Cruise Control - Emergency Shotoff

For sure, throwing away the fob will do nothing for your situation. I'd suggest shifting into N and depressing both the parking brake and the service brake. Then power off when you can.

 

If there is a problem with the brake switch, the cruise may not disengage. There is a little on/off button at the end of the cruise control stalk, or you can just pull the cruise control stalk towards you to suspend it

The cruise in my Prius and my FJ operate in the same manner. There are 3 methods of disengaging it

I've never tried it, but I suppose you could move the shifter to the N position and hold it there. Doesn't that shift the Prius into N?

I haven't heard of cruise control going haywire in a long time. Back when cars had carburettors, and vacuum diaphragm cruise control, it was possible to have it jam.

Since modern electronically controlled cruise is part of the entire vehicle control system, I've never heard of any going haywire. Usually they will failsafe and not work at all

In the case of the Prius, if the brake switch fails, as was reported for some 2004-2005 models, you can't boot up the car. The Prius must sense the brake pedal being applied before it will boot

 

The Prius has a Hybrid Vehicle ECU, the main control computer that is connected to:

• cruise control resistor network and switches (the stalk)
• brake light signal
• shifter resistor network and signals
• accelerator pedal Hall-effect (NHW20) / pots (NHW11)
• vehicle start control computer systems

So let us assume the "cruise control" runs away, first hit the brakes and see if it stops running away. If not then it suggests not only is the HV ECU ignoring the cruise control settings, it is also ignoring the brake light signal.

Next, shift in "N" and steer and brake to a normal stop at the safest place possible. But what if the shifter doesn't work? Again, the HV ECU seems to be ignoring this additional input.

Stab the accelerator and see if the HV ECU is listening to the accelerator. Sometimes an extreme position can cause hardware/software systems to "wake up" but let us assume nothing happens. Again, the HV ECU is ignoring your inputs.

Try the power button and hope the HV ECU is listening to the vehicle start/stop system. But the HV ECU may be running away.

The last option is to push the brake pedal hard and force the Prius to stop. You may need a new brake job when done but that is a better problem to solve than traveling in excess of 100 mph down the highway ... unless the road is clear and you have the time.

At 100 mph your fuel consumption will be a little over 22 MPG. Assuming you have a full tank, 11.9 gallons and about 11.2 gallons usable, you are looking at a little over 242 miles that should take about two and a half hours to run out of gas. I would recommend using your 'hands free' cell phone to call 911 and report the problem. Ask them PLEASE DON'T PUNCTURE THE TIRES AT THIS SPEED. You may get a police escort along segments (any excuse) although they may have to do it in shifts. I would recommend I-80 between Cheyenne and Rock Springs WY for this failure.:bolt:

Bob Wilson

ps. The police may ask you to speed it up along this route ... Just let them know you are going as fast as the run-away Prius can go and everyone is pedaling.

 

Your brakes can pull you down from 60mph in 120 feet. It takes nearly a thousand feet for the engine to accelerate you to that speed. That shows how powerful the brakes are compared to the engine - you would have no trouble stopping a "runaway" Prius with the brake pedal as long as you push hard on it. This is also why those claims of runaway Audis that could not be stopped with the brake pedal are so bogus.

 

I'm not the most technical expert on Prius, but I think this has more to do with electronic engine control than anything with the Prius in particular.

Put another way, I think a lot of newer cars are 'fly by wire' where there's no physical connection to the throttle, and everything is handled by computers. So, yes, if there are multiple sensor failures in a particular order and/or the computer software finds a particularly nasty way to behave, it's possible a Prius (and I suspect about any new car) could run away from you. I think there's a Steven King movie about this somewheres <grin>...

If that worries you, you don't even want to know the complexity of what's going on in larger airliners today, where there's no physical connnection to the aircraft controls (you ummm can't just turn it off...that would be bad, bad).

If you want to run yourself in a panic, I poked around and found this website...Software Horror Stories


Myself, worse comes to worse, I'd try N, then power mode, then the parking brake gets slammed on, and we slolam to a stop (worst case).

BTW: The car is pretty smart, I can tell you shifting to R when going forward automatically causes it to just switch to N. It was much more painful/expensive with 'manual' transmissions... And, I'd bet at speed, it'd switch to N no matter what.

Unfortunately, without going Luddite, we have to trust some of these things.

 

Sorry, I forgot to explain how the HV ECU works with the transaxle and inverter. All of the 'gears' are implemented by the HV ECU triggering the inverter to switch on or off the powerful transistors (IGBTs) that operate MG1 and MG2. In this case we are assuming the HV ECU continues to provide properly timed signals to the inverter so the transaxle continues in "D" while ignoring all of the operator interfaces and staying stuck "ON."

Also, the engine ECU operates in response to the requested power from the HV ECU. So we have to assume the HV ECU failure mode also includes commanding the engine ECU into full power mode. There is no independent control of the engine or transaxle.

Bob Wilson

 

shifting into N or B tend to kill the cruise control. pushing the park button forces the car into N above 8mph... much easier than holding N while in an emergency.

