Cruise Control/Brake Failure Incident - CLA 17Reg

[CLAOwner]

Hi All,

Apologies if this topic is in the wrong place, new to the forums!

Over the weekened my wife had an incident in our 17 Reg CLA 180. Whilst driving in cruise control at 50mph, with way more than enough space between her and the car in front, the brakes failed to stop or even slightly reduce the speed of the car, and caused my wife to crash into the car ahead at 50mph, with even the airbags failing to deploy. Fortunately there are no severe injuries to any party.

Whilst the above would be hard to prove/believe, I luckily had a dash cam installed, which shows my wife panicking and clearly saying to the passenger than the brakes aren't working, before showing the crash.

The car is currently on it's way for repairs, and my Mercedes dealership have offered to investigate the cruise control/brakes to understand what happened, but as this was a severe fault, which could have cost multiple lives, I was wondering if anyone had heard of a similar incident?

I also know in the past few weeks there was a story from China where a Mercedes was stuck in cruise control with the brakes failing (I won't post a link as unsure of forum rules), but understand nothing has yet been concluded.

 

[MancMike]

Unless the car in front was stationary when she was doing 50, then she didn't hit it at 50mph. There'll have been a much lower impact speed which is why airbags didn't deploy. Airbags need quite a hit to deploy, as they are in themselves, dangerous.

If it was 50mph impact speed, there'd have been many injuries, especially if the airbags also failed to deploy, and the car would be written off, not going for repairs.

What is your way describing the brake situation as? Did the pedal go to the ground, or did it feel normal, but with no braking happening?


EDIT: For reference, this is what a 40mph impact does to a CLA.

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[CLAOwner]

Unless the car in front was stationary when she was doing 50, then she didn't hit it at 50mph. There'll have been a much lower impact speed which is why airbags didn't deploy. Airbags need quite a hit to deploy, as they are in themselves, dangerous.

If it was 50mph impact speed, there'd have been many injuries, especially if the airbags also failed to deploy, and the car would be written off, not going for repairs.

What is your way describing the brake situation as? Did the pedal go to the ground, or did it feel normal, but with no braking happening?


EDIT: For reference, this is what a 40mph impact does to a CLA.

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For more detailed information, see our cookies page.

Accept third party cookies

Apologies. Looking at my video, the car in front was still moving, albeit fairly slowly. According to my wife, the pedal felt normal at least from what she can remember. From my video, the CLA doesn't look like it slows down at all, after almost 5 seconds of attempted braking from my wife. It's almost as if the cruise control doesn't disengage but surely if that was a fault the brakes should at least slow the vehicle (I'm far from an expert!).

 

[st13phil]

I'm not saying this didn't happen, because I wasn't there and I haven't examined the vehicle, but it's certainly a puzzling failure if it did:

1. Cruise will (should) disengage as a result of just moving the brake pedal, even if there is no significant braking effort applied
2. Even if cruise didn't disengage, it's not difficult to generate enough pedal effort to get a pretty significant rate of retardation. Just try driving along and keep your right foot on the throttle and brake with your left foot at the same time to see what I mean
3. The car has (at least) the radar-based Collision Prevention Assist system that would have beeped if a collision was imminent (did it?), and if it has Collision Prevention Assist it would (should!) autonomously brake too

Is your wife one of those women who take off their high heels and swap into flat shoes when driving, by any chance? If so, she wouldn't be the first one who then left their "other" shoes in the footwell ready for them to jam under the pedals. Just a thought?

 

[CLAOwner]

I'm not saying this didn't happen, because I wasn't there and I haven't examined the vehicle, but it's certainly a puzzling failure if it did:

1. Cruise will (should) disengage as a result of just moving the brake pedal, even if there is no significant braking effort applied
2. Even if cruise didn't disengage, it's not difficult to generate enough pedal effort to get a pretty significant rate of retardation. Just try driving along and keep your right foot on the throttle and brake with your left foot at the same time to see what I mean
3. The car has (at least) the radar-based Collision Prevention Assist system that would have beeped if a collision was imminent (did it?), and if it has Collision Prevention Assist it would (should!) autonomously brake too

Is your wife one of those women who take off their high heels and swap into flat shoes when driving, by any chance? If so, she wouldn't be the first one who then left their "other" shoes in the footwell ready for them to jam under the pedals. Just a thought?

Agree the cruise control should disengage, and even if it didn't the braking should at least be able to slow the vehicle. Neither of which happened.

