Catastrophic failure, no brakes at 50 MPH

I actually like "no breaks at 50 MPH" much better than "no brakes at 50 MPH".

Because the 12 volt battery does not start the engine, (the High Voltage battery does that) most people have no experience detecting it is low. If you power windows are MUCH faster going up and down in READY than in ACC, your 12 v battery is in trouble. On a Gen 2 like yours there is a screen to test the 12 volt battery: Weird stuff happening? MPGs dropping? Test The Battery | PriusChat

I bet no brakes qualifies as Weird stuff.

 

i hate when that happens. was the break pedal hard to push down, or did it go all the way to the floor?

 

Whew--that's scary! I noticed that when my aux battery was going out, it would sometimes take a second or two after going into "ready" mode for the braking system to energize...that spooked me a bit when backing out of the garage.

The aux battery can often false-test okay just after being driven (surface charge), so it can go undetected at the service department. Glad you're alright.

 

I wouldn't say you're lucky to be alive. Give yourself credit for not panicking and doing all the right things to make a scary situation end well.

Hopefully the dealership will also do the right things to get your car fixed.

 

Thats very odd as even if the ABS pump fails you still have hydraulic brakes even if they are hard to push they still work no matter what.
The car would be a death trap if you lost all brakes when power went out. And that's not the case.

Yours is the first post I have ever seen that states the brakes went out completely.

The Inverter pump recall addressed this "total failure" as one possibility by issuing a recall on that pump because sometimes when it failed it shorted out blowing a fuse that powers the systems.

Has your car had the recall on the Inverter pump replacement performed? Even though my car was not on the vin list as a candidate for the recall the dealer still replaced my pump for free when I had the steering bolt replaced under recall also.

 

This breaks traditional brake issues..

 

I cannot think of anything that would cause this especially a one time occurrence?????? I cannot see a total loss of 12V power causing this because of the backup capacitor bank. It would have to be a loss of 12V pwr plus a loss of capacitor bank power at the same time then, they magically start working again??? very odd.

I'm betting the techs can't figure it out especially if they can't duplicate it.

 

There is no way the brakes just stop working. It is physically impossible unless the hydraulic lines themselves were cut or had giant bubbles in them. The regen braking definitely goes away with an inverter failure. But you have to stand on the brakes to stop the car with no regen brakes and no power assist hydraulic. If you still have brake fluid, you just didn't push hard enough. I know you said you stomped on it, but really people just don't understand what kind of force is required to stop a couple thousand pounds of metal hurdling down the road at highway speeds. When there is no computer or battery to assist in applying that force for you, it is a rude awakening.

Sounds like general inverter failure that happened at a poor location and you just weren't prepared for what any vehicle without power brakes feels like. When the alternator on your VW failed you still had a 12v battery backup to apply power brakes.

 

I sure would like to see a scan of the mechanic's report

 

The OP doesn't drive a Blue Prius right? Not from San Diego?

 

yes I like 2k's post. The brakes really suck in a prius without regen much less with no power in which case would really suck.
But they will work.

Think the brakes are great then get up to 70 mph's and put the car in nuetral and try to stop briskly. Or tow something in a Prius.

 

You will get a new pump no matter the vin. Your dealer must be a real goof. Sure wish I knew where you live but must be a new rule with new posters.

Make sure you don't post your locale so everyone has to guess.

Well, its like we all tell every poster. Make sure you get all the codes the car threw and post them back here with the 3 digit suffix.
XXXX-XXX
Without those its just a game called supposition. Your car threw alot of them. With those we can tell you what's going on usually more accurately then the dealer. Some dealers are awful and will throw part after part at it. Sometimes on your dime. Good times.

 

I'm not sure what originally caused the loss of power, maybe the inverter coolant pump internal short circuit (known to blow a fuse which causes this problem), or perhaps a short circuited 12V battery overloading the DC-DC converter. Whatever the case, let me explain what happened to you after the event.

Immediately after the loss of power you lost regenerative braking, but you still would have had power assisted friction braking for a short time. This power is provided by a brake emergency capacitor supply, which is just for this purpose.

In reality this situation would be very similar to that of a conventional car if you were to shut down the engine completely (as in 0 RPM) and coast in neutral. You'd only get one real shot at stopping on the residual vacuum, and then you'd be completely without power assist. In either case (Prius or conventional car), after this you would still have non power assisted friction braking. And yes this would feel like having almost no brakes at all if you're only familiar with power assist brakes.

