lost front brakes completely

you will kill yourself driving that thing. just pay for the tow, i don't wanna hear about you getting hurt! the rear brakes are not equipped to stop the car themselves.

 

<div class='quotetop'>QUOTE(statultra @ Oct 29 2007, 02:29 PM) [snapback]532033[/snapback]</div>

A piece of advice before you make a bad situation worse and kill yourself (or someone else). PAY FOR A TOW TRUCK TO GET YOUR CAR TO THE DEALER SAFELY.

 

<div class='quotetop'>QUOTE(statultra @ Oct 29 2007, 01:29 PM) [snapback]532033[/snapback]</div>

Why would CANBus "disable" the front brakes if it sensed low fluid level? That is a Single Point Failure Mode, if the sensor acted up you would lose your front brakes. No, that is not how the system works.

<div class='quotetop'>QUOTE(statultra @ Oct 29 2007, 01:29 PM) [snapback]532033[/snapback]</div>

It really doesn't. But once you Dad had everything apart and applied the brake pedal, you ventured far beyond the point of a Shadetree Mechanic level of repair. Among other things, there are now codes stored for Low Pressure, and for Relay 1@2, among others. It will still try to apply pressure to the front brakes, but with all that air in there, nothing is happening

As a fail safe mode, the Brake Stroke Simulator Valve is also now closed. Please see the attached diagrams for more information

<div class='quotetop'>QUOTE(statultra @ Oct 29 2007, 01:29 PM) [snapback]532033[/snapback]</div>

Please refer to the Adobe Acrobat file I attached in my previous reply. No, you cannot manually bleed the system. What "bleeding solenoids" are you referring to? I'm going to attach a few more files to help illustrate how the Prius braking system is completely unlike conventional power-boosted systems

If you carefully read the Acrobat file I attached previously, you will notice the Toyota dealership diagnostic tool (Either handheld or the newer Panasonic ToughBook version) is required to COMMAND the system to enter the special fluid bleeding procedure.

Once the technician commands the system to enter the special bleeding procedure, that person must follow the on screen prompts TO THE LETTER to get it right. Again, print out the pdf I attached in my first reply, carefully study it, and you will understand that you simply do not have access to the critical component - the THHT - that you need. Eat the towing bill and get it done right.

In contrast, my FJ Cruiser only needs the THHT if I should happen to introduce air into the master cylinder. But the special procedures still apply, such as letting the electric brake boost pump stop running before opening a bleeder valve

<div class='quotetop'>QUOTE(statultra @ Oct 29 2007, 01:29 PM) [snapback]532033[/snapback]</div>

Well, I didn't call your dad a "moron." I'm sure he meant well, but this is a good lesson for all of us. The Prius is unique in so many different ways, one cannot assume anything, especially "tricks" that worked on older cars.

If you're planning on doing any sort of work on a Prius, it's well worth subscribing to the online Toyota shop manuals. An online subscription - even just a one day subscription - is far cheaper than going beyond the point of no return and fubar'ing the car.

If you had first searched this forum for "grinding brakes" or "barking brakes" you will have discovered the complaint is actually a fairly common one. It has to do with the regenerative braking feature, which results in the actual friction brakes hardly being used.

As a result, the rotors can quickly rust, which usually causes the noise you've heard while braking at slow speeds - once the system transitions from regenerative braking to friction brakes. If you live in an area where road salt is applied in winter, the problem is much worse.

The fix is usually very simple: driving at town speeds of say 30-40 mph, move the shift lever into N, and firmly brake. That forces the friction brakes to work, and a few attempts should clean off the rotors. Some of us have to do that every month.

 

<div class='quotetop'>QUOTE(statultra @ Oct 29 2007, 02:29 PM) [snapback]532033[/snapback]</div>

yes, there is a sensor. and no, it can't just disable the front brakes like that. if the fluid is that low, it'll just happen on its own.

there are DTCs that will tell you if the hydraulic pressure is low and what wheel, but not if there is air in the system. that is up to the tech to ensure that the air is all bled out.

no. you NEED the scan tool. i cannot reiterate that enough. it can NOT be done properly without that tool.

if you drove the vehicle in its current condition, which you told us you did, the system has been compromised. there's air in the system. yes, brake fluid pours out. yes, if you wanna know, technically you can in the ABSOLUTE MOST IDEAL conditions bleed the last few inches of brake line. if you don't do it really quickly under THE MOST IDEAL circumstances and you REALLY KNOW WHAT YOU'RE DOING... air WILL GET INTO THAT LINE and YOU WILL HAVE TO GO TO THE DEALER. otherwise you WILL COMPROMISE YOUR OWN SAFETY.

PLEASE PLEASE PLEASE DO NOT TAKE THIS AS YOU CAN BLEED IT YOURSELF. from what you've told us so far, you are WAAAAY beyond the point of being able to DIY. there are a lot of things on this car, as you've seen, that you can DIY. THIS IS NOT ONE OF THEM.

as someone who would be in the position to work on your car, DH would not even drive the car from the lot to his shop bay. he would push it. based on your description.

the first time he and his coworker encountered an open prius brake system, it took both of them 90 minutes to do it right. now, he can do one himself in 20 minutes but only because he's done a bunch of them. a whole bunch. this is not for beginners. i cannot reiterate this enough.

no, sorry, scantool or nothin. look, i know you wanna do this yourself- DH can't stand the thought of anyone else so much as touching our cars- but you're well beyond that point now.

as a general rule, prius or not, brakes are serious stuff. if you're not 100% certain of what you're doing, please don't. this is not playing with the function of the vehicle so much as the inherent safety of it, at this point you're risking the life of the person behind the wheel.

