I've experienced the same thing with my Malibu Hybrid. The pedal returns to normal as the car starts, even if I'm running on the drive battery and the engine is off. The hard pedal behavior only seems to occur if I've pressed the pedal when the car is off.

 

I have yet to notice any of the symptoms you’ve experienced. The brake pedal is always fairly light until it’s pumped and.

 

My Gen7 will retain its vacuum overnight and even over a weekend. It has 113,000 miles and counting. You might want to speak with your service department about it.

 

I notice this with my 2015 SS sedan and it may be a leak in the brake booster...but mine's only done this when starting the car and only on occasion...

Bill

 

Same here. I just assumed the big brembos are too demanding when the car's off.

 

Feedback on this one seems pretty mixed. I am going agree with DrivenDaily on this one; you might mention what you experience to your dealer and just get their opinion. As for my own experience, my LT pedal has never been difficult to press when starting the car. Nor has any other gen9 1.5T I have been in. Of course if you pump it while off it may be normal but if you just park get out get in and it is "very difficult" to push I would find that abnormal considering the others I have been in.

 

Been feeling that on all my vehicles. My '16 Malibu, my wife's brand new '17 Golf Alltrak, my '06 Avalanche and my wife's long departed '05 Vue.


Sent from my iPhone using Tapatalk

 

Hard brake pedal on my new 2017 Malibu as well. You can feel the pedal go down as soon as the engine starts. I'm not worried about it.

 

The brake booster is not keeping the vacuum reserve, it's NOT normal. I've gone over a week with not driving any car I've ever owned, new and old (this includes the current cars in my household, a 2017 Premier, a 2010 Equinox and a 2005 Mazda3) and the reserve is held when I depress the brake before cold crank, I've never had it bleed off just sitting for days at at time much less overnight. This sounds like a vacuum leak in the system. Now, if you press the brake pedal a couple of times when the engine is off the vacuum will bleed off, in the cars I've owned usually on the 3rd press you feel the vacuum assist has bled off some while the engine is off.

This is not a new brake system design in these cars, the same basic vacuum assisted brake systems have been used in cars since at least the 1960s (some earlier). If your pedal is hard before crank AND the pedal wasn't pressed after the engine was cut off AND it's only been overnight get it serviced, something is wrong.

 

Thanks all for your replies; I will do a little testing to see how long it takes before the vacuum boost goes away. I started it this morning, shut it off, and waited about 15 minutes; it worked fine only being off for that amount of time. I know that overnight it will loose its assist, and requires a restart to bring back. It should have braking ability as mentioned, for a few applications of the brake pedal, with the engine off. I did shut off the engine, then applied the brake about 4 times before the pedal got hard to depress. It has to have a slow leak somewhere; now to find a service tech that will understand and be able to resolve this.

 

How many miles on the car? With a 2017 I would think it's well within the warranty period.

 

The Malibu is virtually new; 287 miles. At my earliest opportunity I'll have it checked out. Until then, applying extra pressure to depress the brake pedal to start it is what I have to do.

 

There are 2 general types of brake assist: vacuum and hydraulic. I have seen some of the more expensive cars use hydraulic pressure from the power steering pump, but they have to use a small high-pressure tank to accumulate pressure for use if/when the engine is off. Those systems routinely get about 1 brake application without the engine spinning and then they become almost unmanageable. All of the vacuum systems I have ever seen have always used a large booster housing to store "vacuum" for use whether the brake is being applied while the engine has no manifold vacuum, such as during WOT (wide-open throttle) or after the engine has been turned off. With those I have always gotten 2 or 3 brake applications, and sometimes more.

If you park your car and remove your foot from the brake and then turn the car off, there should be vacuum left in the booster the next time you step on the brake, whether it's the next day, the next week, or even the next month.

If, however, you park your car and leave your foot on the brake, that action could be what is consuming the stored boost that should be available. Observe how you park your car and then see if changing how you do it leads to a difference the next time you start your car.

If you still have no boost left, or if it's still so minimal that it feels like there's nothing there, then get it into the dealer. There's a possibility that you have something wrong that could fail while you're driving it.

---

The term "vacuum" is actually a misnomer. It is actually a pressure difference. Outside the engine we live in an atmosphere with the pressure of (wait for it) ONE ATMOSPHERE, or 1 atm. When your engine is running and the throttle plate is not fully open the pressure inside the engine will be less than 1 atm.

As mentioned, a mercury barometer makes measurements in inches of Mercury (in Hg). Pounds per square inch (abbreviated as p.s.i.) is common in the English system of units, and the pascal (abbreviated Pa) is the standard in the Metric (SI) system. Since the pressure exerted by Earth's atmosphere is of great importance, pressure is sometimes expressed in terms of "atmospheres" (abbreviated atm). In weather, the bar and millibar (mb) describe pressure. You'll often hear millibar used by meteorologists when describing low or high pressure weather systems.