The CPA system alert did sound (beep on the video which from previous experience I assume this is), yet the speed wasn't reduced at all.
And no, there was nothing in the footwell which could have been caught under the pedals.

I agree it sounds mad. And I'm not sure what I would have believed had the dash cam not been there. Mercedes have said they will bring it in for an investigation but I just wanted to see if there were any other similar experiences.

 

[wu56Shoozz]

Actually.. the first of the Vectras had this whereby it would engage itself and cause chaos as it was difficult to disengage.. I had one once that did exactly this... I knocked mine into neutral and coasted for a bit before driving as normal.. the "Cruise" control should disengage by dipping either the clutch or brake pedals - if an auto, then into neutral will suffice (done this too on a bus of all things...)

 

[st13phil]

The CPA system alert did sound (beep on the video which from previous experience I assume this is), yet the speed wasn't reduced at all.

Does the car have CPA or CPA Plus? If the sensor system worked (as evidenced by the beep) and it has CPA Plus then the obvious question is why didn't the autonomous braking kick in?

I agree it sounds mad. And I'm not sure what I would have believed had the dash cam not been there.

Make sure you keep the dash cam footage safe. Depending upon how MB UK respond, you may need to make a report to the Driver and Vehicle Standards Agency (DVSA) and the footage could be important to their investigation.

 

[KillerHERTZ]

Re: Airbags, its probably a good thing they didnt deploy, they can cause temporary deafness, burns and broken bones (eg nose). plus they generally will write a car off once they have been fired.

 

[CLAOwner]

I have backed up the Dash Cam footage. I have given Mercedes the chance to investigate, but depending on the outcome I know that's the most important piece of evidence I have.

On airbags - Probably best they didn't deploy, but it would be interesting to know if this was on purpose, or if it was down to a fault.

 

[KillerHERTZ]

They will only deploy if needed. I highly doubt its a fault.

(Not aimed at you) but its amazing how many people ive spoken to/read who get annoyed that the airbags didnt fire and assume theres a fault.

 

[CLAOwner]

They will only deploy if needed. I highly doubt its a fault.

(Not aimed at you) but its amazing how many people ive spoken to/read who get annoyed that the airbags didnt fire and assume theres a fault.

Fair point! As I've said I'm no expert. It's a small part of the issue but I was just intrigued whether or not this should have happened.

 

[MancMike]

I've had 3 car accidents where I've bounced off of my seatbelt, and one, I was pretty dazed, the airbag has never deployed. You've really got to have a big smash for them to deploy. It's a bomb in a bag, not a prang detector.

If your car is being repaired, it wasn't hard enough for them to deploy. Your front end and engine would be demolished.

If your airbag system had a fault, the car would not shut up about it.

 

[Dryce]

Hi All,
Over the weekened my wife had an incident in our 17 Reg CLA 180. Whilst driving in cruise control at 50mph, with way more than enough space between her and the car in front, the brakes failed to stop or even slightly reduce the speed of the car, and caused my wife to crash into the car ahead at 50mph, with even the airbags failing to deploy. Fortunately there are no severe injuries to any party.

The brakes are normally on a separate system from the CC. The only interaction is that the switch under the pedal which normally actuates the brake lights also deactivates the CC. If this failed the brakes should still be powerful enough to stop the car.

I don't think the CLA has a 'brake by wire' system so the scenario where the braking and CC systems interact where the CC could override the brakes shouldn't be feasible. (Somebody correct me if I'm wrong). So the brakes are independent of the CC. They should be well capable of stopping the car even with the CC active.

 

[renault12ts]

Just in case, and it should be asked...she was pressing the brake, not the accelerator?

 

[Dryce]

I agree it sounds mad. And I'm not sure what I would have believed had the dash cam not been there. Mercedes have said they will bring it in for an investigation but I just wanted to see if there were any other similar experiences.

What does the dashcam show though?

It can record what's in front of the car and record the driver's reaction to the situation - but presumably not the state of the vehicle controls or the actual application of them. The driver's reaction doesn't actually reflect the state of the vehicle controls or the actual application of tem either.

It may be that the car's own systems record some of the information you need to clear this up. It would be worth asking if anybody knows exactly what a modern CLA records in its internal systems memory that might be of use.

 

[CLAOwner]

What does the dashcam show though?

It can record what's in front of the car and record the driver's reaction to the situation - but presumably not the state of the vehicle controls or the actual application of them. The driver's reaction doesn't actually reflect the state of the vehicle controls or the actual application of tem either.

It may be that the car's own systems record some of the information you need to clear this up. It would be worth asking if anybody knows exactly what a modern CLA records in its internal systems memory that might be of use.

