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Discussion Starter #1
6/22/2017 11:37 AM - Called GM to indicate that I believe my vehicle is unsafe to drive although two separate dealerships have indicated it is safe.

Vehicle: 2012 GMC Terrain SLT 4 Cylinder FWD just under 60k miles

The vehicle is applying brake assist (full brake force, essentially slamming the brakes for you) when you tap the brake quickly even if there is no force behind the pedal, and therefore the system is reacting prematurely which could cause a rear end collision.

The vehicle should react in a way that you would expect, and this is not what you would expect while operating the vehicle.

I have had this vehicle for 5 years and have never had this problem until recently. I have also failed to recreate in on a newer GMC vehicle (different model) or a Toyota Camry. So I do not think this is normal vehicle behavior.

I was able to reproduce it in a similar terrain that Williamson Cadillac found on their lot, one with a few miles and a few years old, so it seems to be a systemic problem and may be grounds for a recall. Because the vehicles are in fact older, it may be an issue that results over time as a result of normal wear instead of outright defective parts.

The first time it happened, I was on the highway going 60 mph and someone traveling slowly entered my lane and so I went to slow down quickly, however I did NOT slam on the brakes and the vehicle went to apply full brake force and scared me.

After that, I figured out how to reliably re-create the issue. Again, this is by driving the vehicle at about 30-40 mph, make sure there is no one behind you, tap the brake quickly but do not slam the brake, brake pedal application speed is the issue. If you slam the brake, of course the expected response would be that the vehicle stop quickly and abruptly.

You can see how this could be problematic. If someone cuts you off and you tap the brake quickly to slow down, and the vehicle slams the brakes, you have a very good chance of getting rear-ended by someone following too closely or not paying attention.

I have also found the portion of the owners manual that explains the system that I think is at fault.

6/23/2017 12:52 PM Today GM Called me to tell me that they are closing the case since the dealer said it is operating normally, they would be closing the case. They refused to provide it in writing even though I explicitly requested it. I explained to them that I believe there is an issue that needs to be escalated, and that it is not safe to drive, and after 18 minutes on the phone, the young lady essentially forced me off the phone and hung up. They record those calls so you can request that call be handed to the NHTSA. The call with GM was at 11:45 am and lasted for 18 minutes on 6-23-2017. Phone number that called was 1-866-790-5600
 

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I think your best bet would be to get rid of your POS, and trade in on a Toyota before you get into a serious accident. Not worth your life.

See ya !

BTW - I have been following just about every post on this board, and AFAIK, you are the 1st to report this problem.
 

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It seems what you have described indicates the system is working correctly. You indicated that you 'tapped the brake quickly" when this occurred. The manual states that this system will activate when the operator 'quickly and forcefully applies the brake".

Are you sure it is not a transmission issue? Many 4-cylinder owners (including myself) have at times experienced a 'bucking', particularly in ECO-mode when braking and re-accelerating.

Lastly, having your first post be a rant about a perceived safety issue is a little odd. Makes many think you are here just to stir the pot.

As RIT noted, this is an EXTREMELY rare symptom.

Any brake service done? At some point, the brakes need servicing (even if they don't have to have the pads replaced) just to lubricate the slide pins. Overall state of maintenance? Any other issues (ie: CEL, etc.)

In the future, I would word your posts as a request for information or feedback (ie: Has anyone ever had this experience .... and then explain your symptoms) and then explain why you are concerned. Coming out and bashing the car on a board dedicated to owners (who, in most cases, like their vehicle) is going to get you little response or compassion.
 

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Discussion Starter #4
The issue is that I have run out of options since both the dealers and GM have ignored the issue. My goal is to get GM to pay attention and to warn other drivers that may have a similar issue. It may be rare, or it may be that someone who has this issue may not know it is an issue. I can't imagine that if it was as rare as is expected that at the same dealer that I was getting it looked at, they had another one that has the same symptoms. The dealer rep there experienced it in my vehicle and the other vehicle, however they said it was likely normal, but it wasn't like it was a textbook response.

As for it being normal behavior, pressing the brake quickly in a fashion that ends up being a fast tap should not elicit a full panic stop reaction. I have now tried in three other vehicles, and i cannot induce that behavior even by pressing the pedal much faster and harder. 2016 yukon xl denali, 2016 camry, 2016 kia sportage. In my car, a simple tap of the brake elicits the brake assist system until the abs system kicks in.