Ultimately the problem was to continue to drive the car with a severe fault instead of stopping immediately. I really do understand about wanting to find a safer place to stop though, and to be completely honest I may well have done the same thing.

As above, if you had shut down the engine on the VW and coasted in neutral, you would have found yourself in exactly the same situation.

 

Hello, I had the same issue with my 04 Prius where all the alarms and buzzers and lights came on. I can tell you that it is most likely your 12 volt battery. When this happened to me, the brakes did not work and there was no reserve brake assist (if you will). I was only going 35 mph, but I could not stop the car very easily. Even pressing the brake pedal fully to the floor did very little to stop the car. I am 6'2" and I was unable to properly and fully stop the car. It did eventually come to a stop, but not by it own choice and with the brake pedal to the floor. After setting there for a few moments, I was able to start the car and safely drive back home as the battery did recover. I did check the 12 volt battery outputs as someone here described using the dash monitor.

To make a long story short, I replaced the 12 volt battery with another Toyota battery and have not had these issues and other mpg drops and issues as before. My last Toyota battery lasted 3 years and I am sure that this one will as well. I live in Florida where it get hot and humid and can be extremely hard on batteries. I hope that this helps.

 

I think this explanation might be leaving out the other, more significant, source of stored power in the Prius brake system: the pressurized accumulator pumped full of brake fluid. The accumulator is what's really the source of braking power assist; the capacitor bank is just a stash of electrical power to provide ABS control for a while. When that electrical power is gone, you don't have computerized antilock brakes any more, but you still have hydraulic brakes and they're still power-assisted until all the accumulator pressure is used up.

Even in older cars with vacuum boosters, there was enough stored vacuum to apply the brakes more than once. In my old truck, if you had just turned off the engine, you'd be able to do three or four firm pedal strokes before the vacuum ran out and the pedal got hard.

The Prius accumulator gives you way more than that. In my (Gen 1) manual, whenever they want you to relieve all the accumulator pressure, they say to turn the car off and step on the brake at least forty times. That's an excessive number, of course, to make sure all the pressure's relieved, but the real number is pretty close. In my car with the ignition off, I counted 29 deep strokes of the pedal I was able to do and feel the power assist. The 30th time, the pedal felt hard like a brick.

A surprising fact in the way the hydraulics are designed is that, if all the accumulator pressure is gone, not only is the pedal much harder, but it acts only on the front brakes. (That's a Gen 1 fact anyway; I don't have the Gen 2 manuals here, but I found a diagram of the hydraulic circuit and it looks pretty similar except that Gen 2 added the ability to control all four brakes independently - Gen 1 controls left and right front independently, and both rears as a pair.)

I can think of one, one only, scenario (not involving cut brake lines or the like) that might be interesting to test in a working Prius to see if a no-brakes situation can be generated. The test would be to disable the accumulator pump so assist pressure would be eventually lost, but at the same time prevent the switching solenoids in the actuator from de-energizing (i.e. simulate a stuck-on output from the brake ECU using a jumper to 12V; could also be simulating switching solenoids physically stuck in the energized position).

The switching solenoids are designed so without electrical power they return to the positions where manual hydraulic braking works without any interference in the actuator. So, they should return to those positions any time the ECU detects a problem and drops power to them, or any time the ECU itself has lost power. If for some reason they stayed in the energized positions when no accumulator pressure was available, I'm not sure whether that would prevent the straight hydraulic front wheel braking from working. It would be interesting to find out.

Even if this scenario could be rigged up to cause a no-brakes situation, it would require very bizarre coincidences in real life ... the accumulator pressure would have to have been already depleted (30 or more brake applications since some failure of the pump), but without the ECU detecting it or sounding the ABS alarm, and the switching solenoid circuit would have to be stuck ON (or the valves physically stuck in those positions). Sounds like a lot of things to be b0rked at one time.

-Chap

 

In the beginning of the alarming and buzzing and all lights coming on situation, I did have some braking assist. As I tried to limp my way home, I went 2 blocks and the situation got worse. The power steering did not want to respond, the a/c went out and the ICE was not responding normally and did shut off on me. I believe that my issue got progressively worse as I was trying to drive slowly back to my house at 11 pm and was only about a mile away. I had just driven 30 miles, mostly on the interstate and had just exited and was on the local streets. Even when I tried to pump the brakes to try and build up some pressure, it did not seem to do any good.
This was the only time that this has happened to me in the 8 years and 80 miles (120k total) that I have driven this car.