When attempting to push button start our 2017 1.5 LT; I've noticed it is very difficult to depress the brake pedal while attempting to start the engine. It seems as though there is no residual vacuum in the brake booster to allow the pedal to be depressed easily. I'm wondering if others operate this way, or that I may have a leaking booster or faulty check valve allowing the vacuum to escape after turning off the engine. Typically the brake pedal can be depressed a couple of times with the engine off, and still have assist from the brake booster. My pedal doesn't depress at all without the engine running.
Hard Brake Pedal When Starting Engine
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GarBec
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Garbec - It's been almost 4 months since your last post. I'm wondering if there is a resolution to this yet. I don't know how long my '16 has been doing this because I almost always remote start to warm it up. I happen to get in this morning without a remote start and noticed the pedal was very hard to depress. It has only been sitting for less than 18 hours since last driven.
Thanks,
Jim
Thanks,
Jim
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Jim,
After numerous attempts to resolve this, numerous components changed, and the vehicle spending 8 days on one visit to the dealer; the problem persists.
I just had the first service performed a few days ago, and brought up the subject again: They believed it was fixed because I didn't return to complain again until now. They are reopening the case to investigate.
I thought I would wait awhile to see if any bulletins regarding this problem have been created. So far I've put this aside as it is more of an annoyance than a safety issue; but definitely should be resolved. I just was tired of my vehicle being used as a test mule.
My latest observation is how there is no free travel in the brake pedal prior to activating the brakes when driving; this makes me question if because of this, the linkage is partially pressing the valve within the booster and causing the vacuum to slowly bleed down within the booster when the vehicle is turned off.
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Your theory sounds very plausible!
It wouldn't surprise me if they found out that someone welded the attaching pin on the brake pedal arm just a leeeetle too close, or used a connecting rod that's a leeeetle too long, causing the whole shebang.
It wouldn't surprise me if they found out that someone welded the attaching pin on the brake pedal arm just a leeeetle too close, or used a connecting rod that's a leeeetle too long, causing the whole shebang.
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Thanks Garbec for the reply.
I've noticed another thing that is brake related. It may also be related to this issue. If I come to a normal coasting stop, the brake pedal is easily depressed. On the other hand, if I'm accelerating and I quickly take my foot off gas and apply the brakes, the pedal does not depress as easily, almost as if theres not enough vacuum available. I am definitely going to mention it on the next service visit.
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We're on the same page on this one; this is my theory also. I've replaced master cylinders on older vehicles in which the push rod was threaded and adjustable. I doubt if this is true on a Gen 9 Malibu though.
Every other component in the system has been replaced except the linkage and push rod.
All other vehicles I've owned/driven have had a small amount of pedal free play prior to the activation of the brakes.
Now to find a service professional willing to listen to this theory, and ambition enough to investigate and follow through.
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When mine was being diagnosed for the loss of vacuum, the tech was advised by GM TAC to test the engine driven vacuum pump.
Upon testing he discovered it did not meet specs as to the amount of vacuum available. That pump was then replaced because of this.
This really has no effect on the loss of stored vacuum, but could be responsible for the symptom you described on yours. The pump supplies vacuum to the system when the engine is in boost from the turbo. During deceleration and idle, there is sufficient engine vacuum available without assistance from the pump.
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Mine started doing this about 8 weeks ago of so. Everytime going to turn it on, the brake pedal will be hard until started up. Has anybody gotten a real solution to this? Is GM doing anything about this matter? My vehicle is a 2013 Malibu LTZ 2.0L with 59900 miles. Dealer came back with power brake booster but i declined. So im curious if anybody has gotten a real solution
You can also find some info in the following threads:
https://www.chevymalibuforum.com/forums/121-problems-service-issues-troubleshooting-generation-9/110433-brake-pedal-squeak.html
https://www.chevymalibuforum.com/forums/121-problems-service-issues-troubleshooting-generation-9/108298-brake-pedal-squeak-press-release.html
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244 Posts
I just picked up our Malibu yesterday from my dealer to fix a MIL code P2097, in which the ECM was updated and both O2 sensors replaced. I also brought up the unresolved problem with loss of residual brake booster vacuum. The answer I was given was that after 5 hours, there was still ample vacuum stored to depress the brake pedal to facilitate a start. Also the tech went to three other new Malibu's on the dealer's lot; apparently all of these had lost their stored vacuum and the brake pedal was hard to depress, just as ours was. The invoice stated that the brake operation was normal. I give up! I can live with this, but obviously it cannot be normal. Whatever happened to the Chevy Customer Service reps that used to monitor our Forum and offer to assist with unresolved problems?
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My thoughts exactly. I give up i have no warranty in my car so im not going to spend money if nothing as previous people have said worked. Ill learn to live with it but forsure Chevy should do something. I emailed a chevy rep from this forum got a reply and I responded and haven’t gotten a reply back.
About 2 years ago I contacted them, first by PM, then by email, and then via phone. I related how they seemed by many, including myself, to be ineffective. Their responses were canned and showed no real understanding of the actual issue presented, no evidence of any resolution seemed to be shared, and very few ever reported hearing back from them. I told them that their value and/or effectiveness was determined by what we could see, which was an inconsistent presence and boiler-plate "answers". I felt like what I received was more of the same, since nothing really changed.
