Wheel speed sensor erratic?

[Litsnsirn]

I have a 21 Yukon XL Denali. I’m getting a ESC warning lite coming up, and when I checked it, it seemed like the Driver side rear wheel speed sensor was bad, so I ordered the replacement harness with the sensors and replaced it. Sourcing that and replacing that was a real treat, none of the parts houses online seemed to have it and I had to go to the dealer parts counter, if I wanted it in a reasonable amount of time. When I cleared the codes, they came back…. So, I am looking for a suggestion in what to check before I try to take it to the dealer. Do I possibly need to do something to get it to learn the new sensor or am I barking up the wrong tree? The codes that are present are:

C0510-00 Left rear wheel speed sensor erratic
U0418-00 Invalid data received from brake system control module 1
P25A2-00 Brake system control module requested malfunction indicator lamp illumination

This made me think the sensor was bad, but after changing it, no change in codes was present. Does the ring in the hub go bad?

 

[Fless]

Post your year, make, model and engine info, please, so we know what you're working on and can be sure your post is in the correct section.

 

[Litsnsirn]

Post your year, make, model and engine info, please, so we know what you're working on and can be sure your post is in the correct section.

Sorry, I forgot that, thanks! Edited the post with the correction.

 

[jfoj]

I would pull the connector that connects to the ABS module and check for moisture or corrosion. Then check resistance of each wheel sensor and compare them, they should be very close. If the Left Rear wheel sensor resistance is way off from the other sensors, unplug the wheel sensor and check the resistance of the wires to the wheel sensor, then each wire to ground.

Many years ago had a problem we were working on an ABS system that had a flakey wheel sensor reading, did pretty much the above, figured out the ABS wire from the wheel sensor had a trim screw compromise the insulation of one of the wires for the problem wheel sensor.

Good luck.

 

[Litsnsirn]

I switched over to my cheap Bluetooth code reader because the sensor outputs seem to be in a format that I can read and all four wheel speeds seem to be mostly the same.

 

[Fless]

The code means it's erratic, so you might have more success if you graphed them over some drive time and compared them to see if/when there are any discrepancies.

 

[jfoj]

The problem vehicle I was working on with a screw that damaged the insulation on a wheel speed sensor wire in the cabin near the ABS controller would only show up from a stop to about 3-5 MPH then the bad sensor speed would jump from 0 MPH then match the other wheel speed sensors once above say 5 MPH. The sensors would all track together once moving and above a threshold speed.

So perform the same test from a stop and watch the wheel speeds and also watch the wheel speeds as you come to a stop. One sensor may drop out prematurely.

What you may need and I am not sure your "cheap BT code reader" can support is to be able to graph 4 wheel sensors and take the vehicle on a drive. While there will be minor variations in sensor speeds when turning, you should be able to see a trend and any out of trend sensor behavior.

BTW, what BT scanner are you using that supports the wheel speed sensors? Yours clearly has extended support beyond generic OBDII.

 

[Litsnsirn]

This first one is an example of what the graph looks like on a good sensor:

 

[Litsnsirn]

Here’s the bad sensor:

 

[Litsnsirn]

Then a couple of minutes later, here’s the bad sensor again:

 

[Litsnsirn]

I’m kind of at a loss as to what I am looking at, not knowing the sampling rate, etc…

 

[jfoj]

I am guessing a bad connection or a wire that has rubbed to ground and is pulling the signal down. Since you replaced the sensor, it is not likely the sensor. I do not think the reluctor wheel could have drops like you are seeing.

Something more than likely damaged the wire for that wheel sensor somewhere along the harness?? Not sure if water or brake fluid could have made its way into the ABS controller, connector. I am not sure where it is even located in these vehicles, I am sure a Internet search or someone can tell us where the ABS module is located.

What I would do is jack up the drivers rear wheel and depending on the differential type, try and spin the wheel by hand and watch what happens. Sure it will be a slow speed, but you might have a helper pull on the wiring and bang around where you think the wiring harness may be routed while watching the sensor graph and see if you can force the drop outs.

Any history of accidents or flooding on this vehicle??

BTW, what phone App are you using that is showing the ABS sensor speed in a graphical format? BlueDriver? or something else?

 

[Litsnsirn]

Well, I have an update.

Dealer said that they think the hub is failing and generating debris, which is damaging the sensor. They want to replace the sensor i just changed and the hub. They gave me my car back while they order the parts.

 

[Fless]

I'm not too familiar with the physical layout of the sensor vs the tone ring, but it seems that the ring could be viewed with an endoscope through the sensor hole. Maybe I'm way off.

If what they say is true, isn't the "debris" going to trash the new sensor?

 

[Joseph Garcia]

Well, I have an update.

Dealer said that they think the hub is failing and generating debris, which is damaging the sensor. They want to replace the sensor i just changed and the hub. They gave me my car back while they order the parts.

That is what I was going to suggest. Loose debris bouncing around in the ring area could be temporarily sticking in certain grooves on the ring, thus distorting the signal generated, as the debris passes the sensor.

 

[jfoj]

I'm not thinking there is any debris on the reluctor wheel based on the drop outs, but I assume this would be a fairly easy check if you had a small borescope to put in the hole where the wheel sensor mounts and inspect the area while slowly turning the wheel.

It might be worth unplugging the wheel sensor and driving the vehicle while graphing the sensor. It does not cost anything to at least try and see what happens other than a little bit of fuel. In theory there should be no signal, but if the wiring is compromised without the sensor loading the wiring, you might see some spikes and strange behavior that would lead to inspecting the wiring and the connector at the ABS controller.

Not saying it will yield any specific results, but it is easy enough to unplug the sensor and try testing this theory. Depending on what you find, you can unplug the other rear wheel sensor and compare the behaviors of a good sensor circuit vs. the intermittent sensor circuit.