Problem with rear brakes...No pressure when bleeding

After months of lurking here and buying the Chiltons for this car I've learned there's a few things you cannot do properly without dealer service equipment on this car. This is one. Brake fluid bleeding & replacement absolutely must be done by the dealer as there's a specific tool/computer to bleed the brakes. Its a very involved bake system with computer controlled brake actuators and speed sensors on all wheels etc etc.
My Prius Chiltons says concerning bleeding the brakes:

The vehicle covered in this manual has a complex braking system that requires special equipment and training to safely remove all air from the system. For this reason we do not recommend that you attempt to replace any components that are part of the hydraulic system.

Pick this up. It will help future repairs:
http://www.amazon.com/s/ref=nb_ss_gw?url=search-alias%3Daps&field-keywords=prius+manual&x=20&y=24

 

uh oh.

this alarm, is it an electronic buzzer? you do NOT want to drive the car when it is making that noise, it is dangerous.

now. on to the brake system stuff. you cannot bleed the brakes yourself on a prius. it doesn't have a standard brake system, and to properly get all the air out of the lines you need to flush it with a dealer scan tool to control all the valves that need to open and close.

you will not get pressure in the rear at all. period. ever. the fronts will give you some but not enough to get all the air out of the lines.

seriously, how many miles does this car have, to need all that brake work? is he just doing this because you did this with your last car or are the calipers and cylinders really going bad? what life are you getting out of the brake pads? the car barely uses the friction brakes.

 

forget it
let it go
take it to the dealer to have its brake done.

if your dad insists on wanting to do his own brake job, then go spend the $1300-$1500 for the toyota scan tool / master tech
scan tool. don't forget to log on to toyota's tech info website to download the software cards.

the rear brakes only do 30 % of the braking. the rear brakes come from the factory with only 4mm of brake pad
material. this should easily last 250,000 miles or more. the brakes only really come to play when vehicle speeds reach
under 7 miles per hour. maybe your dad is resting his foot on the brake, or driving with the emergency brake on. maybe
that explains why your brakes are bad????

question:

How does the prius brakes work ? what should i know about the prius braking system before considering doing
my own work?

answer

a) you need a computer to bleed the brakes

b) 95 % of all the brake fluid that the prius uses is pumped to a dead end. this brake fluid's only reason
for being there is to simply provide the driver with the feel of a conventional hydraulic brake pedal

when you press your foot on the brake, an electronic signal is sent to the braking computer, using two springs, it decides whether to spin the electronic motors backwards to create drag, thus slowing down the car, or to actually push that 5 % left of the brake fluid
to the pads to stop the car.

if the braking computer fails, a failsafe engages, and then the brakes act like a conventional car

im considering this thread closed. theres nothing else we can tell you. your going to have to take it to the dealer
or a hybrid shop that has the computers your going to need

95% is just a guess. it could be in reality 99 %

the brake pedal is more or less fake
the brake pedal is more or less a decoration.

 

but again, the car barely uses the friction brakes- they are only used below 7 mph so he should not need to replace brake pads often like in a former vehicle you've owned. sure, the constant stop-and-go can wear them more, but there are average owners with well over 120k miles who have substantial brake pad life remaining.

replacing anything that you can guess may or may not be the problem, honestly, is probably going to end up costing you more than if you had just took it to the dealer for a diagnosis and had them tell you what's wrong. shotgun diy diagnosis is not cheap either. especially when you wind up needing to take it to the dealer anyway in the end.

the alarm is indicative of a failure in the brake power backup system and has nothing to do with the brake pads. if this is the same alarm i am talking about, the brake light on the dash would also be lit up and you really should not be driving it in that situation.

 

Long story short: you are *totally* screwed.

Do NOT drive the car, as the brakes are now completely inoperable! You MUST have the car put onto a flatbed wrecker and towed to a Toyota garage. There, the mechanic will hook up the Panasonic Toughbook scan interface and go to through the proper documented bleed procedure

I have attached the bleed procedure. As you can see, you *must* use the dealer scantool. There are many servicing items with this car that are unique, and "shadetree mechanic" repairs are likely to cause a lot of damage

If you intend to perform any work on your car, please consider a subscription to All Data DIY. For under $20 a year, you can have access to the same servicing information that is provided by Toyota Techinfo

Unfortunately, some lessons are learned the hard way. Just be thankful nobody got hurt. Get it fixed, move on with life, etc.

 

This is how the Prius brake system is supposed to work under normal conditions

 

This is one of the Prius brake failure modes

 

It's possible to replace the brake pads without opening the bleeder screws -- see here. This still requires some extra steps (like removing the ABS relays) that he may not have run into before.

However, as said above it's too late. Only a dealer can straighten it out now.

