Directly form the factory shop/repair manual for the 2008 Prius.


2. OPERATION DESCRIPTION

(a) Electronically Controlled Brake:

The skid control ECU recieves signals from the pedal stroke sensor, master cylinder sensor and wheel cylinder pressure sensor. Based on these signals, the skid control ECU calculates the necessary braking force for each wheel. The necessary hydraulic pressure braking force is sent to the hybrid control ECU via CAN communication. The skid control ECU receives a braking force (regenerative braking force) signal from the hybrid control motor via CAN communication. The ECU calculates the necessary hydraulic pressure braking force based on the necessary braking force and regenerative braking force.

Rephased/structured for clarity:

2. OPERATION DESCRIPTION

(a) Electronically Controlled Brake:

The skid control ECU recieves signals from the pedal stroke sensor, master cylinder sensor and wheel cylinder pressure sensor.

Based on these signals, the skid control ECU calculates the necessary (TOTAL) braking force for each wheel.

The necessary (TOTAL) hydraulic pressure braking force is sent to the hybrid control ECU via CAN communication.

(In return) The skid control ECU receives a braking force (regenerative braking force) signal from the hybrid control (ECU) motor via CAN communication.

The (skid control) ECU calculates the necessary hydraulic pressure braking force based on the necessary braking force and (Less the) regenerative braking force.

So what happens if the hybrid control ECU is "out to lunch" and never sends the results of its calculation back to the skid control ECU...??

No braking at all...??

Your can press down on the brake pedal with all your weight but unless the skid control ECU opens the ABS/TC manifold ports to allow master cylinder pressure to reach each individual wheel...

 

The documentation clearly implies that the skid control ECU will NOT open the ABS/TC manifold ports to allow hydraulic braking to the wheels if the HSD control ECU "says" it will provide 100% of the braking. So it might not matter how hard your depress the brake pedal the resulting hydraulic pressure may not be ported to the wheels or maybe only a portion provided what the HSD control ECU "reports".



Yes, clearly there should be, SHOULD BE, a "time out" period if the HSD control ECU doesn't report back within a very short time limit, say <10 milliseconds.



But if you look at the 2010 Prius TSB regarding the fix for delayed hydraulic braking in the event ABS disables regenerative braking then it becomes quite clear that NipponDenso has overlooked, until now, the need for this type of time out.



It appears, from reading the TSB, that the early HSD control ECU was sometimes LATE (to busy, too many other more important tasks..??) in responding to the skid control ECU's query and the skid control ECU simply stood by and waited.



Meanwhile......NO braking.

 

I own a 2006 Prius. I learned about holding the gear select lever to the N position for about a second would put the Prius in neutral and drop the engine to an idle by experiementing with it several years ago. I also learned that I could not rev my Prius when it is in Park.

To my knowledge nothing is written anywhere that tells the owner how to do these things.

I took my Prius out on the interstate the day the fellow from California claimed his Prius fully accelerated, floored it above 70 mph, held the gear select lever to the N position and it went into neutral and the engine dropped to an idle. I've also found that gently pushing on the brake and holding the gear select lever to the Drive position will reingage the drive motors while the car is rolling at any speed.

Is anyone aware of any statements Toyota Corporation may have made to instruct the owners of their problem cars what to do in the event a runaway event occurs? None of my Prius friends were aware of how to put their vehicles into neutral. Maybe I've just overlooked it.

 

For me, there remains a rathe strong possibility that Mr. Sikes Prius, ALL HSD systems including the Ford Knock-off/Clones, have a situational/conditional firmware flaw. I suspect the HSD system control computer was continuously executing the "set/accel" function. The HSD system computer was obviously IGNORING the communication signals from the skid control computer that braking was required and therefore it should cease DRIVING.

In that case it may, or may not, pay attention to the shifter position switches.

 

I tried the same thing right after that California incident as well. It will go into neutral as you stated. But the key is you have to hold it in the nuetral position for about a second to take effect, most people don't know this. I did it going 60 mph and it worked.

I also tried turning the power button off, at a much lower speed, but that did not work. I couldn't turn the power off.

So then we had people saying why didn't the guy in California just turn off the power button or put it in neutral? Well, from my experiment, you can't turn off the power. And if you did, you would lose power steering and that would not be good at 90 mph.

I think he could have put it neutral however, but the key is moving the lever to the neutral position and holding it there until it takes effect.

I'm with you though, why doesn't Toyota come out with a statement telling owners what to do in case it happens? Maybe they woud look like they are admitting guilt if they make such a statement.

I don't know about all of this. I have an 06 Prius and an 08 Prius. I have been a staunch supporter of the Prius and never had any problems. But I also have 2 kids that we take to school everyday and I'm worried this is going to happen to us.

If it does happen, we have practiced what to do. But when you're about to run into the back of someone or plow through a red light, will we remember what to do in a state of panic. I'm pretty concerned about all of this.

 

"..we have practiced what to do..."

