Intermittent ABS light issue

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greg716

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2001 Tahoe with almost 200k. When I bought the truck last October, all the brake lines were leaking. We replaced them all, bled brakes, etc. and reservoir has been holding fluid level fine. BUT- prior to yesterday, toward the end of nearly every stop the brake pedal would pulse like the ABS system was activating. Wet pavement, dry pavement, snow/slush/ice, no matter. Prior to yesterday, the yellow ABS light never came on. Yesterday, the yellow ABS light has started coming on and off intermittently. When it's ON, the brakes work just fine coming to a stop and there is no pulsing from the ABS system. When the yellow ABS light is OFF, it behaves as it has for the last 5 months with pulsing pedal, etc. There are no other lights on the dash at all, not the red BRAKE, no CEL, nothing.

I have a cheap code scanner that doesn't pull ABS/airbag codes, so I cannot say if there are any codes stored or not. I plan to go to O'Reilly's in the morning and have them scan, I'm posting this at work tonight because work is very slow.

Yesterday, I did install a new stereo head unit and front door speakers, but I cannot for the life of me think that would've had anything to do with it. I did not disconnect the negative terminal or pull any fuses as part of the head unit install.

Any ideas what might be happening?
 

MassHoe04

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I had ABS light that would remain off until I got to highway speed. Then, the light would flash and the chimes would start pining at me. When I got below 50 MPH, light went off and no more chimes.

I was not having pedal pulse or ABS activation. Mine was the opposite. It was warning me that ABS was deactivated.

My issue was a a failing hub.

Your issue could very well be sensor issues.
Anytime the system detects differences in wheel speeds, the ABS should be activating.You could have one sensor sending wrong speed data (or no data at all).
But sensor speed data also requires the reluctor ring inside the hub to be the right distance from the sensor consistently in order to work right.
You could have one or more hubs with excess play from being worn out over 200k miles. Excess play can mess with accuracy of the speed data sent out by the sensors.

Jack it up and check hubs for any grinding/rubbing/scraping noise, feel for binding or excess drag on the wheel, grab the tire and try rocking the wheel up/down and side to side.
You are looking for excess play or wear on the hubs.

You'll want to pull your sensors to inspect them to make sure they are not destroyed or covered in sludge or metal shavings.

If original, your hubs could be on the way out. They are about due for replacement soon anyway.

Most new hubs come with matched sensors.

Mid-range Zurich scan tools from Harbor Freight can be had for less than $150 that can read ABS and airbag codes.

Tech 2 clone scan tool will allow you to get deep into the system for about $300. Tech 2 can show live data from each speed sensor as you drive and store as as a snapshot to look at when done with the test drive.
You can see a graph of speeds from each sensor. Any one that looks different would lead to the sensor or hub that should be suspect. $300 is not small change to me, but was a worthwhile investment to diagnose and program stuff on my Tahoe, which has already saved me from having a shop make two repairs already. I was able to diagnose and repair both times as DIY. I easily got my $300 back already!

If I had to bet... I would really look hard at hub condition and the real possibility that one (hub with sensor) might need replacement now and the other soon after.
 
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greg716

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I had ABS light that would remain off until I got to highway speed. Then, the light would flash and the chimes would start pining at me. When I got below 50 MPH, light went off and no more chimes.

I was not having pedal pulse or ABS activation. Mine was the opposite. It was warning me that ABS was deactivated.

My issue was a a failing hub.

Your issue could very well be sensor issues.
Anytime the system detects differences in wheel speeds, the ABS should be activating.You could have one sensor sending wrong speed data (or no data at all).
But sensor speed data also requires the reluctor ring inside the hub to be the right distance from the sensor consistently in order to work right.
You could have one or more hubs with excess play from being worn out over 200k miles. Excess play can mess with accuracy of the speed data sent out by the sensors.

Jack it up and check hubs for any grinding/rubbing/scraping noise, feel for binding or excess drag on the wheel, grab the tire and try rocking the wheel up/down and side to side.
You are looking for excess play or wear on the hubs.

You'll want to pull your sensors to inspect them to make sure they are not destroyed or covered in sludge or metal shavings.

If original, your hubs could be on the way out. They are about due for replacement soon anyway.

Most new hubs come with matched sensors.

Mid-range Zurich scan tools from Harbor Freight can be had for less than $150 that can read ABS and airbag codes.

