Readers Respond To Unintended Acceleration

Jan. 10, 2011
Readers engage Bob Pease on the subject of cars that run away with you.

Greetings Bob;
I applaud your dispersal of this data (see “What’s All This Unintended Acceleration Stuff, Anyhow?”) (Thank you. I’m glad I did it. The recent disclosure of Toyota’s payment of $10 million to the family of four who died in a Lexus with a bad floormat at 120 mph does remind us that this is a serious business. The driver was a policeman. Too bad he didn’t know how to turn off the key. /rap)

I learned this in my driving instruction from my father, many years back. (Good man. /rap) Back then, the older vehicles on the farm were prone to sticky throttles and such effects. The idea of rubbing a guardrail or other objects on the side of the road was more for downhill skidding on snow or ice but it holds true here. And turning off the key is, as stated, the last resort. (Not at all. Driving into guardrails and rocks is the last resort! /rap)

Care is required to not lock the steering, especially in a near-panic situation. (If you reach for the key and turn it off right away, you can avoid the panic. /rap) Your suggestion to practice this is very appropriate. (Check. If you have a newer car, do you know what it feels like with the engine off? I’m sure you can guess. It’s heavy! /rap)

I am reminded to go over these practices with my wife and daughter, who are not good at driving in snowy weather. And no one knows when unintended acceleration will strike. (If you don’t practice it, that is when it will strike. If you do, it won’t. /rap)

As for the note on road hogs, Colorado also has a law. If a vehicle has five or more others behind it, it must pull over at the first available safe stopping point. And it is enforced. I have seen a ticket issued when the patrol car was the fifth car.
Russell Purkey

Hi Russell,
I am delighted! When that guy gets ticketed, somebody should make sure it hits the newspapers! There’s a lot of two-lane roads in Colorado, and this can make them much safer. Thanks for writing!

Beast regrds.

Hi Bob,
I just read your column regarding unintended acceleration. Regarding the Audi UA events, I believe those were traced to EPROMs that were not programmed with enough charge on the floating gates for the logic states to be permanent. There used to be a “development” programming algorithm that would make it faster to erase the devices and make them last longer. The downside was that the programming wasn’t “permanent” and bits could start to flip, and they apparently did. Another case of the digital world really being analog, as you have often pointed out over the years!

(One guy told me that the fuel-injected versions of the Audis that came to the States had a screw-up in the venting to the duct-work and manifolds, but the carburetted one that stayed in Germany had no such UA problem. /rap)

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Regarding the UA in some of the hybrid Toyotas and similar cars, I never understood how people could be so confused and not do something obvious like turning off the ignition (without locking up the steering wheel) as you pointed out, until I drove a Prius hybrid as a rental car. The user interface is horrible with respect to the “key,” which is really just an RFID fob, and the complicated sequence to power the car up and more importantly power it down.

I found the sequence totally counterintuitive given my 31 or so years of driving cars with conventional user interfaces. The required sequence doesn’t match what most drivers today are used to with a mechanical key and a switch that controls the engine. After driving a car with such a miserable user interface, I can understand how people under stress, such as a UA event, could become flummoxed and make bad decisions that have tragic implications.

Best regards,
Gavin M. Monson

Hi Gavin,
Several people told me about this horrible interface. They asked me, “What am I supposed to do to defeat UA? If I need to turn off the engine, I have to push the power ON/OFF button for at least 3 seconds.” I told them to beat on the Toyota dealer until they get a story they like.

Beast regrds.

I just read your column about what to do if the engine won’t slow down when you take your foot off the gas. I was surprised you didn’t mention the easiest thing to do, which is to brake hard. The brakes on a car or light truck will safely dissipate energy at about 10 times the rate the engine will generate it.

(Yeah, but only for a short time, and only if they are in good shape. Using brakes may be jolly fine. But at the first hint that they aren’t working, you have to turn off the key, or shift into neutral, real fast! Faded brakes are something I rarely bump into, but I know it’s really serious. If you are going to just tromp on the brakes, don’t screw around. Get the car to a stop very promptly. Putting on the brakes real hard at 0 mph wastes zero energy. At any other speed, most cars can’t handle those kilowatts. /rap)

This is easy to prove by timing your 0-60 acceleration time (Yes, I have a calendar. /rap) and then your 60-0 deceleration time. In the 60-0 test, you’re limited by tire friction, not by brake energy absorption. But in stopping a car with a runaway engine, tire friction doesn’t enter into it and you can put even more energy into the brakes. Yes, if a timid driver rides the brakes with the engine racing, the brakes will overheat and fade. But if they brake hard, the brakes will slow the engine and kill it before the brakes overheat, even at full throttle. (I think you are correct. But turning off the key can do even better. /rap)