 

On the Prius you can move the lever to N for 2 seconds, or you can press the Park button (no need to hold) or you can move the lever to R (no need to wait). Above 10 MPH the car will not go into park or reverse, but will immediately go into neutral.
First, the guy in CA was a fraud. His computer showed that he repeatedly applied the gas, then brake, then gas, then brake, etc. I hope he gets the book thrown at him.

Second, at 90 MPH, there is NO need for power steering! Once the car is moving along, minimal assist is needed to turn the wheel. Power brakes is another story, however!
Having fewer than 100 complaints total, with many of the complaints no more relevant than the CA fraud (some are simply ignorant), concerning over 10 million cars over a three year period (representing BILLIONS of miles driven), I think you would be more reasonable to worry about getting hit by lightning, or a thousand other things that aren't going to happen. Even if there were 100 deaths from this problem, it would still be less likely than winning the PowerBall lottery.

-- Alan

 

And how many of us would be buying a lottery ticket if "winning" meant certain injury or even death..??

 

http://pressroom.toyota.com/pr/tms/d...tration_1_.pdf

From Exponents document, above...

"..Figure 1. A 200 ohm resistor is apparently placed between the output signals of the two pedal position sensors...."

Note the word "apparently"....??!!

I had assumed that the "short" Dr. Gilbert placed across the two sensor signals had just enough resistance, accidental and unintentionally, that a voltage difference greater than the monitoring system was checking for, 0.020 volts (only 20 millivolts), remained between the two signals.

I think that what Exponent is saying here is that in order to replicate Dr. Gilbert's experiment BUT NOT trigger the monitor they had to use a 200 ohm "short" between the two sensors. 200 ohms is well above any accidental or unintentional resistance I would have assumed.

Given that the two sensor output voltages should ALWAYS be displaced by at least 0.80 volts (factory document), using a difference voltage as low as 20 millivolts is unreasonable if one wishes to truly detect short between the two sensors.

Apparently (there's that word again) Exponent assumed a 200 ohm short since that's the resistance they had to use in order to NOT to trigger the firmware monitoring test.

From Exponent, again.

"..To bypass setting the DTC code on the 2007 Camry Exponent slightly modified the parameters of Dr. Gilbert's demonstration...."

"...By carefully engineering the modification.."

Carefully engineering the modification...

Yes, using empirical engineering methods to select a shorting resistance that provided "just enough" signal shorting to still allow a voltage difference above the detection threshold.

In other words the 200 ohm resistor wasn't small enough, low enough in resistance, to "fool" the 2007 Camry's firmware sensor monitoring system, so Exponent chose another value.

First they "ASSUME" Dr. gilbert used a 200 ohm resistor with absolutely no evidence of that (granted, either way), now they modify their own assumption to fit the new case.

And yes, you can "short" the two signals together with just enough resistance to still remain above the minimum voltage difference detectable by the monitoring firmware. And now, if you wish, provided you carefully select the resistance of the "short", connect the one sensor to the 5 volt reference to create a runaway engine "without" setting a DTC.

Or, if you like, you could short the one sensor to a reference voltage right at the maximum of the normal operating range, the engine would go WOT, but no DTC would be set.

"...Exponent was able to rewire the pedal sensors and achieve engine revving without setting a DTC...."

Yes, so could anyone, by empirically selecting the shorting resistance.

And finally:

"...Exponent also evaluated how vehicles made by other manufacturers would respond to the same rewiring that Dr. Gilbert showed in his demonstration. Every vehicle from other manufacturers tested by Exponent could be induced to respond with a sudden increase in engine speed and power output, although the parameters of the rewiring changed slightly from vehicle to vehicle. These demonstrations in no way indicate a defect with any of the vehicles tested (including the Toyota and Camry)..."

...although the parameters of the rewiring changed slightly...

NO SHxx, SHINOLA..!!

....no way indicate a defect with any of the vehicles...

Avoiding a public REBUTTAL by other manufacturers, "this".

But I still find myself puzzled that this worked, so far...

 

Can you provide a reference link to this correction? I have not seen it yet.

Quote:

Note that it says "throttle", no mention of the gas pedal position whatsoever.

Without having seen Toyota's correction, I have no idea what the context of "throttle" is. It is entirely possible that the throttle is left fully open when the fuel is cut off such that the throttle position being open could be consistent with a varying gas pedal position in this drive-by-wire system. Or, throttle could be synonymous with gas pedal in the context used.

Neither the PSD torque nor the brakes (when applied evenly to both wheels as when functioning normally) will induce a significant net steering torque on the steering wheel. There will be some "torque steer", but going straight at high speed is not going to see much of that. It will be maximum when turning (left and right wheels at different speeds), and any more than minimal turning is not possible at high speeds unless the car is out of control (from a steering perspective).

I was not talking about irrational behavior, but about applying a rational perspective on the issue. Buying lottery tickets has little to do with rational behavior! Also, of the hundred or so UA complaints against Toyota in the last 3 years, only a small percentage have involved any injury or death (unless you count fear and an adrenalin rush as injury!).

-- Alan