 

<div class='quotetop'>QUOTE(statultra @ Oct 29 2007, 03:34 PM) [snapback]532085[/snapback]</div>

Ah, this shines an entirely new light on the situation. You didn't say anything about a severe frontal impact, nor did you say anything about already having the manuals. Which is odd, as the shop manual clearly warns about the possibility of partial to complete braking failure by not following the detailed instructions

Was the car ever driveable, or did it make a grinding noise from the start? So now it could actually be something making physical contact during braking. Now with all that air in the system, possibly in the solenoids too, the car is essentially undriveable

<div class='quotetop'>QUOTE(statultra @ Oct 29 2007, 03:34 PM) [snapback]532085[/snapback]</div>

I'm a wee bit curious how you managed to get around those "computer problems" without the THHT software. Also very curious about the VVT "oil valve modifications" as this is the first I have heard of it

<div class='quotetop'>QUOTE(statultra @ Oct 29 2007, 03:34 PM) [snapback]532085[/snapback]</div>

Please read the pdf and examine the brake system map again. In fail safe mode, the front brake is NOT isolated from the system, the front brake is fully enabled. The brake stroke simulator is bypassed due to loss of pressure, it is "out of loop" at the K port bypass.

Don't forget, you are dealing with wheel cylinder pressure sensors, the accumulator pressure sensor, and the master cylinder pressure sensor. In essence, only the front brakes are in the loop, in addition to residual pressure possibly available to the rear drum brakes

There are various failure modes available, and the shop manual clearly explains what may enable the various failure modes, their limits, and how to resolve them

<div class='quotetop'>QUOTE(statultra @ Oct 29 2007, 03:34 PM) [snapback]532085[/snapback]</div>

No. You can examine raw CAN data, but the proprietary data/codes and messaging requires THHT software to interface. This issue has come up before with regards to LIN/BEAN messaging.

Using an Agilent 54600 MSO from work, with a Agilent N2758A CAN trigger module, you can look far beyond simple SOF triggers and trigger based on specific messaging format. The neat thing is that I can trigger based on standard 11 bit or extended 16 bit ID's.

It's very helpful when you can trigger on a specific CAN ID by looking at the SPI and comparing it to the actual analog signal input, say a pressure sensor or an RTD sensor. The CAN TRG can look at the trigger pod and contrast to the trigger pulse event.

<div class='quotetop'>QUOTE(statultra @ Oct 29 2007, 03:34 PM) [snapback]532085[/snapback]</div>

No, I'm a systems analyst with 22 years experience in industrial process control, avionics, signals characterization and interception, and telecommunications. The CAN protocol has many overlapping and obvious extensions from automotive, to industrial, and even extensions in avionics past ARINC 429

Thus my fairly easy access to the Agilent MSO. At a very basic level, CAN is the same protocol whether in process, signals, or telecomms. The particular Agilent MSO/trigger I mentioned is really beyond the price range of anybody - unless you've recently won a Powerball lottery.

I'm hoping you realize that the overall complextity of the messaging format all but excludes you from the sort of diagnostics and remediation you have to perform on that Prius. I'm aware that some CAN implementations, such as GM's, are pretty much public domain as you can use an aftermarket OTC Genesys or similar diagnostic tool with appropriate CAN dongle to diagnose GM brand domestic cars/trucks

Unfortunately, I see no such initiative to achieve the same public availability for Asian and German CAN implementations. I am unaware of any "shadetree" trick you can try to remediate the braking problem now

 

<div class='quotetop'>QUOTE(statultra @ Oct 30 2007, 07:53 AM) [snapback]532374[/snapback]</div>

That's cheap. The Agilent MSO with CAN interface is approximately 13 times more expensive.

 

<div class='quotetop'>QUOTE(statultra @ Oct 30 2007, 07:34 AM) [snapback]532409[/snapback]</div>

Ask your friends if they hav AAA. I think it would eliminate another problem...

 

For what it's worth, some aftermarket scantools are starting to get
more hybrid-specific functionality. Brakes may still be one of the
not-quite-there areas, but you might want to poke the support folks
at Autoenginuity or OTC/SPX [Genisys] and see what they could offer.
There are a couple of others but probably not in the running as
far as being able to competently talk to a Prius yet.
.
_H*

 

<div class='quotetop'>QUOTE(statultra @ Oct 30 2007, 08:05 PM) [snapback]532726[/snapback]</div>

It's called TOYOTA DEALER - Do everybody including yourself a favor and TOW the darn car to the dealer.

If you kill yourself - so be it; Killing an innocent passerby is a completely different story -

 

stat, for a generally smart kid you're doing something really, really stupid.

if you drove it, with that piston shot out of the caliper, there is air in the line. you had to depressurize the system? WHY is there pressure in the brake system? the brakes are operated by hydraulic pressure... so if there's pressure in the lines then the brakes are applied... something is not right.

you're asking for trouble. seriously.

 

What part about "take it to the dealer" do you not understand?

You have a lot of very experienced people telling you to do this. You asked for their advice. And you're ignoring it.

Don't come back after your crash and ask for more advice. Because all you're going to hear is "Told you so." (Doofus)

 

<div class='quotetop'>QUOTE(Godiva @ Nov 2 2007, 06:40 PM) [snapback]534191[/snapback]</div>

...when it was raining brains, some people were holding umbrellas