This is doubly important since turning off the ignition will not necessarily stop the engine (That concept is unclear to me. /rap) if it’s running fast enough, (Okay, what does that mean? I never heard of that. We are really talking about engines that keep running without the ignition on? I never run an engine that hot. /rap) unless it’s one of the newer ones with a fuel solenoid wired to the ignition switch. (Which I do have on my Beetle. It’s a newer, modern Beetle—1969. /rap)

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My father had this experience years ago after a pack rat built a nest on the exhaust manifold of a little-used car. At freeway speed the pack rat nest caught fire, heated the throttle cable, and melted the plastic lining in the end of it. After the fire went out, the cable was stuck in the wide-open position by the then-congealed plastic. As my father exited the freeway, he realized the throttle was stuck. He turned off the ignition, but it kept running either on compression or glowing carbon. (Really! Then I guess he has to remember the next stage: shift into neutral, and let it blow! /rap)

The brakes were sufficient, however, to slow the car to the point where the engine stopped. If he had panicked, he would have collided at 70 mph with a full four-way four-lane intersection full of stopped cars. I think it would be good to mention braking hard (Not just “braking hard” but “braking seriously hard” to get the car stopped before the brakes die (fade). /rap) because that’s something even a panicky person is likely to be able to remember to do.

And by the way, I have no use for the drive-by-wire throttle controls. There are just too many things that can go wrong, and by the time you add all the safety interlocks needed to make it fail-safe, it would have been simpler and cheaper to run a mechanical linkage with a stout spring located right at the throttle plate, like all vehicles used to have.
David Sherman

Hi David,
Yeah, man, I’m with you. It seems that my advice has two prongs: one for stick-shift drivers, and a completely different one for slush-box drivers. The advice that is most natural for slush-box drivers (just shift into neutral!) is different from the advice for stick-shift drivers (turn off the key quick and it will slow down).

Yesterday, I was driving my wife’s RAV4, and I turned off the key, and it just slowed down, and I still had power steering, and I still had power brakes, and I still had engine braking (which would be useful on a downhill). Slush-box drivers cannot imagine this!

Conversely, if I were on a flat road, as soon as the engine died, I’d shift into neutral and see how far it would roll (unless I was on a tough downgrade). Most slush-box drivers don’t even think about engine braking, unless they had already downshifted into second or lo.

Beast regrds.

Hi rap,
My first and only UA was in a beater 1980 VW diesel Rabbit with bad rings. I had used it only for city driving, 35 mph max, and except for a little smoke at that speed I considered the hundred bucks I had paid a bargain. That was until I drove on the interstate. At about 50 mph it took off and flatlined at about 85 without any accelerator pedal at all, no key either. (I dunno, how do you convince a diesel to quit? /rap)

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This was accompanied by white smoke that was so thick it totally obscured the dozens of cars I had flown past during the run up. Foot brake, hand brake, shoulder, exit in that order, then park until the shaking stops. To parts store for rings, gasket set, etc. Nothing in the owner’s manual or service manual. This was before the Internet and Google. My pulse rate jumped up just writing this. I haven’t read anything about this anywhere since.
M. Keith

Hi M.,
Didn’t the VW agency have any advice on how to shut off the engine? They Betta! Thanks for writing.

Beast regrds.

Like you, I prefer Volkswagens, although I happen to like their TDI diesels. I was at first astonished to see that they use a potentiometer as their throttle position sensor. (I know a guy who put an AB type J on the control for the throttle on an F-86. These pots are very reliable. /rap) Why would they use a wear-prone mechanical component like that, and not a sealed optical encoder of some sort? Then I got to thinking about the UA problem and how much easier it would be for the ECU to detect a faulty pot. A missing bit or two from the encoder could ruin your whole day. (Uh, yeah.... /rap)

Since VW/Audi was one of the first companies to get dinged for UA, this is not a surprising approach. The pots do wear out, though. One other UA mode peculiar to turbodiesels is turbo bearing failure. If engine oil starts spraying into the intake manifold, the engine will actually run on its own lubricant—for a short while, anyway. Turning the ignition off doesn’t help. Best bet for those of us with stick shifts is to put the car in fifth gear and stall the engine with brakes before it self-destructs.

I don’t know how you’d pull that off with an automatic. Pull over and stuff a rag into the air intake? (Yeah, put a sock in it. /rap) Yet another reason to buy a car with a manual trans.

Jon Wesenberg

Hi Jon,
I sure agree.

Beast regrds.

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