Their last post was May 2, 2017 at 16:30... Feeling forgotten now?
All of those corporate based reps seem to just act as a go-between. GM insulates themselves with the independent dealer model. If the issue isn't potentially safety related GM holds very limited liability and acts accordingly. As for the reps here, that was likely a feedback initiative when the gen9 was new. As of now there really isn't a single pervasive issue that receives dozens or even half dozen reports on here. Maybe the shift to park issue but they have been aware for a long time.
The P2097 doesn't seem figured out. There is an ECM update but it is for improved diagnosis. Don't see many reports of it on here so probably isn't a huge sample.
As for the booster vacuum, that has always been confusing. There aren't many reports and the loss doesn't seem normal. Some users have it and can't get it fixed and try other cars and they are all firm. Mine doesn't loose vacuum before or after the booster and master were replaced for the squeak and it sits for days sometimes at the airport. I've never been in a Malibu with the rock hard pedal and I've been in dozens via loaners and rentals.
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Yep, something's not right.. You might first check for leaks in the vacuum hose to the booster...If not there, ask dealer to replace the brake booster...It can be changed without disconnecting any of the brake lines since there is flex hose connecting the master cylinder to the brakes lines going to the calipers.
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I agree, but all of the components have already been replaced; vacuum lines, booster check valve, booster assembly, master cylinder, O ring between master cylinder and booster. The tech also employed a smoke test device to assist in the diagnosis. All related components except the linkage that connects the pedal to the booster and the linkage between the master cylinder and the booster have been replaced with no change in the gradual loss of vacuum. I have a theory that the rod between the booster and master cylinder may be of incorrect length (too long) and partially actuating the valving within the booster without even depressing the pedal. Getting someone to explore this theory and even understand what I'm trying to explain has so far been impossible. As this issue doesn't affect the safe operation of the vehicle, and only is an inconvenience when attempting to start the engine, it isn't on anyone's high priority list to provide a resolution. Probably most owner/drivers wouldn't even be aware this is occurring, and just apply more pressure to the brake pedal to facilitate a start.
My guess is either 1) a batch defect 2) the systems aren't assembled properly and gets put back together the same wrong way using the original as a guide or 3) there is a another problem causing the issue. If it had something to do with design they all would lose vacuum and be firm when starting; it wouldn't just be a half dozen or maybe dozen reports out of the hundreds of gen9 owners frequenting the forum.
As a side note, I don't believe anyone has reported a code from this issue but there is a ECM update for Brake Assist Vaccuum Too Low. It is a diagnostic update so is just there to gather more data from those affected. The update did appear after the recall update and the P2097 diagnostic update.
12691160 New calibration with diagnostic enhancements for DTC P050F (Brake Assist Vacuum Too Low)
12687988 New calibration with diagnostic enhancements for DTC P2097 (Post Catalyst Fuel Trim System Too Rich Bank 1)
12684516 Recall update
Source: https://tis2web.service.gm.com/tis2web/
As a side note, I don't believe anyone has reported a code from this issue but there is a ECM update for Brake Assist Vaccuum Too Low. It is a diagnostic update so is just there to gather more data from those affected. The update did appear after the recall update and the P2097 diagnostic update.
12691160 New calibration with diagnostic enhancements for DTC P050F (Brake Assist Vacuum Too Low)
12687988 New calibration with diagnostic enhancements for DTC P2097 (Post Catalyst Fuel Trim System Too Rich Bank 1)
12684516 Recall update
Source: https://tis2web.service.gm.com/tis2web/
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I agree that the symptom seems to be loss of brake assist vacuum, but am not aware of anyone confirming that by testing with a vacuum gauge to see if the vacuum level does in fact go down over time when the vehicle is off. Who knows, something else could be causing this problem. I have seen weirder things.
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I understand your skepticism: My conclusion that there is indeed a loss of vacuum assist is by having the engine running, then turning the engine off. After turning the engine off, I depress the brake pedal until it becomes firm underfoot. It takes about five applications of the brake pedal with the engine off to deplete the residual stored vacuum in the booster, and then the pedal becomes firm/hard to depress.
After starting the engine, then letting it sit idle, engine not started for approximately 24 hours or longer, the brake pedal is firm/hard to depress, just as it is if I depress the pedal 5 times immediately after turning the engine off.
Then after starting the engine again, the vacuum reserve is again replenished and the cycle can be repeated.
I suppose a vacuum gauge could be inserted in the system, but there isn't a convenient port to access vacuum at the booster. All of the service visits have confirmed that there is indeed a loss of vacuum; just no resolution to the root cause and a solution.
Because of this I am confident that there is indeed a loss of vacuum issue, that at least for me, would be hard to dispute.
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@Autobiz Definitely replacing the aux pump will fix if it is broken but most of the posts in this discussion are about loss of vacuum after the car sits off causing a hard brake pedal when starting. No codes present nor running erratic as your video states. Several with the hard brake pedal have even had the aux pump replaced as well as the booster and seals with no improvement for that particular issue. It certainly could help some but it isn't a "for sure" as some have already tried that.
"One size doesn't fit all."
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