Problems with unintended acceleration and buffeting

[Cyric]

I've had my sonic for just over a month now, and am at just under 2k miles. I haven't notice any issues with the car, and have enjoyed driving it. I don't abuse the car at all, though I drive about 80 on the highway, I accelerate to that speed pretty gently and gradually. The only issue I've had prior to tonight is the brakes haven't been consistent, despite even pressure on the brake, they seem to grab either too vigorously or not quite enough for the amount of pressure being applies. It's cause quite a few uncomfortable "lock-ups" with the brakes

This evening a whole new problem arose.

I was leaving work and was doing about 30mph, and my engine started to whine as if under load (1.8L Auto) and then I felt it upshift. When it upshifted I let off the gas. Unfortunately I continued to accelerate despite being off the gas. It upshifted again, my speed was now 45. I started to apply the brake, and nothing happened. I did stop accelerating, but I wasn't slowing down.

A coworker ahead of me stopped to let another person turn in, and I start pumping my brakes to no avail.

I ended up using my ebrake to stop. After everyone was safely ahead of me I put on my hazards and let off the ebrake. No movement. I give it a little gas and it sluggishly responds and I slowly roll ahead. I begin to pull over and then the car dropped into Neutral, and then reverse while I continued to coast forward to a safe area in which to stop.

I put it in park, felt the gear change and shut off the car for about 30 seconds. I restarted the car, shifted through the gears and waited to make sure everthing was engaging, and it was. I took a loop around the facility and everything seemed fine.

At no point did I have any warning lights come on. I drove home as if nothing had happened after that.

I'll be calling the dealership in the morning, but after this incident I'm terrified to drive the car.

Any thoughts on what could have caused this?

 

[EVOX_SPEED3]

Wow! Glad u guys are ok! Definitely take it to the dealership first thing in the morning! Sounds like a serious transmission problem, but that doesn't explain the brake problems though. Good luck to you, and please keep us informed!

 

[Cyric]

I will definitely keep everyone posted.

I'm a bit rattled, but thankful not to have rearended my friend. I just hope I'm the only one to every experience this problem. I can't imagine what could happen if someone didn't have time to react.

 

[w[h]o]

Wow I hope the dealership can repeat the problem, future mass recall!?!

 

[wingman]

Wow that is terrifying! I am glad you and everyone else is ok. Take it in asap! Hopefully they can just do a scan to find the fault, or are able to witness the same problem. Best of luck!

 

[SooperSonic]

Ohh wow, I'm glad everyone is ok.

I'm interested to see if the dealer says that there is anything wrong...

 

[gsxr1000]

If that ever happens again turn the key off one click.... not two since that locks the steering

 

[pcguy]

OP, would you please let us know what this turns out to be?:sadbanana:

 

[Cyric]

Well I just got back from the Dealership. I'll start by saying my experience with GM roadside assist was very positive. They towed the car from my home to the dealership with no hassle and very quickly. Whole process took about 40 minutes including the ride there.

I was at the dealership for about 2 hours. I explained what happened and they road tested it twice, and scanned for fault codes.

Nothing came back, which doesn't surprise me since nothing on my dash lit up while this was happening last night.

Unfortunately they couldn't recreate the problem, and as far as they could tell everything is in good working order and they sent me on my way.

My issue with this is that I'm no longer confident about driving the car. To have your confidence with a vehicle completely shattered one month into ownership is unnacceptable.

This is my first new car (my previous vehicles were an 81 El Camino, an 81 C10, a 72 International pickup, and a 2001 Jeep Cherokee) and the entire reason I bought this car after my jeep let go was for peace of mind. I wanted a warranty and at least 3 years of worry free driving.

I only got 5 weeks of worry free driving, and now I'm going to have the thought in the back of my mind about that ordeal happening again.

What if it happens on a busy road, or the highway? What is going to happen to me, or another driver who happens to be present?

What happens if the problem presents in someone else's sonic? They'll have no idea how to react.

Are there any other steps I can take to maybe have a more thourough investigation done? Should I contact GM directly?

 

[Alan]

Unfortunately you are going to have to keep documenting your issues. Every single time you get a hiccup take it to the dealer so they have record of your complaint. Calling GM could help but they will just tell you to take it in for diagnostics (which has already happened).

 

[SonicChris]

I would contact G.M. In a case like this, they will contact the dealership and maybe have them run other testing on your car. After what happened with Toyota, G.M. is going to do everything in their power to find out what happen. Not that your dealership service center doesn't care, but it will be more of a priority to G.M.

 

[Jeffnj]

Sounds to me like the accelerator got stuck! Do you have floor mats maybe it got stuck on that?! Or the accelerator switch or What ever you want to call it that tells the computer how much your pressing the peddle malfunctioned or got stuck in one position

 

[Machine]

Sounds to me like the accelerator got stuck! Do you have floor mats maybe it got stuck on that?! Or the accelerator switch or What ever you want to call it that tells the computer how much your pressing the peddle malfunctioned or got stuck in one position

I would agree on a pedal getting stuck under the carpet. Not to discount anything you said, but there are multiple redundant systems that should have come into action under the conditions you stated.