Yes that's what I'm trying to find out when the garage gets hold of it. Knowing very little about car systems, I'm hopeful there is some kind of black box style recording of information which clears things up a little.

The dash cam itself, like you say wouldn't show that as it's only viewing the road in front. But the recording I do have, shows my wife panicking for 4-5 seconds and saying to the passenger "The brakes arent working" multiple times. The car doesn't speed up, slow down, jerk at all or rev more which leads me to believe in no way was she pressing any other pedal.

 

[Dryce]

The dash cam itself, like you say wouldn't show that as it's only viewing the road in front. But the recording I do have, shows my wife panicking for 4-5 seconds and saying to the passenger "The brakes arent working" multiple times. The car doesn't speed up, slow down, jerk at all or rev more which leads me to believe in no way was she pressing any other pedal.

The problem is that this doesn't tell you very much.

CC was stated as active - that makes the failure mode with the driver potentially more complex. Not just the CC behaviour but the interaction with the driver.

If the brakes have failed then the conclusion should be clear cut. You can't really argue with a brake bedal that goes flat the floor and does nothing. The problem is that if the brakes still work then you are left figuring out what actually occured. As has been stated above - the question also naturally arises as to whether a pedal was obstructed.

As soon as CC is mentioned and there is no other clear technical failure then my inclination would be to figure that this is a problem with the control loop involving the car and the driver getting disconnected at the point where the driver has to deal with the hazard. If you have a driver dealing with a hazard and there is any sort of confusion that causes a loss of control then it can compound the situation. The driver is potentially left quite disorientated as to how the situation unravelled - whether that be a technical failure or driver error.

Modern CC systems are quite clever but there are pitfalls. So as an example - a driver with CC active might approach a junction or exit slip road. They had their foot partially depressing the accelerator but not enough to override the CC. As they lift their foot they think they are letting the car slow. Instead they perceive it accelerates (it's not - just not decelerating) and there is a short period - a few seconds of confusion. Normally a driver will hit the brake - and there is no bad outcome. However in that short window of confusion there is a risk that the driver won't react - or that they make a mistake - and the outcome is less good.

So I think you need to look at what evidence can be obtained to clearly determine a technical failure. Which goes back to the current condition of the vehicle and any information it has logged.

And also need to understand the CC system in greater detail - eg. if it is Distronic how does it react if there is no driver input or of the driver depresses the accelerator when it detects an obstacle ahead.

 

[shyam27]

This is crazy, can't believe it would happen in 2018 on any modern day vehicle, let alone it being a Mercedes! Cruise Control technology was being developed right from the 1950's! Can you give us on a scale of 1-10 how sure you are that your wife tried to disengage cruise control with brake pedal? If it's true then I have completely lost faith in Mercedes. I wouldn't even compare Mercedes to Kia and I'll never ever recommend any new Mercedes to family and friends..

Do you have enemies that would come to your house and tamper with your brakes/brake pipes etc? Just asking as I've heard people do this. It should be obvious if anything like this was done..

Also brake should function normally as it's independent from cruise control, however the brake pedal is programmed to 'disengage' the cruise control. With them being linked electronically and with all our pedals communicating with a computer rather than traditional mechanical means, there is the possibility that the cruise control did in fact interfere with your CLA's braking ability.

I'm also curious to know, did the wheels continue to spin after making contact? Did the vehicle in front get pushed forward ferociously by it still being engaged in cruise control?

The unfortunate news is someone is going to have to make a claim through either your wives policy or other party and in this case, it will be your wife at fault. However, there is the opportunity to have an official investigation put forward with Police, DVSA and Mercedes themselves. This will involve going to court, hiring lawyers, fees, doing lots of reading and preparing your evidence. Don't let that put you off though as you will be rewarded if they are found liable for it. Will help if you can have an engineer look over your vehicle to identify and confirm that Cruise Control was defective... Also, do not send it to MB for repairs by any means as they may destroy evidence that it was in fact defective, just a thought!

 

[st13phil]

This is crazy, can't believe it would happen in 2018 on any modern day vehicle, let alone it being a Mercedes!

Calm down - you'll have a coronary

The important thing is that we don't know what happened as yet (if, indeed, there was a failure of the car's control systems).

 

[KennyN]

Is the car an automatic ?

If so and the wife has access to driving both auto and manual cars is it not possible that in the heat of the moment and with an impact pending she panicked and was pressing the third "dead" pedal instead of the brake ?

Kenny