Re: Toyota Runaway Cause: Electronic Throttle/Cruise Control?

No. I just resist stating information as facts known to me when I am repeating things reported by the press. If you review a bunch of web sites you can get a pretty good picture of what happened in this one particualr case.

This site also mentions that the car would lose braking power with the throttle wide open. This is true for any vehicle that uses engine vacuum to provide brake boost, not just a Lexus or Toyota. The booster only stores enough enough vaccum for a few stops. An engine at WOT doesn't provide any additional vacuum. So if your throttle is stuck wide open, and you repeatedly press on the brakes, you will loose boost.

However, I still say if the guy had moved the shifter into neutral, he could have stopped the car. But that is jsut my opinion.

Ed

I tried this technique and there is nothing to stop you from flipping the shifter up to neutral. You might over-rev an engine (especially if the electronics have rebelled) but you will be able to slow and stop. The brakes dont stop working if the vacuum is lost...you just have to depend upon your leg muscles. You may THINK you have lost all brakes, but they are still there.

Ah, but some of the Toyotas are shift by wire. That is, there is no physical linkage, merely a switch that sends a signal to the computer.

And, keyless ignition. The ON-OFF switch sends the shutdown signal to the computer. I have a Prius, and I'm a bit worried.

Supposedly these cars use hydraulic pressure supplied by the power steering pump for braking assist not engine vacuum. Well, that's what I hear anyway.

Odd, ain't it?

It makes good sense, if the engine isn't going to be running most of the time anyway.

The old BMW E28 did something similar. It worked very well, and it included a pressure reservoir that provided considerable braking for a good while after the engine was shut off. It was substantially more complicated than it needed to be and had dozens of seals that all went bad at the same time, mind you. But that has more to do with the implementation than the concept.

Dunno, I have never driven one of the hybrids. I'm still commuting to work in a car with a manual choke. It's paid for.

--scott

The advantage of a vac boost system is simplicity. OTOH, there's cars where fitting that big booster thingie just ain't practical. OTOH, even though your old BMW had it, the system still seems high-tech and exotic these days and my guess is that it's a selling point on high-end cars.

I sure hope that it's paid off. Those things disappeared with carburettors!

The cars I had with chokes were set by pressing the accelerator to the floor once. I had one Brit car with a real dash operated choke - just don't forget to push that sucker back in! :-)

For sure some cars use hydraulic brake assit instead of vacuum assit for the brakes (my 2001 Mustang GT did for instance). However, the reports I read indicated that the Lexus in the California wreck used a vaccum booster (and the Lexus parts catalog supports this).

Hydralic type boosters depend on the engine running to provide hydraulic pressure. You can include an accumulator in the circuit to provide back up boost for sutuations where the engine dies, but this is still limited.

I am not sure what the hybrid vehicles use. A hybrid you can't depend on either engine vacuum or an engine driven hydualic pump to provide brake boost, so I assume they have an electrically driven hydraulic pump to provide the boost but I don't know for sure. Maybe they use the ABS pump....

Yes. I guess even trained professionals can panic.

Ed

Thanks for that info.

That's a good question. I would suppose you could even use the drive motors to slow the car down. Hybrid cars are such a complicated animal.

My guess is that you don't really know how you'd act in such a situation until it happens. Good thing this is such a rare event.

Good question on hybrid brake assist. The power steering system uses an electric motor to provide assist, and so there is no electrically driven hydraulic pump for the power steering system. I would imagine that hybrids use some kind of electric assist for the brakes. The ABS system on a Toyota does not have a pump, just valves that open and close rapidly to modulate brake force to individual wheels.

Yes - only had it happen to me once (coil lost power and so the engine died) but I was running at around 80 at the time and it was something of a surreal experience. I think the split second before I realised what was going on was perhaps stranger, as the car began to slow due to the rear wheels turning the dead engine.

Our truck's old enough to have no engine assist for the brakes at all, so the leg gets a good work-out :-)

cheers

Jules

Pre law.