2015 Tahoe LTZ - intermittent brake assist loss at low revs - vacuum pump??

[2015LTZ]

there is another known issue of the vacuum pump seal going bad and allowing oil into the brake booster that can cause a problem and yet another issue where the booster seal can leak
there is a service bulletin for the booster leak

https://static.nhtsa.gov/odi/tsbs/2016/SB-10081053-2280.pdf

there is a 10 year special coverage on the vacuum pump "if" IT fails diagnostics and or throws a "service brake assist" in the dic therefore setting a code.
https://static.nhtsa.gov/odi/tsbs/2019/MC-10167479-9999.pdf
I would pull the vacuum line off and check if there is fluid inside or if it is dry

If the vacuum pump fails diagnostics it's free under the special coverage for 2015-2018 for 10 years

Checked the lines, no fluid. Also fluid inside the booster is clear, no oil there.

 

[Ibustbravo]

Yea there's a vacuum pump on the right side of the engine. It's a real pain in the butt. When I rebuilt my engine I plugged the holes in the block; for a future turbo install, and routed the line from the brake booster into the intake manifold. Pretty easy fix. I guess you can call that a 'vacuum pump delete'

 

[Doubeleive]

Checked the lines, no fluid. Also fluid inside the booster is clear, no oil there.

I re-read your original post, you might want to check your front hubs. if a hub or "hubs" are wearing out this can cause both your noted symptoms and the noise (noise while wheel is spinning anyway)
jack up the front so the wheels are off the ground and see if the wheel has any play at 12 & 6 it should have none, you can also check 3 & 9 but there will be a little normal play there because of steering, you can also spin the wheel and listen for any noise, should be pretty much silent.
a vacuum pump issue would be pretty unlikely to cause a abs activation, but a lazy abs wheel sensor would and that normally is because of hub wear but not 100% always a sensor can be bad as well but is less likely.

 

[OR VietVet]

I gotta wonder why they need a vacuum pump on a stock engine, for brake boost? Are they just adding to the inches of vacuum just to cover something?

 

[2015LTZ]

I re-read your original post, you might want to check your front hubs. if a hub or "hubs" are wearing out this can cause both your noted symptoms and the noise (noise while wheel is spinning anyway)
jack up the front so the wheels are off the ground and see if the wheel has any play at 12 & 6 it should have none, you can also check 3 & 9 but there will be a little normal play there because of steering, you can also spin the wheel and listen for any noise, should be pretty much silent.
a vacuum pump issue would be pretty unlikely to cause a abs activation, but a lazy abs wheel sensor would and that normally is because of hub wear but not 100% always a sensor can be bad as well but is less likely.

Thanks for this. Just wanted to know what are the symptoms of a faulty vacuum pump?

Also, the location of these abs sensors? How to check and replace

 

[Doubeleive]

Thanks for this. Just wanted to know what are the symptoms of a faulty vacuum pump?

Also, the location of these abs sensors? How to check and replace

the symptoms would be a loss of braking at low rpm or having to press the pedal harder than usual or even loss of power brakes period, or a "service ***" message in the cluster.
the abs engaging at low speed or just before coming to a complete stop would likely indicate one of the sensors is not reading the same as the rest so the brake module thinks a wheel is slipping so it engages the abs pump to attempt to stop the vehicle without skidding (even though you may be moving slowly). the result is pulsing of the brake pedal and loss of brake control for a moment and then a sudden complete stop (or any combination of), you may hear a weird noise associated with it as well which is the abs pump engaging.
as far as checking the abs sensors, if there is no code or abs light on then you need a scanner to see live data when this is happening, the scanner will show all 4 of abs wheel speed readings and one may show 0 and the other 3 4mph or something to that effect. sometimes when this happens it's not a enough of a error to throw a code or light up the abs light but still causes a driveability problem.
if it is a abs sensor it's usually a front one and those are located on the front wheel hubs, behind the brakes.
hence why it is wise to check the hubs because when the hubs wear out it causes the abs sensor to go goofy because the sensor inside the hub is affected by the hub bearing being worn out.
the wheel hub is what has the lug bolts and the bearing that lets the wheels spin, the abs sensor is in a hole in the back of the hub with a single bolt holding it in and a wire that snakes up the upper control arm and attaches to the vehicle harness.
the sensor is magnetic and reads a corresponding magnet inside the hub and when it spins this is how it determines the wheel speed
there really is nothing visual to check, if one was unplugged or something you would get a abs light. some people say they can get rusty and that might be a cause, but if you have rust inside the hub then it's probably time for new ones anyway because bearings and rust do not mix well