"Service Brake Assist" message as well as weird anti-lock brake issue

[Cryptothedog]

So I having a couple of odd braking issues. This weekend I was braking hard to avoid sliding down a steep snow covered road. My Anti-lock brakes kicked on but I was not able to actually stop. I ended up putting the ebrake on and that was able to stop me. While braking I got a message that said "service Brake Assist". I have seen this issue one other time a few months ago and while backing in my camp trailer. That time it felt like I had no brakes at all. I read that this may be the vaccuum pump but I am also having this really odd issue that I have actually had for a couple of years now where if I back up or go forward and then quickly brake shortly after moving (even on dry pavement) it feels like my anti-lock brakes activate for maybe one second. It only does it at slow speeds like right after backing out of a parking spot or something. That didn't seem to be mentioned in the service bulletin. So maybe it is a separate issue but maybe it is related, I don't know. Does anyone have any advice? Or should I just replace the vaccuum pump/hose and hope that fixes it?

 

[Doubeleive]

So I having a couple of odd breaking issues. This weekend I was braking hard to avoid sliding down a steep snow covered road. My Anti-lock brakes kicked on but I was not able to actually stop. I ended up putting the truck in reverse and that was able to stop me. While braking I got a message that said "service Brake Assist". I have seen this issue one other time a few months ago and while backing in my camp trailer. That time it felt like I had no brakes at all. I read that this may be the vaccuum pump but I am also having this really odd issue that I have actually had for a couple of years now where if I back up or go forward and then quickly brake shortly after moving (even on dry pavement) it feels like my anti-lock brakes activate for maybe one second. It only does it at slow speeds like right after backing out of a parking spot or something. That didn't seem to be mentioned in the service bulletin. So maybe it is a separate issue but maybe it is related, I don't know. Does anyone have any advice? Or should I just replace the vaccuum pump/hose and hope that fixes it?

has the recall been performed?

https://static.nhtsa.gov/odi/tsbs/2019/MC-10167479-9999.pdf

 

[Cryptothedog]

has the recall been performed?

https://static.nhtsa.gov/odi/tsbs/2019/MC-10167479-9999.pdf

I'm not sure but I'm past the 150,000 mile limit that it references and its a 2015 so also past the age limit. So it looks like I need to replace the pump and belt. Would that cause my Anti-lock brake issue too?

 

[Doubeleive]

I'm not sure but I'm past the 150,000 mile limit that it references and its a 2015 so also past the age limit. So it looks like I need to replace the pump and belt. Would that cause my Anti-lock brake issue too?

I would recommend using a decent scanner that can read the specific error codes and see what crops up (if anything) and go from there.
otherwise your shooting in the dark with the parts cannon. could be a hub causing abs sensor issue's, the brake module, or a pinched wire harness, etc

 

[Doubeleive]

as for the TSB if the software ntsb recall has not been done that never ends...
you can call or go by any gm dealer, provide your vin number and see if it is in the recall

 

[Cryptothedog]

Gotcha. Any advice on a good scanner that isn't too expensive? I just have a cheap harbor freight bluetooth one that only reads codes but I dont think it will do diagnostic info

 

[Cryptothedog]

Gotcha, ok I'll call the GM dealer and see. Thanks for the info!

 

[Cryptothedog]

as for the TSB if the software ntsb recall has not been done that never ends...
you can call or go by any gm dealer, provide your vin number and see if it is in the recall

Called the dealer, looks like it was done 4 days before I bought the truck back in 2022. So they last about 70k miles it looks like lol so I'm on my own with that. I'll look into the scanner. Thanks.

 

[Chris Mosher]

It’s definitely the vacuum pump. I just replaced mine and put on a new belt. Problem went away instantly. The loss of brake power in reverse and while in traffic/parking lots is from no vacuum assist.

 

[Cryptothedog]

Awesome, thanks for the advice everyone. I’ll be replacing that pump soon. Looks like a PITA to get to but I’ll make it work

 

[Fless]

Please come back and let us know if that corrected the problem.