In summary, at sea level when it is 0ºC,
1 atmosphere = 29.92 in Hg = 14.7 psi = 101,325 Pa = 1,013.25 mb = 1.013 bar

Click here for website quoted above

The measurement we tend to see on our "vacuum" gauges is Inches of Hg with a second scale of mBar. — (Image) It is a measurement of the pressure below 1 atm and we, being humans, call it "vacuum".

Notice that the only place on the gauge that suggests that the vacuum is actually registering as a negative pressure is the minus sign before the "30". Also notice that the hand on the gauge rotates counter-clockwise, since that is in the direction of lower pressure. Higher pressure (aka, "less vacuum") makes the hand rotate clockwise. ("Clockwise" is assumed to mean "to the right" since this was written in North America where our clocks turn in the right-hand direction, as opposed to Germany where they turn in the left-hand direction. )

 

DrivenDaily, I keep my foot on the brake until after the engine is cut off. I never had any bleed-down of the vacuum reserve in any car I've owned or driven since 1978.

Granted I don't keep my foot on the brake long after I cut off the engine but the only time I had a problem was when there was something wrong with the braking system. And you are correct, it's a reduced pressure reserve, not a true vacuum but I'm using the term used in shop manuals and amongst repair professionals. I assume the system in the Malibu is not the hydraulic kind, especially since it uses electric steering.

 

You're 100% correct. If you press the pedal and keep your foot still it won't consume more of the vacuum to help you move the pedal.

There are other valves in the system aside from the one-way valve where the big vacuum hose attaches to the booster housing. One is between the brake pedal and the booster's vacuum compartment. Another is between the two sides of the booster. When the pedal is pressed, the last 2 valves are actuated. One seals off the 2 sides of the booster and the other allows atmospheric pressure to enter the driver's side. By increasing the pressure on the driver's side, the pressure differential helps apply the brakes. When the brake is released, the atmospheric valve closes and the 2 compartments are connected, which is what consumes ½ of the remaining vacuum.

I found some pictures on the internet that are not mine, but since they're out there I'm using them to help you guys understand how they work.

In the first one the green lines show where the air enters the compartment. The second is probably a professional drawing and just shows more mechanical details.

Click for video #1

Click for video #2

 

After the informative technical description of how the vacuum operated brake booster system functions; one can conclude that if there is no residual vacuum available in the brake booster, to allow the service brakes to function for a few applications without the engine running; there must be one or more components that are not sealing/holding vacuum, such as a check valve, valves within the booster assembly, or the booster housing itself. I believe we have narrowed the search where the problem exists. I guess if the dealer changes enough parts, I'm sure that this will be resolved. Again thanks to all who are participating in this discussion.

 

Let us know how it finally turns out and whether you get any pushback from your service professionals. You shouldn't, but sometimes humans will be humans.

You can tell from the participation that those who contribute thoughts or ask clarifying questions really have only one goal in mind: to arrive at a successful resolution to the issue presented. I really think that this is what prompted me to buy a used Gen7 after I lost my beautiful '11 LTZ to a flood. It's just odd that it was another '11 LTZ, with the same 3.6L V6 and the same color! (Not complaining!!!)

 

I have an appointment at my dealer Friday 9/8/2017 to attempt to diagnose and resolve this braking system issue. I will post my findings after this visit. I've found that remote starting is the way around the starting issue for now.

 

I've found that remote starting is the way around the starting issue for now.

You can't start?


Sent from my iPhone using Tapatalk

 

Well I just returned from my service appointment regarding my brake booster issue, here is the diagnosis:

"397 TEST THE BRAKE OPERATION
FOUND THE BRAKE BOOSTER IS LOSING RESERVE VACUUM
INSPECT FOR VACUUM LEAKS AND FOUND THE BRAKE BOOSTER TO BRAKE MASTER CYLINDER SEAL LEAKING
ORDERED PARTS FOR THE REPAIR"

The part ordered was a complete brake booster assembly.

When attempting to explain the symptoms to the service writer, and describing the apparent loss of vacuum in the booster, this is his response: "If there was no vacuum in the brake booster, the brake pedal would go to the floor."
My response to this was: "No, that isn't how it works, if it was a hydraulic system issue that may be the case." He then transferred me to a female advisor that actually listened to my explanation. Apparently she relayed the info sufficiently to the technician who then made the diagnosis.

I'll post after the repair to share the results.

Thanks to all who made comments, suggestions, and observations regarding this issue.