The reaction is correct, however it is coming with the wrong inputs as the amount of force of the brake should not tell the vehicle to apply the brake assist system.

The way that it is functioning will likely cause an accident if someone in normal traffic slows quickly and I have to apply some force, but may not want or need to stop completely and then I can suffer a rear end crash. I have driven many vehicles in my life, and have never had this happen, including in this vehicle until recently.

And I love my vehicle, and I used to love GM. I am sure there are not many people on this forum that have owned a yukon with quadrasteer. My biggest issue is that GM blatantly ignored my request for an investigation even though I begged and pleaded with them to send someone out to make sure it was safe, which if they did do I would hope that they would see it is not normal and is a huge safety issue.

As for brake work, after that issue started, I also had some brake work done, so if there was any maintenance needed they should have done it. They cut the rotors and replaced pads, but the issue persists even after that brake work.

I wish I could record what is happening but it is difficult to record it adequately or put into words that the inputs I am giving the car in a way that makes sense.

I have submitted the issue to the NHTSA but that will likely yield little to no benefit. I just want a safe vehicle to drive. And I cannot in good conscience sell my vehicle to someone because I don't think it is a fair thing to do, so I am stuck with an expensive safety issue.

If you want any other clarification, I am happy to give it. I am not here just to stir the pot, I am genuinely concerned. If you were nearby i'd even invite you by so you can experience it yourself.
 

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You should contact NHTSA to check for issues and file a complaint if you have concerns that GM corporate has not addressed.

I'm new here, but I've read numerous tales of brake assist in a wide variety of vehicles going above and beyond, and I won't have it in my cars.
 

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Disable stabilitrac and see if you can still do it. I'm pretty sure the only thing your Terrian is doing (or able to do) is activate the ABS system. This will make your braking feel more effective on dry pavement.

Either disable Stabilitrac or pull the ABS fuse and see if it is better. Even if it's not a panic-stop, a sharp jab of the brakes probably will activate that ABS.
 

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Disable stabilitrac and see if you can still do it. I'm pretty sure the only thing your Terrian is doing (or able to do) is activate the ABS system. This will make your braking feel more effective on dry pavement.

Either disable Stabilitrac or pull the ABS fuse and see if it is better. Even if it's not a panic-stop, a sharp jab of the brakes probably will activate that ABS.
I always thought ABS kicked in once the system detected you had pushed the pedal firmly down and held it there - not simply a "sharp jab" at the pedal.

Personally, I don't drive the way the OP described: I coast and hover over the brake, possibly applying steady even pressure to slow the vehicle, if necessary. Stabbing (or "tapping") at the brake pedal is not good driving technique, IMO, and frankly - I could see how it might confuse the brake system.

My advice to the OP is to change the way you drive. Coast more. Try *not* to use the brake *at all* if you can help it. One thing I can't stand is someone continually tapping their brakes in front of me. Very annoying. And in this case, possibly dangerous.
 

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Discussion Starter #8
I always thought ABS kicked in once the system detected you had pushed the pedal firmly down and held it there - not simply a "sharp jab" at the pedal.

Personally, I don't drive the way the OP described: I coast and hover over the brake, possibly applying steady even pressure to slow the vehicle, if necessary. Stabbing (or "tapping") at the brake pedal is not good driving technique, IMO, and frankly - I could see how it might confuse the brake system.

My advice to the OP is to change the way you drive. Coast more. Try *not* to use the brake *at all* if you can help it. One thing I can't stand is someone continually tapping their brakes in front of me. Very annoying. And in this case, possibly dangerous.
The way I am recreating it is by tapping it quickly and it is reliable. That is not normally how I drive, but I need to be able to recreate the issue to show techs etc. However, when I try to recreate this issue in any other car, it doesn't happen, no matter how much I try to get it to happen. As for trying to not use the brake at all, try as hard as you might in miami traffic and that isn't really an option haha But I appreciate the suggestions. If this were a driving style issue, it would have been happening for the 5 years I have owned the vehicle as well as happen in another vehicle.

As for it being the ABS, as I understand it is the brake assist system, and then that system applies UNTIL the abs kicks in. ie. the system applies more and more pressure to help you stop until the abs kicks in so that way you don't skid.