Tech 2 clone scan tool will allow you to get deep into the system for about $300. Tech 2 can show live data from each speed sensor as you drive and store as as a snapshot to look at when done with the test drive.
You can see a graph of speeds from each sensor. Any one that looks different would lead to the sensor or hub that should be suspect. $300 is not small change to me, but was a worthwhile investment to diagnose and program stuff on my Tahoe, which has already saved me from having a shop make two repairs already. I was able to diagnose and repair both times as DIY. I easily got my $300 back already!

If I had to bet... I would really look hard at hub condition and the real possibility that one (hub with sensor) might need replacement now and the other soon after.
Thanks for the response. I'm gonna look into that Tech 2 scan tool- I had something similar for my Ram and it was worth it's weight in gold- I didn't know Chevy had something like that (full disclosure, I haven't owned a Chevy for 15+ years).
 

rockola1971

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Thanks for the response. I'm gonna look into that Tech 2 scan tool- I had something similar for my Ram and it was worth it's weight in gold- I didn't know Chevy had something like that (full disclosure, I haven't owned a Chevy for 15+ years).
Just lift the front wheel(s) off the gorund just enough where you can freely turn them. Grab at 12 and 6 oclock and try to rock the tire inward/outward. If there is play in the hub you will feel it. A bad hub will cause the ABS to get bad readings from the wheel speed sensors and make it think you are losing traction on the front wheel(s) and actuate the ABS which is why you would be feeling the pedal pulse. When this happens you should be able to hear the ABS pump pulsing.
 

MassHoe04

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Just lift the front wheel(s) off the gorund just enough where you can freely turn them. Grab at 12 and 6 oclock and try to rock the tire inward/outward. If there is play in the hub you will feel it. A bad hub will cause the ABS to get bad readings from the wheel speed sensors and make it think you are losing traction on the front wheel(s) and actuate the ABS which is why you would be feeling the pedal pulse. When this happens you should be able to hear the ABS pump pulsing.
This^^^ costs nothing.

Not saying the scan tools are required to inspect hubs... Just additional tools that can usually help tell exactly what the ABS sensors are doing or confirm whether the computer is receiving the signals it should be receiving.

Here is what mine looked and sounded like just grabbing onto it and rocking it as @rockola1971 describes. I posted to YouTube

 

Joseph Garcia

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Lots of 'ifs' and 'maybes' here. Go to your local auto parts company who has scanner services, and get more insight on what is going on. Then, you'll be in a much better to zero in on the core issue and fix it in a least cost manner, without using the parts cannon.

I had a somewhat similar situation, and my Tech 2 told me exactly where the problem was.
 
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greg716

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Lots of 'ifs' and 'maybes' here. Go to your local auto parts company who has scanner services, and get more insight on what is going on. Then, you'll be in a much better to zero in on the core issue and fix it in a least cost manner, without using the parts cannon.

I had a somewhat similar situation, and my Tech 2 told me exactly where the problem was.
I did finally get around to doing this (was busy with work and a couple trips to the south from the frozen ******** of MN) and they didn't find any ABS codes... ugh...
 

Joseph Garcia

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I did finally get around to doing this (was busy with work and a couple trips to the south from the frozen ******** of MN) and they didn't find any ABS codes... ugh...
Did they find any other codes?
 

Doubeleive

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just a little bit of info
1. abs light on indicates a fail in the abs system so abs is disabled when the light is on, this is why you are able to stop without pulsing.
2. pulsing while coming to almost a complete stop indicates erratic abs data so it doesn't know what to do because it can't decipher the data so it does the best it can and "pulses" the abs pump.
usually the pulsing is caused by a bad abs sensor, but it could be one of the front hubs as well or even a bad sensor in the rear axle or bad connection.
the only way to really figure it out is by pulling the code while the abs light is illuminated. the code is not usually stored unless it is a permanent failure and cycling the key will erase it.
you can also look at the live data from the 4 sensors while driving and coming to a stop to see the erratic one.
if the abs light is on or comes on when you hit a bump or something then that points more to the abs module which can develop a loose solder connection from vibration over time, when this happens the abs light may come on while driving and go away when you shut it off and restart until it fails again when you hit a bump.
it could also be a combination of both a sensor and module given the mileage.
 

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