 

One other little pointer: the Prius has no vacuum booster, as it wouldn't work when the engine was off. The fact that your husband suspected a vacuum booster is a clear indication that he shouldn't be working on the Prius braking system.

Tom

 

Doesn't this car have an electronic brake booster? Used because vacuum won't work as the motor might not be on? The one I hear gently clattering away every time I step on the brakes?

 

You hear the electric boost pump running. My FJ makes the same noise, as it also has electric-assist power brakes.

Toyota has learned a great deal from the Prius and applied it to their other vehicles. For example, despite having electric-assist brakes, 4 wheel 4 channel ABS, 4 wheel traction control, etc, I actually *can* bleed my FJ brakes without a scantool

For reference, I've attached my FJ brake bleed procedure. Compare and contrast the two vehicles, and you will note obvious differences. I only need dealer help if the master cylinder runs dry

 

Compare the break-down of the FJ master cylinder and booster system

 

Compare the FJ brake schematic to the Prius. Of course, since the Prius uses regenerative braking, there is additional complexity due to the need to have "fake" brakes, eg the Stroke Simulator

Otherwise, the FJ has numerous solenoids for each brake. The FJ not only has 4 wheel traction control, but in Low range offroad, you can engage a mode called Active Traction.

If you're rock crawling, or any other situation where one or two wheels are completely off the ground, the brake is applied to that wheel to prevent it from spinning and losing traction.

Again, despite this level of sophistication, the FJ brakes "feel" completely normal. The only issue I have had is a loud squeal/groan when first backing out of the garage, especially if the brakes are wet. A TSB requires replacing the brake pads. This isn't a durability or performance issue, but a noise issue. I haven't had the TSB done and don't intend to.

 

Has anyone tried to turn off the abs system before bleeding the brakes?
Since the system maintains pressure when the vehicle is not in use.

If you decided to try bleed or flush the brakes before looking at manual and your abs light is on, use the instructions on the link below to rest the system. A regular obd2 scanner did not work for the abs system when I tried.

http://priuschat.com/forums/gen-ii-...-not-using-intelligent-tester.html#post972370

 

You need a mastertech or techstream scan tool to bleed the brakes. This guide outlines the procedure:

Art's Automotive - 30K Service, 2nd Generation Prius

 

We have all heard that you need the Toyota Intelligent Tester that costs 1900 dollars and yes we have all read the factory service manual that out lines how to use it to perform services.

BUT

Some of these smaller dealerships probably have only on Intelligent tester, and if someone was to drops it and breaks it, are they going to stop car maintenance until they get another one? Probably not because they will lose business. The mechanics have all the blue prints at there disposal and they will find a way around the system to be able to bleed brakes or do what ever else they have to do.

I propose that if have nothing more that to say then take it to the dealer or buy the Intelligent Tester you stop contributing to this post.


There has to be away around the system. I propose 2 possible solutions.

1) Turn off the ABS system and the electric brake booster and use the two man bleeding method. When I was flushing the brakes on my prius with out disconnecting anything, the front could be flushed with out a problem. But in the rear the car said loosing pressure and turned off the flow of pressure to the rear.

2) If the first method did not work the you figure out where to solenoid valve is and which way the current is going through it. Then take a nine volt batter and or an appropriate power source, and give it current to keep those valves open. Once the system is one you can use the Mighty Vac to pull the break fluid through the system.

If the computer registered an error in the system use this method to clear the engine codes and abs codes: http://priuschat.com/forums/gen-ii-...ar-dtc-when-not-using-intelligent-tester.html

 

The best tool is a solid *understanding* of how the brake system
works, in all power modes that the car can be in.
.
At the very simplest summary level, front bleeding can be done
with the system off and depressurized, and rear bleeding can be
done with the brake system and the car fully powered *up* and
in READY mode. I'm not even going to try and explain why, because
learning why is the job of the DIYer in the first place.
.
At 110K and five years my car isn't even close to needing any
such procedures, though, and more information on that will be
forthcoming.
.
_H*

 

chickscleo,

You are correct in looking to get the brake situation clarified/fixed ASAP.

The matters of random dash lights and the car not shutting off are typical
symptoms of your 12v battery going bad. The battery's service life is ~4
yrs, and you are there. For your peace of mind and consistent starts and
reliable daily use, it would be best to replace it before the cold weather
comes.

"Neither rain nor sleet nor the Prius' 12v battery will keep us from our
appointed rounds..."

This is something that you can research in the background as the brake
issue is worked out. New batteries go for ~$200 installed at the
dealership. An often mentioned alternative for a little less $$ but greater
reliability/life is the Optima yellow top: :thumb:

12 Volt (12v) Toyota Prius Auxilary Battery with installation kit and free shipping