# No Brake Assist in Reverse



## joekexel (May 17, 2017)

How to best test the electric vacuum pump? Specifically, what can I do to make sure that it will be turned on? At idle, no vacuum comes from it, but from what I hear that may be normal. Should I put in into reverse while I have the ignition on? Would that work? 

Second, if it is the vacuum switch at the end by the vacuum assist unit, what is that thing called? My Autozone couldn't find it. Seems like a GM specific part, part number anyone?

Thanks for any help.


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## joekexel (May 17, 2017)

joekexel said:


> How to best test the electric vacuum pump? Specifically, what can I do to make sure that it will be turned on? At idle, no vacuum comes from it, but from what I hear that may be normal. Should I put in into reverse while I have the ignition on? Would that work?
> 
> Second, if it is the vacuum switch at the end by the vacuum assist unit, what is that thing called? My Autozone couldn't find it. Seems like a GM specific part, part number anyone?
> 
> Thanks for any help.


Okay, I think that part near the vacuum unit is a "*Power Brake Booster Vacuum Sensor*". Is that likely to fail? My guess is it is a micro switch with a diaphragm that actuates at a specific pressure. I would expect that to be relatively robust, but I am sure a million cycles would come quickly. 

I still need a way to best test the pump.


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## Valpo Cruze (Feb 23, 2014)

If memory serves, there was a recall for some gen 1 cars. My 12 had the problem and it was exactly like the recall problem but my VIN was not included.

My work around was to shut the AC off to make the brake assist work. I never did fix it since I could work around it


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## Mr_Pat (Mar 7, 2021)

T fitting with a vacuum gauge maybe ?


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## joekexel (May 17, 2017)

joekexel said:


> How to best test the electric vacuum pump? Specifically, what can I do to make sure that it will be turned on? At idle, no vacuum comes from it, but from what I hear that may be normal. Should I put in into reverse while I have the ignition on? Would that work?
> 
> Second, if it is the vacuum switch at the end by the vacuum assist unit, what is that thing called? My Autozone couldn't find it. Seems like a GM specific part, part number anyone?
> 
> Thanks for any help.


*I figured it out.*

*Apparently, Fuse 16 is not just the AQS shutter motors, it must power whatever triggers the power brake vacuum motor. I was playing around with a GPS tracker and wanted an ignition signal to show whether or not the engine was on. I was trying to avoid air bags, the ignition and other critical systems. Well, I failed!

Fuse 16 is a critical system circuit. Simply, the add a circuit fuse thing I used did not do a good job and was loose. The original fuse made the motor come on. 

So, keep that in mind. On a 2012 Cruze LT and others of that generation, that fuse (#16) controls the power brake vacuum motor trigger circuit, though J-CASE Fuse 26 actually protects the motor itself. 

The other thing I learned is the vacuum pump is simply a motor with a fan on it. The inlet will show a vacuum when on. I expect a plastic blade that will probably never fail, so if it spins its good. 

It is easy to determine if, it is at least working. If it is not working, other factors may be in play. 

Go to your Cruze, turn the ignition on, but do not start the car. When you press the brake and release, the vacuum will be used up and the vacuum pump will turn on. It will be obvious with the motor not running. You will notice it will turn off quite quickly, until you press the brake again. This is probably testing both the motor and the vacuum switch by the power assist unit. This should be "Situation Normal". I would recommend you do it now, just so you know how it works. If the motor does not turn off, I guess that may be the vacuum switch is defective or a vacuum leak exists.

I have not identified the part that is at the assist unit. I'm pretty sure it is a vacuum sensor, but the ones I see online do not have 2 inlets. The one on my Cruze has one for the engine vacuum and one from the vacuum pump before it enters the power assist unit.*

*Hope this can help others. *


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## joekexel (May 17, 2017)

*If you can reach the vacuum pump connector, you could try to put power to it directly to test it. Some YouTubers show that off the vehicle, but that could be a pain in the ass. These motors are not in nice places, LOL. Probably for they are not highly likely to fail. It if spins up, you are probably good to go. I do not think a vacuum gauge would be necessary for a fan. I doubt a fan blade is going to completely disintegrate before a motor brush failure. *


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