[blashyrk]

I am completely ignorant of all things automotive. I was under the impression that any relatively recent (15 or so years) ICE car also operates by way of a car computer, and that stepping on the gas pedal is just a way to politely instruct the computer that you would like it to apply throttle. And that for even more recent cars this also applies to braking (since the newer cars can brake automatically). Have I got it all wrong?

If not, what's stopping a "traditional" (ICE) car from (mis)behaving in a similar fashion in some catastrophic circumstance that would damage its computer?

[left-struck]

You’re sort of right in your assumption but there’s a lot of context missing. First, the time period is more like 30 years for cars having engine control units (ecu), but most car up until 10 years ago or so had hard physically wired throttles where you stepping on the throttle pulled a physical cable. If that cable doesn’t get pulled the engine doesn’t get enough air to go really fast no matter what the ecu tries to do. More recent cars have fly by wire throttles meaning they are like electric cars in that sense.

An ecu has a far more complicated control algorithm than a electric motor controller. If it were suddenly damaged it’s more like that the engine would fail to run at all then run out of control because the ecu needs to control the airflow, fuel and spark position for the engine to run, if any of those fail to work, or stop firing at the right the exact time they are required the engine will just stop or run very poorly. I actually think this is true of electric vehicles too, it’s far more likely to stop the motor working than to have it run out of control, unless a wheel speed sensor is damaged or something.

A petrol car can be placed into neutral if all else fails, the engine will run out of control but the car wont. Also the gearbox controller is typically a different computer from the ecu.

The brakes on any car should be able to over power the engine. This is not a challenge for 99% of petrol cars because the torque they output is tiny compared to what a brake system can apply to the wheels. If you slam on the brakes the engine doesn’t even come close. Idk about other countries but in Australia this also applies to electric cars that are road legal, it’s a requirement.

the ecu is usually located in the passenger cabin or sometimes next to the battery quite deep inside the engine bay.

The only thing that would cause a petrol engine to really go out of control would be if it was fly by wire throttle and that throttle position sensor was broken in the particular way that it’s reading as full throttle. Idk if manufacturers do this but it wouldn’t be hard to design a fly by wire throttle that when it fails the ecu will see it as closed not open.

Anyway I don’t think it’s much of a concern for electric cars either tbh.

[boricj]

> most car up until 10 years ago or so had hard physically wired throttles where you stepping on the throttle pulled a physical cable.

More like 25 years ago, at least in France. The 2001 Renault Clio 2 I'm driving has throttle-by-wire, the newest car I personally know of with a mechanical throttle is a 1998 Peugeot 205, the last model year of a car that debuted in 1982. I doubt any European car manufactured after 2001 has a mechanical throttle, if only because of European emission standards.

> The only thing that would cause a petrol engine to really go out of control would be if it was fly by wire throttle and that throttle position sensor was broken in the particular way that it’s reading as full throttle. Idk if manufacturers do this but it wouldn’t be hard to design a fly by wire throttle that when it fails the ecu will see it as closed not open.

On the Clio 2 car, there are two redundant linear potentiometer tracks. If the dual measurements don't match or if either sensor is disconnected, the ECU will default back to a slightly higher than idle throttle.

[left-struck]

> On the Clio 2 car, there are two redundant linear potentiometer tracks. If the dual measurements don't match or if either sensor is disconnected, the ECU will default back to a slightly higher than idle throttle.

That’s really neat. I was thinking something along the lines of having a microcontroller with a good adc right next to the throttle pedal and its angle transducer (hall effect would be better) and having that microcontroller send a digital signal. If the ecu can’t make sense of the digital signal or it is missing, just set the throttle to idle. That’s a solution that would be reasonably cheap today though but not 25 years ago.

Anyway in my experience most Japanese and Korean cars didn’t have fly by wire until the 2010s

[grecy]

I once had a diesel engine runaway (google it, the engine ran on its own oil at some insane rpm). I put it in neutral until the engine seized. Scary stuff

[left-struck]

I believe petrol engines can do this too, and I didn’t mention it for petrol engines because the performance of the engine in that state won’t be anything like what it’s capable of, the rpm will go high but if you put any load on it the engine won’t be outputting a lot of torque or power. If this happens in a manual just push the brakes really hard while the car is in gear and clutch released, it will stop the engine. If it’s auto I guess you’re buying a new engine lol, but it’s not like the car is going to run out of control if you just stay calm

[Szpadel]

why not put it on max gear with brakes fully pressed? it should not have enough power to continue

[eptcyka]

The correct course of action is stuffing up the air intake to suffocate the combustion, if this is still a viable option. Otherwise, depart from the vehicle and be ready to call the fire department.

[grecy]

I should have done that, hoping to stall the engine. I panicked and really didn’t know what to do. The noise and MASSIVE cloud of black smoke pouring out the back were terrifying. Not a great first drive after an engine swap.

[t0mas88]

Brakes are not usually "by-wire" on a car that is able to automatically brake. The brake pedal is still physically connected to the brakes.

Same for the steering. BMW for example has a method where the steering wheel is physically connected but the computer can add corrections to it via a clever set of gears. See here: https://en.wikipedia.org/wiki/Active_steering

If the computer (or electric steering motor) fails the steering wheel still works.

[lmz]

Nothing. https://en.wikipedia.org/wiki/Sudden_unintended_acceleration has a list of cases, some of them ECU related.