As far as the accelerator pedal; I have not serviced this system on a sonic, but generally all GMs run a 4 sensor redundant throttle system (which is called Throttle Actuator Control, or TAC). There are two sensors on the Pedal (PPS pedal position sensors A and B) and two sensors in the throttle (TPS Throttle position sensor A and B) all 4 of these sensor are constantly checked against each other on continuous basis. If any of them is more than a predetermined percentage off (which I believe is less than 5%) the whole system goes into Reduced Power/Limited Throttle mode. Throttle is generally limited to 20 or less. Sometimes it is held at Idle in extreme cases.

As far as braking goes, most cars brakes DO NOT have the ability or overcome an engine that has moderate to heavy throttle. And even if they do, they will quickly overheat and fade. That being said, I believe that the system will also go into Reduced power if the Gas and brake are held at the same time for more than about 2-5 seconds.


Again, my guess is that your pedal got caught and the brakes couldnt overcome. Believe me, 5 seconds can be a lifetime when your in tense situation and your life is on the line. (its called adrenaline) Check to make sure that your mat is secured, and that you dont have a All season on top of the factory one or something like that.

Best of Luck

 

[Jeffnj]

In any situation where your car starts to accelerate uncontrollably the first thing you should do is apply brake and put the car in neutral as fast as possible. Never turn the key off and risk losing the ability to steer

 

[pcguy]

My experience with turning the key off (especially if you do as one suggested earlier in this thread and only turn the key one click so that the steering doesn't get locked) is that while steering may be a bit more difficult, it will still function. Also though, it may not be more difficult if your engine continues to spin while the transmission is engaged, at least until you have come to a stop.

Don't know for sure how all the above is affected by the electronic (is that the right reference?) power steering that the Sonic has.

 

[LS1notFOUND]

If you vehicle ever starts to get out of control...shift to neutral!

Also did you by any chance possibly hit resume on the cruise control? That would pretty much fit your description for the car accelerating despite being off the gas, and the fact that the buttons are right on the steering wheel I believe. Drive by wire throttles don't "pull away" from your foot like the old cable systems did so it could "appear" like no throttle is being applied when in reality its getting you back up to what ever it was set at, and GM vehicles "mean business" on their way back up to speed I've noticed.

Other than hitting your brakes and it not canceling the cruise, and if indeed you were trying to put that pedal through the floor, it would mean you have no pressure or reduced pressure, in your brakes, that braking system is all mechanical and linkages besides the ABS/Stabilitrak module, and it certainly wont keep you locking all 4 up even it that little computer fails. Please check your brake fluid level keep and eye on that ever changing brake pedal effort, this could be the heart of your problem.

Keep us updated but something sounds off here.

 

[SRGilbert]

Well, in a worst case scenerio, at least you have 10 airbags and Onstar to call for help!

 

[wasteoffilm]

Machine(or others)

Is the event recorder accessible by techs, or only GM? And how long does it keep memory?

To the OP, throw a fit, get GM involved...

We had a customer threaten to sue us (and GM) once. We had just replaced U-joints on a Tahoe, and it came back in a couple of days later with the shaft ripped out, and transmission destroyed. Customer throws fit, gets GM involved. They show up, plug in a laptop to the Tahoe, and find out it was driven long distance, wide open throttle, in 4WD-Low Range. Turns out their kid was drunk and running from the police on and off road.

 

[ronarn]

Is anything right with Sonic?

I've had my sonic for just over a month now, and am at just under 2k miles. I haven't notice any issues with the car, and have enjoyed driving it. I don't abuse the car at all, though I drive about 80 on the highway, I accelerate to that speed pretty gently and gradually. The only issue I've had prior to tonight is the brakes haven't been consistent, despite even pressure on the brake, they seem to grab either too vigorously or not quite enough for the amount of pressure being applies. It's cause quite a few uncomfortable "lock-ups" with the brakes

This evening a whole new problem arose.

I was leaving work and was doing about 30mph, and my engine started to whine as if under load (1.8L Auto) and then I felt it upshift. When it upshifted I let off the gas. Unfortunately I continued to accelerate despite being off the gas. It upshifted again, my speed was now 45. I started to apply the brake, and nothing happened. I did stop accelerating, but I wasn't slowing down.

A coworker ahead of me stopped to let another person turn in, and I start pumping my brakes to no avail.

I ended up using my ebrake to stop. After everyone was safely ahead of me I put on my hazards and let off the ebrake. No movement. I give it a little gas and it sluggishly responds and I slowly roll ahead. I begin to pull over and then the car dropped into Neutral, and then reverse while I continued to coast forward to a safe area in which to stop.

I put it in park, felt the gear change and shut off the car for about 30 seconds. I restarted the car, shifted through the gears and waited to make sure everthing was engaging, and it was. I took a loop around the facility and everything seemed fine.

At no point did I have any warning lights come on. I drove home as if nothing had happened after that.

I'll be calling the dealership in the morning, but after this incident I'm terrified to drive the car.

Any thoughts on what could have caused this?

I've been looking at these comments since the car was released and can't understand why anyone would consider buying a sonic. I never imagined so many diverse things could go wrong with a car. (paint/brakes/glass/engine/transmission/etc./etc.)

 

[Alan]

We value your insight on this matter.