Troubleshooting Wheel Speed Sensors

I have a 2008 Silverado that I'm 99% sure has a wheel speed sensor that has failed leadingto the ABS and traction control not working. I want to fix this. I could just bring it to a dealer and they could use the special computer to ask the ABS computer what's wrong but I object to this on monetary and philosophical grounds. I want to do it myself. The sensors are about $100 each on rock auto. Is there away short of buying one and swapping it out until I figure out which one was the bad one to fix this? Is there a way to test wheel speed sensors to see if they work?

Do you have an oscilloscope? Most of them put out a sine wave, with both the voltage and frequency increasing with speed.

My car does the same thing. Replacing the sensor didnt help, seems like the issue is with the ABS module.

My Malibu had a speed sensor code, one of the connectors has a bit of corrosion in it after the winter. A bit of cleaning with a small wire brush and some dielectric grease fixed it right up.

It can be as simple as debris on the magnetic part of the sensor, I'd do a quick visual inspection / cleaning of the actual sensor bits and electrical connections before throwing parts at it.

Just pulled the first front sensor and cleaned it and polished the electrical bits with the dremel and put it back together. It requires removing the caliper and disk to get it out. I'll do the other one this afternoon and then get the rears which are a bunch easier.
This makes me want an oscilloscope.

The easy button is drive to autozone and see which code popped before starting "work" diag. The hard way would be trying to figure out which sensor is the issue by testing ALL of them and comparing differences. You should be able to find the bad one with a basic multimeter, assuming it's actually a sensor problem. I would definitely start with a visual inspection of the sensor/tone-ring interface followed by the sensor connectors. Hopefully it's not one of the internal tone rings you cant actually look at without taking the sensor out. Cant remember offhand.

On your truck each sensor has two terminals at the connector. On the vehicle side of the harness, the fronts will have a grey wire with white tracer which should be 12v reference. On the rears they will be grey with black tracer as the 12v reference. The signal wire is colored differently for each wheel but it's always the other one so you should be able to test for power to the sensor, and then with some careful backprobing (bust out the safety pins!) able to detect activity on the other line with the wheel spinning. It will be hard to tell how consistent the signal is without a scope, but the meter will tell you whether you have power to the sensor and whether or not the sensor itself is completely dead.

The tone rings are inside the front hubs/rear axle tubes. I'm starting to think I should direct all questions directly to Vigo.
Thanks for the advice. I'll see what I can track down.

I just went cruising through alldata looking for relevant info. That's one of the benefits of working for places that use it. On my personal cars i usually buy a yearly subscription to alldatadiy for ~$15-18 depending on coupon codes. It's good stuff!

If it is electrical it needs voltage to run, so make sure that the senosrs are supplied with power.

If it does anything, it will have an impedance (resistance) so get the ohm meter out and make sure they are all the same.

If you have an analog voltage meter, you might be able to observe a signal out. You are only looking for one that is different than the others.

Failed or rust buildup changing the gap clearance? Does it so the under 5mph no stop deal?

That is a lot of work!!!!

Try the EZ stuff first.

Jack it up and find which of the front wheels, has a bad bearing replace bearing.

Bearings are good. They don't wobble and they spin smooth like butter anyway. All of them are de-gunked. The fronts looked good, the rears were decidedly corrisionany. I'll let it run a few key cycles/trips to school and see if it thinks it can see stuff again. I did take the opportunity to show my 10 year old all of the parts of a disk brake system. Good bonding and got him out of his mother's hair for 15 minutes.
Next is voltage checking and then I'll break down and bring it to someone with the proper computer.

Does this truck have the front hub-bearing assembly with the sensor built in? If so it could be an early sign of bearing failure. I've replaced more than a few hub-bearings on late nineties GM trucks, I'm pretty sure that all of them were giving ABS codes before they failed.

All of them over 100k miles, if it matters.

My money is on the front bearings. You can use my reader for $130 deposit including shipping. Or you can keep it

It has the hub bearing with the ring built in, is that what you mean? Over 100k miles. The truck has had an intermittent ABS light since it had 10k miles on it and it started happening with some regularity this winter. Eventually I could predict that if it was below 30, I would be greeted with lights by the end of the driveway. Eventually the lights went on one cold morning and didn't go off. If it's a bearing and they both feel good, how do I figure out which one is going bad?
Or do I just replace them both?

Complete Timken hub assemblies with new sensors in them are $115 on Rock auto. That's probably the easy button.

You are on the money. If the bearing has any play in it it is bad. They tend to go out on GM trucks around 60k. If it has 20s on it all bets off.

I agree with pretty much everything in this thread so far, but I would like to clarify a couple things. There are two types of WSS out there and the operational characteristics are a little different for each. I don't recall off the top of my head what your vehicle is equipped with, but here is the nitty gritty of the differences between the sensors.

Passive WSS

• They do not have 12V supplied to them.

• They will read OL if checking resistance with a DVOM (wheel/hub not spinning).

• They will generate AC voltage if you back probe with a DVOM and spin the wheel/hub by hand.

• They produce a sine wave on an oscilloscope.

Active/Hall effect WSS

• They do have 12V supplied.

• They will show some resistance on a DVOM (wheel/hub not spinning).

• They do not generate AC voltage.

• They produce a digital/square wave pattern on an oscilloscope.

If you do go shopping for oscilloscopes, give the PicoScope a serious look. They're pretty neat and darn handy for all sorts of electrical diagnosis.

Definitely need an o-scope to troubleshoot it.

Love my Snap On LS2000

What fixed it?

You don't "definitely" need an oscilloscope to diag the sensors. It's not even the easiest option! That would be reading the wheel speed in datastream on an obd2 tool.

If your meter will read voltage, resistance, frequency and AC voltage you can do a pretty thorough test on both types or sensors. Even if your meter will only do DC voltage, AC voltage, and resistance (which is pretty much every meter in existence) you can still do worthwhile testing.

The question is really, at what point is it easier to buy a $10 bluetooth obd2 adapter and load some free or near-free scanner software onto your smarthphone so you dont have to do things the hard way?

Because oscilloscopes are fun and everyone needs several, at least one of them and old CRO. For car usage, I would say something like the Pico would be ideal, but I wouldn't want one on my bench as my only 'scope.

But yeah, pick up a cheap OBDII bluetooth adapter and download Torque. If you have an iPhone, throw it away, buy an Android phone, and download Torque. Mine has helped me solve so many issues with more cars than I can count. They're so helpful and CHEAP that there should be one in every OBDII car.