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Comment by djrogers | Hacker News Reader

Nothing about this story makes sense, and it's so sketchily sourced I'm surprised to see it here on HN.

For starters if the problem was with cruise control, how would opening the drivers side door 'slightly' slow the car to half it's speed? Setting aside the physics here, cruise control would simply increase the throttle until it got back to it's set speed.

Also questionable is the idea that MB would be able to remotely control the vehicle when every system other than the throttle had failed. Brakes failed, ignition failed, transmission failed, but the throttle and cruise control were still hunky-dory? That sounds a lot more like either a complete fabrication or someone who screwed up while trying to hack their car's CAN-BUS...

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FWIW, it was in the Daily Mail too with more detail. That probably still falls under the general category of "sketchy sources" but there are enough specifics it's not obviously totally made up out of whole cloth. But I'd put a lot less faith in any of the details.

http://www.dailymail.co.uk/news/article-5509373/Horror-ride-...

The story is sketchy and if true as written I would have by now expected the major networks to have it on front pages -- with a catchy title this is a sure way to increase views.

But to me that idea that opening the door slows the fly-by-wire car is not outlandish. In fact, this (and unbuckling for a few seconds) were first thoughts I had on how I would have tried to break out of the stuck fly-by-wire mode or at least activate a safer "limp to safety" mode.

Actually, if the cruise control system had some how locked up it would make sense that the throttle was set to some fixed position. Any changes to the aerodynamics of the car would effect the speed at a fixed throttle.

That said, this really is just low quality sensational spam.

>Also questionable is the idea that MB would be able to remotely control the vehicle when every system other than the throttle had failed.

None of these things failed per se, they just weren't under user control.

Cruise control on both of my cars is closer to "set throttle" than "set speed". Neither will increase throttle to keep speed when going up a hill for example.

That's not typical for cruise control; even cars in the 80s with cruise control would increase throttle uphills.

Agreed. I don't think any modern car works on a fixed throttle.

Which is and always has been a downright awful and dangerous feature. Going up a steep hill? Put the pedal to the metal so we can fly past other cars at 65 MPH.

You're really describing a more general issue with traditional cruise control and one of the reasons I rarely use it, especially on roads with any amount of traffic. Cruise control encourages you to keep to a set speed even when that makes you deviate from keeping in the flow of traffic.

Or would be a lot safer and more efficient if everyone just went a constant speed on the freeways. My cruise control also operates he brakes so my set speed is held going up and down hills.

2009 Pontiac and a 2013 Fiat, so relatively modern.

Couple of possibilities then, I suppose:

* They do work towards a set speed, but I'm too impatient and reset the cruise control before they achieve it.

* Cruise control operates differently on cars with manual transmissions. I've never actually observed cruise control behavior in an automatic because it's been broken on the automatics I've previously owned.

I have a 2001 Porsche Boxster (manual transmission). It will maintain speed as long as their is sufficient torque to do so in the current gear (or engine braking depending on uphill or down hill).

Is it possible that you don't have much excess engine power at highway cruising speed and the car is only slowly responding to change in incline?

Quite possible! I'm currently in Kansas or I'd be out finding some hills right now to test this further.

That's not cruise control then, it's... 'throttle hold'? Even the cruise control on my 30-year-old Toyota will vary the throttle as required to maintain the set speed.

Throttle lock. That's what most motorcycles have in lieu of the CC electronics. It's also what happens if you, say, remove the return spring on your throttle body.

How old is your car? Cruise control in every automatic transmission car I've owned (dating back to the 70's) will use enough throttle to downshift the transmission and maintain speed on any freeway hill.

In a manual transmission, then sometimes it needs a downshift and any use of the clutch switches off the cruise control.

My car has a manual transmission and factory cruise control and using the clutch does not disable the cruise control. The cruise control even rev matches shifts.

As mentioned in my other comment, 2009 Pontiac Vibe and 2013 Fiat 500. The Pontiac actually has manual windows, so I wouldn't be surprised if other corners were cut for simpler systems..

Interesting all of the minor variations between cars. Both cars (manual transmission) will also shut off cruise control if I even think about pressing the clutch, although rarely the Pontiac will forget to do that until the clutch is disengaged and the engine is revving high. :)

I've never seen a cruise control that worked like that. Set speed or min/max speed and the tachometer is nailed.

Depends on the car; a VW with automatic transmission has a "speed set" cruise control, the car will change gear and vary throttle at will to keep the speed; won't brake though, except by downshifting.

Dang, even my old hoopty from the 80s would do a reasonable job of keeping speed, and that was in a GM crapbox. There's no chance a modern MB doesn't do so as well.

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