ABS engages at low speed, sensors replaced, what to try next?

[bmishoe]

2003 GMC Yukon XL 1500, 2WD.

6 weeks ago or so, I noticed the pedal going soft and pulsating occasionally when I was slowing down with the wheels turned sharply (i.e. when pulling into a parking spot). It wasn't every single time, but often. I replaced both front ABS wheel speed sensors. The situation has improved (doesn't happen as often), but is still present.

Notes/questions:
1. on the drivers' side, I found 2 very thin shims under the factory wheel speed sensor; these were not present on the passenger side. Is this thing so sensitive that a couple thousandths shim would make a difference? That's hard for me to believe.
2. I noticed my passenger side spindle+bearing was loose...I'm going to replace that but wondered if the movement there could play a role (since it would move the teeth inside the bearing farther/closer to the sensor)
3. I haven't checked the rear sensors yet...is there a way for me to isolate which wheel(s) the ECM thinks are locked up?

 

[TollKeeper]

This is a tough one to diagnose without a high end scanner. You have to plug a scanner in, and look at the wheel speeds of each wheel. You will likely see one drop out. Thats going to be the bad one. I had this issue on my GMC. For me it was the right front wheel speed sensor. Replaced the hub/sensor. Problem went away.

Yes, a bad wheel bearing can cause this, but usually it either works, or causes a complete failure.

 

[Joseph Garcia]

A Tech 2 will identify specific problems, including which wheel is causing the problem.

 

[MassHoe04]

Unless you were getting ABS lights or codes, I kind of have a feeling your issue is not ABS or speed sensor related.

In terms of your shim question on the sensors, try this:

Remove the sensor on the side with the shims.
Remove the shims.
Place the sensor in the hole and leave the bolt out.
Place a finger on top of the sensor and gently feel for any vibration or movement when you turn the hub slowly by hand...,

If you feel anything at all, that would mean the sensor tip is making physical contact with the ribs of the reluctor ring inside the hub.

If that happens, add one shim and try again.
If you don't feel anything now, with the one shim, then the sensor is not touching the ring inside the hub and should still be close enough to pick up signal from the ring.
If you still feel something making contact, add the second shim and see if that gets it off of the ring for you.

A Tech 2 would allow you to look at what the signals are sending to the control modules.

But whether or not your sensor needs any shims or not depends on the sensor. Going by feel to see if a shim is needed is not hard.

I have replaced hubs, which came with new sensors specifically paired for the hubs. But prior to that, I was getting ABS lights. Replaced the sensor. The old one had shims. The new one needed no shims.
The hub failed shortly after, so that is when I replaced with complete hub/sensor replacement part.

 

[MassHoe04]

Just noticed question #2...

Absolutely! A failing hub can 100% cause the sensor to misread or not read at all sometimes. ABS speed sensor codes can definitely be the canary in the coal mine. Ask me how I know that one...
Never fail to investigate hub condition whenever ABS issues pop up. Besides. New hubs often come with matched sensors pre-installed. Plug and play and usually no issues with the matched sensors.

 

[TollKeeper]

Just noticed question #2...

Absolutely! A failing hub can 100% cause the sensor to misread or not read at all sometimes. ABS speed sensor codes can definitely be the canary in the coal mine. Ask me how I know that one...
Never fail to investigate hub condition whenever ABS issues pop up. Besides. New hubs often come with matched sensors pre-installed. Plug and play and usually no issues with the matched sensors.

As a rule of thumb, I never replace a ABS sensor if a new hub bearing comes with the sensor. Which generally speaking, they all do now.

 

[Sam Harris]

2003 GMC Yukon XL 1500, 2WD.

6 weeks ago or so, I noticed the pedal going soft and pulsating occasionally when I was slowing down with the wheels turned sharply (i.e. when pulling into a parking spot). It wasn't every single time, but often. I replaced both front ABS wheel speed sensors. The situation has improved (doesn't happen as often), but is still present.

Notes/questions:
1. on the drivers' side, I found 2 very thin shims under the factory wheel speed sensor; these were not present on the passenger side. Is this thing so sensitive that a couple thousandths shim would make a difference? That's hard for me to believe.
2. I noticed my passenger side spindle+bearing was loose...I'm going to replace that but wondered if the movement there could play a role (since it would move the teeth inside the bearing farther/closer to the sensor)
3. I haven't checked the rear sensors yet...is there a way for me to isolate which wheel(s) the ECM thinks are locked up?

I’m confident that hub situation is contributing to your problem.

 

[MassHoe04]

I got the premium hubs from NAPA for the price of standard-grade hubs RockAuto had, when I happened to hit a 20% off discount code for NAPA online purchases. I did online purchase and picked up local (no shipping and in-stock same day).
That might have been just luck in hitting that, but it was a great price.

I got the SKP hubs with sensors pre-installed. I found out later SKP was Moog. Plug and play. Zero issues with sensors since I replaced the hubs with these.

I would not advocate going bargain hubs. How many times would you want to replace them anyway...? One and done with GM (which are likely to be higher $ - but can't go wrong choice), Moog or SKP as next best alternatives.

 

[Doubeleive]

I got the premium hubs from NAPA for the price of standard-grade hubs RockAuto had, when I happened to hit a 20% off discount code for NAPA online purchases. I did online purchase and picked up local (no shipping and in-stock same day).
That might have been just luck in hitting that, but it was a great price.

I got the SKP hubs with sensors pre-installed. I found out later SKP was Moog. Plug and play. Zero issues with sensors since I replaced the hubs with these.

I would not advocate going bargain hubs. How many times would you want to replace them anyway...? One and done with GM (which are likely to be higher $ - but can't go wrong choice), Moog or SKP as next best alternatives.

who told you that SKP is MOOG?, 2 completely different companies, SKP makes a lot of oem stuff including GM hubs, Moog not so much they primarily do aftermarket

 

[Doubeleive]

2003 GMC Yukon XL 1500, 2WD.

6 weeks ago or so, I noticed the pedal going soft and pulsating occasionally when I was slowing down with the wheels turned sharply (i.e. when pulling into a parking spot). It wasn't every single time, but often. I replaced both front ABS wheel speed sensors. The situation has improved (doesn't happen as often), but is still present.

Notes/questions:
1. on the drivers' side, I found 2 very thin shims under the factory wheel speed sensor; these were not present on the passenger side. Is this thing so sensitive that a couple thousandths shim would make a difference? That's hard for me to believe.
2. I noticed my passenger side spindle+bearing was loose...I'm going to replace that but wondered if the movement there could play a role (since it would move the teeth inside the bearing farther/closer to the sensor)
3. I haven't checked the rear sensors yet...is there a way for me to isolate which wheel(s) the ECM thinks are locked up?

you need the code it shows when the abs light is on to narrow it down