 

Glad it helped you understand your car better and hope it helped when you were there in the service department.

Let us know how it finally turns out. I'll bet starting the car will be more of a dream than a nightmare when it's done!

 

Update on the brake booster issue:

I had a new brake booster assembly installed, the brakes were bled, and the fuel trim was checked/reset. I went out the next morning after the repair and the problem has not changed. There is no vacuum in the booster reservoir after sitting overnight. I got a call from the dealer's customer service department to ask if everything was okay now; to which I responded that we haven't resolved the problem yet. I haven't scheduled a followup visit as of yet, as I was on vacation for a week, out of town. I'm not that concerned about the safety aspect, as the brakes work just fine, and after shutting the engine off, I have reserve vacuum available to operate the brakes with the engine off. It's only after sitting a number of hours or overnight that the problem exists.

If any of the Forum members here have the 1.5 turbo with the push button start; see if you are able to easily depress the brake pedal to facilitate a start, preferably after the engine hasn't been started numerous hours or overnight. (Mine is hard, cannot easily depress)

If I shut off the engine and immediately depress the pedal; I can depress it about 6 times before it gets firm/hard to depress, signifying depletion of residual reserve vacuum in the booster.

When attempting to depress the pedal after the vehicle has been off for numerous hours, the pedal is firm/hard on the first application of the brake. I cannot be made to believe that this is normal.

With a little feedback from some of you willing to see if yours operates the same way. Maybe I can determine what constitutes normal operation.

 

If any of the Forum members here have the 1.5 turbo with the push button start; see if you are able to easily depress the brake pedal to facilitate a start, preferably after the engine hasn't been started numerous hours or overnight. (Mine is hard, cannot easily depress)

If I park overnight the brake pedal remains easy to depress. If I leave it at an airport for 3 days it remains easy to depress. Of all the rental Malibus I have been in, all 1.5T cars, all have been easy to depress after being parked overnight.

With a little feedback from some of you willing to see if yours operates the same way. Maybe I can determine what constitutes normal operation.

I don't recommend getting sidetracked into thinking what you are experiencing is normal; Your dealer already diagnosed it as not normal. In my experience the loss of reserve vacuum overnight is not normal. The trick is figuring out where the issue is (see @DrivenDaily comments). I am curious, how is Hill-Start Assist working? If you stop on a moderate incline, let auto stop engage, then let off the brake do you stay stopped for at least two seconds before moving forward? No roll back?

 

With that new booster assembly, did it come with a new 1-way check valve and a new grommet? If not, that could be the whole issue.

Or not...

It sure sounds like there's just one little piece of this puzzle that's being overlooked, and it's probably been staring us all in the face the whole time!

 

I have the same exact thoughts. My service advisor claims that the assembly included everything including the check valve, but I have my doubts. I marked the booster before hand; it has been replaced, everything else, I have no clue. The valve and grommet to me were the first things I would suspect.

 

I think there is an electric vacuum pump somewhere under the hood to provide vacuum for the brakes during periods when there is no intake manifold vacuum. Maybe that's not working. Just a guess from the internet.

 

My Malibu is vacationing at my dealership while the technician is trying to determine why, after replacing the brake booster assembly, check valve, and tubing; there still is a loss of residual vacuum in the brake booster. The latest attempt to resolve this was to inspect/replace the o-ring seal between the master cylinder and brake booster. He's used a smoke/leak detector for diagnostic purposes, but still there is a loss of vacuum when sitting idle for a few hours. I was notified Friday that they were getting GM tech support involved on Monday. Meanwhile I was given a new 2018 2.0 turbo Equinox LT as a loaner. (The 2.0 turbo makes the E-Nox come alive; I can imagine how potent it is in the Malibu Premier)

 

I was notified Friday that they were getting GM tech support involved on Monday.

That should really help. Let us know the outcome.

As for the Equinox, I had a 1.5T AWD version a couple weeks ago. Being 500 lbs heavier than the Malibu but only a few hp more didn't make for a robust experience. The vehicle itself seemed comfortable and it was a bit quieter than the Malibu. It is a pretty major change from the previous gen... it didn't feel like a truck and felt more like a wagon.

 

hope they get your issue resolved...on the Equinox...I have read great things about the new Equinox, especially with the 2.0T...please share that experience after your Malibu issues get settled...

Bill

 

Yes, I think the brake system on the Malibu is now functioning normally: Answering your request for my observations of the 2018 2.0 turbo LT AWD Equinox.

