Strange intermittent ABS issue

[dal1980]

I have a 2014 Silverado Z71 CC and I'm having a sporadic ABS issue I need some insight on.  Every once in a while, so far when moving slowly, I will hit the brakes and the ABS kicks on and won't stop the truck.  If I let off the pedal and apply again it does the same thing.  It seems like two drive cycles will clear the glitch but its un-nerving to say the least.  The one time it happened while backing up with a trailer going down hill, not overloaded only about 4k total weight trailer and cargo.  Makes you pucker a little when you can't stop a truck and trailer combo going backwards.  Again, this has only happened at low speed but I'm starting to question how I would stop at higher speeds with or without a trailer?   The most recent brake recall from GM didn't include my VIN but I'm starting to think it should have.  So far all but one occurrence has happened on dry pavement in non-freezing Temps, so its not actually sliding.

[CamGTP]

To me that almost sounds like a failing wheel speed sensor. A sensor can drop out while the 3 others are reporting data to the computer still. The ABS will freak out and kinda what you are talking about.

 

This is just a guess at what is happening. Without a scan tool that can read ABS codes and watch each sensor function at the same time it's tough to really say what is the root cause.

[daveschevy]

It sounds like you are running out of vacuum. There is a extended warranty on the vacuum pump. Do this test, in a parking lot. At idle and in gear keep your foot on the brake pedal let the truck roll keeping a little pressure on the brake pedal see if you run out of vacuum and loose power brakes. I noticed it backing in my long driveway, by the end of my driveway I was out.  

[dal1980]

Good info, I'm heading in for state inspection in the next week or two, I'll have them look at the wheel speed sensors.  I'm going to try the vacuum test today after work.  Thanks for the replies.

[dal1980]

I dropped the truck of at the dealership and explained what was happening.  They are replacing the vacuum pump under warranty.  Per the recall, if your VIN doesn't fall in the recall category, then they extend your warranty to 10 years/150,000 miles on the vacuum pump and the brake booster.  SO, they don't want to recall all of the trucks, but will replace the parts IF you have the problem.  Thankfully, I didn't have the problem while launching my boat or the truck would've been in the drink.  While I understand the financial aspect of the selective recall, I don't understand it, in this instance given the nature of the failure.  I guess you could always grab the gain on your brake controller and use the trailer brakes to stop the truck, right?  Im sorry did you say surge brakes, oh too bad then, find something soft to run into.