2015 Suburban hard brake pedal. Almost crashed through a wall.

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jstatham

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Hello everyone. I am looking for some advice. I have a 2015 Suburbam 4x4 with 70k miles on it. I do all my own maintenance and car repairs but this one has me scratching my head. This weekend while pulling into a parking spot the brakes virtually failed. It took all I had to stand on them to get the suburban to stop. I almost plowed through a building. I then slowly went forward and backwards and it felt like I had old drum brakes. I then turned it off then back on and they started working fine and hasn't failed anymore. I did some googling and there was a TSB PIT5361C about additional brake pedal effort. This weekend I pulled the vacuum hose and it was clean on both ends. I also stuck a wire with a cotton ball and put it down in the brake booster and got no trace of leaking oil or brake fluid. I am not sure where to go next. Any help will be greatly appreciated. My wife is scared to drive it now. I also did some googling and several people have complained about the issue. http://m.carcomplaints.com/Chevrolet/Suburban/2015/brakes/service_brakes.shtml

I am not sure what to try next since all the diagnostics passed and I don't want to start replacing parts for no reason. What would you do? I have a buddy thats a GM mechanic and he is the one that told me what to test but its all good.
 

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a hard peddle as opposed to a pedal that goes to the floor is typically caused by a brake booster failure or a loss of vacuum to the booster.
did any warning lights come on?
do you ever notice a rough idle?
you checked all vacuum hoses for cracks or not fully attached?
are there any electrical connections to the vacuum pump that could have issues?
I assume the brake master cylinder is full.
 
zora said:
a hard peddle as opposed to a pedal that goes to the floor is typically caused by a brake booster failure or a loss of vacuum to the booster.
did any warning lights come on?
do you ever notice a rough idle?
you checked all vacuum hoses for cracks or not fully attached?
are there any electrical connections to the vacuum pump that could have issues?
I assume the brake master cylinder is full.
Click to expand...

It was definitely a hard petal. No warning lights and no loss of vacuum. There is a sensor on the booster vacuum line and it never kicked off an alarm. I completely removed the vacuum hose and checked for leaks and oil and it all checked out clean. Everything seemed OK and the master cylinder was between the min and the max. I marked it with a sharpie so i can tell if I have a leak. I am not sure what else to do.
 
is there a way you can test the sensor to make sure it is working?
apparently it is there to warn of a loss of vacuum so that eliminates the pump and points to the booster having a failure unrelated to vacuum,
 
I am not sure. I will research. I thought if the booster failed it would fail for good and not every now and then.
 
not a good way to approach it but if it happens again check if the AC controls work, they also depend on vacuum. There are 924 TSB's for the 2015 Suburban with about 20 on the brake system. Other than the problem with engine oil getting into the vacuum system I could not find anything related to a hard peddle.
 
Thanks. I am going to pull the master cylinder and physically look into the booster this weekend and see if I see a leak.
 
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