 

Go out to your Prius. Press the power button. If it's warm out, and the Prius has been recently driven, the gas motor probably won't start

Now floor the gas pedal and keep it floored. This will command the gas engine to instantly start. Keep it floored. It doesn't rev very much

The Prius is like my FJ in that the gas pedal is nothing more than a poteniometer. There is no direct connection between the gas pedal and the motor. There is also no separate link between the cruise control and the gas pedal

If the cruise control is scaring your wife so much, tell her not to use it

 

Re: Cruise Control - Emergency Shutoff

I agree with Jay's comments. If you floor the accelerator when the car is in P, you will be lucky to get the RPM above 2,500.

In an emergency situation, regaining control of the vehicle is the main issue. Do whatever it takes to achieve that objective.

I would not worry about damage to the Prius engine caused by overreving. The likelihood of damage is minimal and the cost of potential repair minor. On the other hand, if you cannot regain control, the potential damage to your health and the car is quite high and possibly catastrophic.

 

Push the brake pedal to the floor and hold it there. Unless the brakes are faulty you will stop. A person who cannot press the brake pedal hard enough to stop a car should not be driving.

 

It's pretty simple,,,If you are scared about it, don't use it!

Icarus

 

It's not that simple. The Prius cruise control is built into the ECU, and the only way it can fail is if the ECU goes crazy, or an improbably large number of switches fail simultaniously. Here is the kicker: if the ECU goes crazy, it can command full throttle with our without cruise control being on. You can't get away from this sort of risk in a modern world. You have to trust that the engineers did their jobs, and if not, be ready to press hard on the brakes. The odds are much greater that you will be killed by another driver talking on a cell phone (or watching TV on his MFD!)

Tom

 

Someone else recently reported a horrible 'jump start' experience:

How much do you want for this horribly dangerous, runaway car?

Bob Wilson

 

Tom

I would much rather have to deal with this sort of "risk" than return to the Good Old Fashioned way of doing things. Back in "the day" it was far more common to have a problem with a stuck gas pedal or cruise control, as these were entirely mechanical systems

I mentioned the example of the older cruise control that used a vacuum diaphragm servo, directly hooked up to the carb linkage. Any number of things could go wrong with that gadget, causing it to actually jam

Or how about we just go back to carbs with return springs? When I was 15 I got a '67 Chevy pickup, a real trashed up, used up, POS with a 327 V8. I put a new carb - actually an old carb I scavenged from the junkyard - onto that thing and forgot to hook up the return spring

Went to fire it up and that motor started screaming. So I had to kill the ignition and scratch my pointy head until I figured out the spring was laying on the intake manifold

How often do you hear of a car just running insane? A lot of the reports of "unintended" acceleration are really the driver stepping on the gas, not the brake

One area I think *does* need addressing. At one time, with an automatic transmission, the brake pedal was a very wide pedal, compared to the skinny gas pedal. Now, the brake pedal resembles a 1960's Chevy pickup, a square thing. I think it is possible for a wet, snow covered, or muddy boot, to more easily slip off a small brake pedal.

Not to say design defects can't cause issues with stuck throttle blades. For example, modern emissions - PCV - operated in extremely cold climates will have a lot of moisture in the intake manifold. In bitter cold temps, this moisture will then freeze on the throttle blades, causing them to stick.

There have been recalls issued over frozen throttle blades, and it seems most car makers have had this issue with fuel injected engines. Why do you think we have throttle bodies that are heated with engine coolant? Which is why it's a really dumb idea to bypass the TB heat to gain a few precious HP, if such a gain is even possible

Oh, and one thing about a lot of new cars made since early 2000's: if the driver is convinced the car ran wild before the crash that popped the airbags, the black box will have recorded whether the driver had the seatbelt on, whether the driver had applied the brake, speed at airbag deployment, and whether the driver had the foot on the gas pedal

Our new Prius drivers are aware there is a black box in their car? Right? Before they start making accusations of the car running amok

jay

 

Richard

I tried a little science experiment today in the rain. I took my Prius out on the highway at about 80 km/h, making absolutely sure there were no cars behind me.

I floored the gas pedal with my right foot, and I then quickly stomped the brake pedal with my left foot. It was as if I hit a brick wall, it appears the Brake Assist kicked in

So I drove back to my place and took out the FJ. Same conditions and guess what? Same result

jay

 

Tom

Ok, still thinking about this. What is one external event that can simultaniously drive the ECU into a frenzy, and cause a large number of software/hardware switches to also fail?

EMP

I would have to work out the math of mean burst height, weapon yield, and other factors - as I'm sure you like Calculus almost as much as I do - to figure out energy yield. Thing is, such as event would most likely kill the coil packs anyway, so the car would just coast to a stop

Another way to invoke EMP that doesn't involve horrible nuclear weapons exchange would be a largescale Coronal Mass Ejection. Depending on polarity at the time of CME, and how relativistic electrons interact with the magnetosphere and aural electrojets, one could expect a large EMP event

I'm thinking of the 1859 Carrington's Flare. At the time, telegraph systems were knocked out, sparks were flying off the equipment and the ground rods were glowing red. Even today, long fuel pipelines in Sweden will have anywhere from 5-80 amps of current in them due to induced GIC

I guess the point I am trying to - poorly - get across is that is would take a rather improbably set of circumstances to make any modern car run amok. We have much better odds of croaking in a car crash when a s***faced driver runs a red light

jay

 

Ding ding ... we have a winner! The brake will ALWAYS beat the accelerator on any auto. In other words, there is no risk.

... Brad