The loaner Equinox I had for 8 days was basically new, had about 1200 miles.
I have a 2016 3.6 LTZ AWD as a comparison
The 2018 is a entirely new platform, weighs 400 pounds less than the prior generation
I was impressed by the acceleration the 2.0 turbo provided, seems quicker than the 301 hp V6 in my 2016
The 9 speed trans upshifts seamlessly, a little harsh when downshifting while coming to a stop
You cannot fool the 2.0 stop/start to stay running at a stop by slowing gently - It stops when the vehicle stops
The controls are very similar to our Malibu's - Features, Apple Car Play & Android Auto
The cabin in the 2018 E-Nox is comfortable but I wouldn't say it is quiet
Handling is acceptable, but not impressive - The ride seems to be slightly harsher than the prior E-Nox
Auto climate control works well
I liked the ability to turn off the AWD - It also has a tow/haul switch
I missed the ability to move the rear seat 8" fore and aft. The 2018 is fixed.
The 2018 is physically smaller - I liked that the prior model was slightly larger

Overall the 2018 E-Nox is a desirable crossover, although personally I still prefer the prior model, mainly because of the available V6, a little quieter cabin, a smoother ride quality, movable rear seat, and physically larger size.
The most impressive attribute is the thrust the 2.0 turbo provides.

 

I'm curious as to what the resolution to this is going to be. I've had my 2017 Malibu LT since Dec '16. Not quite 10k on it yet, and this issue just started for me about 2 weeks ago. Didn't think much about it and finally decided to check here to see if others were experiencing the same. I've also started noticing that after I've started the car, there is a traffic light shortly I usually stop at. The car seems to 'choke' a little while stopped (provided the auto stop hasn't engaged), as if it wants to go or is having trouble maintaining idle. It's not racing or anything, but enough to notice that it's not smooth. Wonder if this also has something to do with the brake booster. Guess I have a stop at the dealership coming up this week.

 

Well, I just picked up the Malibu yesterday after it spending 8 days at the dealership service dept. I was assured that it is now repaired. Here is the condensed version:
1 A brake booster kit was installed last month - reserve booster vacuum lost overnight - no improvement
2 Vacuum gauge leak test performed - check valve/vacuum sensor won't hold vacuum - replace part - still lost vacuum
3 Like vehicles in inventory tested - they hold residual vacuum
4 Contacted T.A.C. through dealer case management website - No bulletins or P.I.'s
5 Tested mechanical vacuum pump - only pulled 18 in/hg vacuum; spec calls for 27 in/hg - replace pump assembly
6 Leak test system using smoke test equip and soap solution - leak found at o-ring seal - master cylinder to booster
7 Replace o-ring seal, adding sealer to mating surfaces
8 Perform leak tests again - no leakage found
9 Bleed brakes - test for leaks again - let vehicle sit overnight - vacuum booster now retains residual stored vacuum
10 Vehicle now repaired

I have to commend the tech for his persistence in resolving this issue for me. Too many times a tech or service advisor will use the "could not duplicate problem" rhetoric, and send the customer off.

I believe the root cause of the loss of vacuum was two-fold, one being the check valve/sensor in the vacuum line to the booster didn't hold vacuum, and secondly the o-ring seal between the master cylinder and the brake booster was insufficient to hold vacuum. The mechanical vacuum pump was a surprise piece of the puzzle, but I believe it was not directly related to the loss of residual vacuum in the brake booster. Its function is to supply vacuum when the engine is in turbo boost conditions, when there is no engine vacuum supplied.

Parts used:
1 84038602 booster kit
1 15787976 seal
1 19353126 fluid
1 12662789 vacuum pump

 

I had my 2017 LT at the Chevy dealer yesterday to repair the hard brake pedal during startup issue. They replaced the brake booster and vacuum pump. In fact they replaced the exact same four parts you showed above. This morning, after letting it sit overnight, I went out to start it and found no improvement in the hard brake pedal, but that went away as soon as I started it up, just like before. One thing that I did notice during the drive home yesterday was that the brake pedal is much softer when stopping now. That does feel more normal, because before the pedal was pretty hard during stop and sort of felt like it had no pedal travel.

Oh well. I'll just drive it like this. It doesn't seem to be causing any problem anyway.

 

Thanks for updating the thread. I would make sure to ask for that same mechanic all the time. I might even have a pizza delivered to him at lunch time.

 

excellent review...thanks for taking the time and sharing your thoughts...

Bill

 

GarBec...that is exactly the reason I asked for your opinion...I get Car and Driver and had read that it was really something (or at least had that potential) but when I watched the Motorweek report you cited above (the cars.com version) they had a differing view...your review seems similar to the Motorweek/Cars.com review...that's disappointing to me.

Were I in the market, I would take one for a test of my own but I thank you again for taking the time and sharing your review...

Bill