Hello all,

2001 YukonXL 4WD 5.3 Autoride 302,000 miles. ABS and BRAKE light come on occasionally under the following circumstances with no apparent rhyme or reason:

- During a long drive
- During a short drive
- On bumpy road
- On smooth road
- Moving
- Sitting still idling in gear
- Sitting still idling in Park
- Moving forward
- Moving backward
- Uphill
- Downhill
- Turning
- Driving straight
- In the sun
- In the rain
- Towing a trailer
- Using a hitch-mount cargo carrier
- Towing nothing
- Packed full
- Completely empty except driver
- Completely empty including driver (yes, lights came on idling and empty once. Was off, got out, walk up to car to get in and they are on already)
- Anywhere between sea level and 11,013 feet above sea level
- From 29 to 45 degrees North latitude
- From 94 to 119 degrees West longitude

Yes, really. I've been studying the issue for probably 40,000 miles. I know the list is a little out there. At least I'm thorough in my description.

I'd say 90% of the time it doesn't have this issue, the other 10% of the time it uses one of the above reasons, from a well-shuffled deck, to light ABS and BRAKE . Sometimes it does it when the car has been sitting all night, I get in, close the door, start the engine, let it idle for a minute while it cures its morning piston-slap issue, and it will light them up part way through idling. Sometimes does the same when warmed up. Last Saturday, after idling at a friend'* house for probably ten minutes, friend walked out with her kids and as they got within ten feet of the car the lights came on. Myself and all passengers in the car weren't moving, except for my kids playing on their tablets.

The issue hasn't gotten progressively worse over the 40,000 miles it has had it. It doesn't affect performance in any way including ABS. I've had the car for around 120,000 miles now.

Anyways, I've scoured the internet (including GMForum) for a solution and I've gone through cleaning all manner of ground points and checking ABS sensors etc. I even went back through and added anti-oxidation grease like we use in the radio-tower world for ground connections. Still have the issue. It has relatively new front wheel bearings that the issue has survived through.

My question: What part is sad when it illuminates these lights? As in:

- There is something telling these lights to illuminate, probably the PCM
- It has a good reason to do this, as in "if I see condition W I illuminate light X, and if I see condition Y I illuminate light Z" and perhaps it also has "if I see condition V I illuminate lights X and Z" and I know it has "if I illuminate lights X and Z I keep them illuminated until the end of time or until the engine is turned off, whichever comes first"
- Something gives it this/these reasons
- What is/are that/those thing(*)?
- Why is/are it/they sad?

I'd appreciate any help on this. I'm hoping someone who works a shop and fixed this for a bunch of demanding customers years ago has the answer. It'* a nuisance, but would like for it to go away, and maybe if we solve my problem for sure, we will have solved the issue for many others who are still searching.

Thanks!

Do have have a reader capable of reading the stored ABS+codes?
Sure would be nice to read them, know what codes are responsible for when ABS/Brake-dash lights are on.
Any codes stored?

I wish. I'd love to know more of what goes on in its mind.

My reader (Bluetooth ELM327 + TorqueOBD2) doesn't show any codes, but it only reader P codes as far as I know.

Have you tried unplugging the brake fluid level sensor to see if it quits doing it?

That'* all I got

The obvious starting point is reading what code is stored.....

Seen intermittent ABS lights caused by rust buildup under the front sensors...

Do you know anyone with a shop scanner?
What kind of scanner is Autozone loaning out now a days?
If not, probably best to find a capable shop, for a minimal fee.
Talking about under, I want this under the tree next X-Mas!

That one above, only $4000.
https://store.snapon.com/SOLUS-Ultra...l-P651353.aspx

Autozone uses the cheap Actron scanners that only scan for P-codes.

Best bet would be to head up the dealer, pay the 1 hour diagnostic time and have them print out all the codes. As long as you are willing to pay the diag time, they shouldn't be reluctant to give you the codes.

An hour to just read ABS codes?

Good idea, I hadn't thought of that. I'll try it (right after checking the brake fluid level).

The front sensors are the ones that are built into the wheel bearings, right?

If so, they've been replaced after the issue started, with no change to the behavior of the lights.