I just think its a system that has a defect that shows up over time, and GM just needs to acknowledge it and issue a recall or at least provide the proper method to repair it for a fee.

Just imagine if your car slammed on the brakes when someone cuts you off and you go to slow down quickly. no time for coasting there.
 

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My advice to the OP is to change the way you drive. Coast more. Try *not* to use the brake *at all* if you can help it. One thing I can't stand is someone continually tapping their brakes in front of me. Very annoying. And in this case, possibly dangerous.
I am with you on not using the brakes until absolutely necessary. You must be following my wife a lot. I have to bite my tongue when she drives. She is very cautious with not tailgating, and braking when it would not be necessary. I don't mention anything because she has never had an accident, but neither have it with my risky driving techniques. Well, not exactly "never" for either of us, but it certainly has been decades.
 

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Discussion Starter #10
I am with you on not using the brakes until absolutely necessary. You must be following my wife a lot. I have to bite my tongue when she drives. She is very cautious with not tailgating, and braking when it would not be necessary. I don't mention anything because she has never had an accident, but neither have it with my risky driving techniques. Well, not exactly "never" for either of us, but it certainly has been decades.
I wish it were as simple as driver error. If I were get into a new terrain, 2016 or 2017, or any other vehicle for that matter, it would not behave that way.

The car is activating a system that is supposed to activate when it thinks your maneuvers require a full, panic stop. The type of brake pedal inputs I am giving it should not elicit that response.

They never have before on this vehicle, and suddenly are.

As for the tapping portion, that is just the best way to recreate it. Although not normally done in everyday driving, it is possible to have someone slow down in front of you in stop and go traffic, you tap the pedal and then let go when you realize they are not slowing down enough for you to slow or stop, even assuming adequate following distance and no annoying foot on the brake driving.

In that scenario, my car would apply full brake pressure even though it should not apply it at that moment.

I am not a novice driver, have driven many different styles and types of vehicles, and have never experienced this behavior before in any other vehicle, but alas in my Terrain, which I love, and another used terrain have been able to recreate it over and over again.


But try as I might in any other car, and I cannot under any circumstances recreate that issue.
 

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I forget the name of the authority but you can send an email indicating a issue you have with your vehicle. Transportation Safety Board or something like that ?
 

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It should be as simple as attaching a VDR to your car via the OBII port and replicate the issue while driving. GM then can take the VDR and process the data to see what each system is seeing and doing.

Sadly, that can only happen if the dealer wants to work with you.

I had an issue with my door locks firing open and closing for months on a 2010 malibu. I couldn't replicate because it was random. They gave me a VDR and I drove around for a couple of weeks. When it happened, I activated the VDR and then brought the car in. From the data they found that randomly the vehicle thought the door was OPEN and thus fired the locks open, then when the signal for door open went away, the locks fired down. Turns out it was poor insulation around the door close sensor from rain water / morning due causing a short.

But, if GM is saying the system is working fine, then they won't go any further.
 

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Discussion Starter #13
Disable stabilitrac and see if you can still do it. I'm pretty sure the only thing your Terrian is doing (or able to do) is activate the ABS system. This will make your braking feel more effective on dry pavement.

Either disable Stabilitrac or pull the ABS fuse and see if it is better. Even if it's not a panic-stop, a sharp jab of the brakes probably will activate that ABS.
Tried turning stabilitrak and traction off, still does it.

ABS isn't the issue as the ABS is what kicks in AFTER the brake assist system does. I was hoping that with the stabilitrak off it wouldn't do it so I can at least feel a little bit safer, but that of course brings its own problems since then I wouldn't have the stabilitrak system on.

I appreciate the tip!
 

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It should be as simple as attaching a VDR to your car via the OBII port and replicate the issue while driving. GM then can take the VDR and process the data to see what each system is seeing and doing.

Sadly, that can only happen if the dealer wants to work with you.

I had an issue with my door locks firing open and closing for months on a 2010 malibu. I couldn't replicate because it was random. They gave me a VDR and I drove around for a couple of weeks. When it happened, I activated the VDR and then brought the car in. From the data they found that randomly the vehicle thought the door was OPEN and thus fired the locks open, then when the signal for door open went away, the locks fired down. Turns out it was poor insulation around the door close sensor from rain water / morning due causing a short.

But, if GM is saying the system is working fine, then they won't go any further.

I have thought of that, and I can try that again. I even told the dealer lets compare it to a new one and they said that wouldn't be an apt comparison. I said well if it doesn't do it on the new one, even if the system it uses is different, it would still be indicative that mine is defective. But GM said there was nothing to do, so I guess I have to find another dealer that is willing to actually truly help diagnose it so GM has to respond. Worst part is, there are no codes or anything so I guess the dealer couldn't do much more than that.

Thanks for the suggestion, I will take that route if I find someone who will help me out.
 

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I forget the name of the authority but you can send an email indicating a issue you have with your vehicle. Transportation Safety Board or something like that ?
I reported it to the NTHSA, I think there is the NTSB too, is that the one you are referring to?

Thanks!
 

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Tried turning stabilitrak and traction off, still does it.

ABS isn't the issue as the ABS is what kicks in AFTER the brake assist system does. I was hoping that with the stabilitrak off it wouldn't do it so I can at least feel a little bit safer, but that of course brings its own problems since then I wouldn't have the stabilitrak system on.

I appreciate the tip!
Just to be sure, you disabled stabilitrak and not just traction control? You have to hold the button down for like 10 seconds to disable Stabilitrak.

I'm not that well versed, but I didn't think the brake assist could activate with the Stabilitrak disabled.
 

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Just to be sure, you disabled stabilitrak and not just traction control? You have to hold the button down for like 10 seconds to disable Stabilitrak.

I'm not that well versed, but I didn't think the brake assist could activate with the Stabilitrak disabled.

Yeah, I held it down until both lights went off. I think its powered by stabilitrak but its not actually a stabilitrak function if that makes sense.

As in, the stabilitrak keeps you on your intended path and keeps you from losing control, and the brake assist just applies more brake pressure to help you stop when it detects a panic stop.

That is how I understand it. In either case, having both lights off didn't stop it, the only thing I didn't do was pull the fuse.
 

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I didn't realize that, in addition to Traction Control (TCS) and StabiliTrak, there was also this function called "Brake Assist". Not sure *why* it's needed. If you need to stop the vehicle quickly, you press the pedal down firmly and hold it to make that happen. But this function apparently activates a "booster" module to increase the pressure at all four wheels to make it happen faster? But then it's supposed to only operate until either the ABS activates OR the pedal is released. Maybe the problem is either in the latency of the ABS kicking in, or the delay the "Brake Assist" is using to wait for the ABS to kick in (it's too short). Either way, that might just be a configuration parameter.

Was your vehicle's ECU updated prior to the advent of this problem? Or, did you have your vehicle serviced at the dealer? Maybe your ECU was "updated" and these parameters were modified without your (and possibly the dealership's) knowledge?

If you just tap or even "stab" at the brake pedal, no way should that "Brake Assist" feature engage, regardless of TCS or StabiliTrak being ON or OFF. Those two functions control wheel slip/spin and intended vs actual direction of travel, respectively.

If the dealership refuses to help you, at your next service stop, ask if you can get the ECU program verified. Not sure what that entails ... maybe it's just a version number, but maybe there's a printout that would verify all parameters are set to their correct values.
 

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Yeah, I held it down until both lights went off. I think its powered by stabilitrak but its not actually a stabilitrak function if that makes sense.

As in, the stabilitrak keeps you on your intended path and keeps you from losing control, and the brake assist just applies more brake pressure to help you stop when it detects a panic stop.

That is how I understand it. In either case, having both lights off didn't stop it, the only thing I didn't do was pull the fuse.
I can't tell you exactly where or how, but in theory, you can unplug it. The device should be attached to the brake booster, but I'm going off of a parts listing. It would have an electrical connection.

FYI, I gave my brakes a real quick stab and the nose goes down. I guess I expect that for a new car with good tires and brakes. I can't compare that to what you are feeling though.
 

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I'm not that well versed, but I didn't think the brake assist could activate with the Stabilitrak disabled.
I would think those two functions are independent. On dry pavement, TCS and StabiliTrak are probably not going to engage in most cases, but I could see the engineers still allowing "Brake Assist" to shorten the response time for a quick stop.

There's no indication whatsoever in the cluster of "Brake Assist" kicking in? Certainly there is an indication on the Computer, and maybe the VDR could capture that.
 
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