2001 prius brake problem. Pedal goes to floor.

Sounds like a leak in the brake system. Dangerous to drive. Get this fixed ASAP and don't drive it until its fixed.

 

Sounds like a bad master cylinder to me. i would sit in the car put some cardboard under it and hit the brakes hard and hold them, if the pedal goes slowly to the floor. get out and check for leaks under the car, do this twice. if there is no fluid under the car, than I would suspect a bad master cylinder. but first get two or three big bottles of dot 3 brake fluid. and bleed the brakes well. its very easy on these cars because of the brake accumulator pump. someone can turn the car to on not ready and just hold the brake pedal down and you should hear the pump come on. open up the bleeder valve and let the fluid come out. do this up front then try the brakes. if a no go, bleed the back ones, if it still dont work. than i suspect a bad master cylinder.

 

Not correct and Dustin, you're mechanic is right and I want to stress to you again the pitfalls of messing with brakes. Its comparable to buying a $20 motorcycle helmet to save money. How much is your head worth?

If you do what you outlined above, you will simply let more fluid out of the system (causing more problems). If your pedal goes to the floor, something caused that. There is no way we can troubleshoot it from here. It may not be low on fluid but, there is air in the lines. Changing pads/shoes is one thing but fixing a highly complicated regenerative/anti lock braking system is quite another.

Even if you do figure out some way to bleed the brakes (which I'm sure is possible), you still have the problem of what caused this in the first place. I am a hardcore DIYer but in this case, I would have to recommend the dealer.

 

A few questions:

- Have the car and the brakes been working fine for an extended period prior to this problem occurring?
- Did anything (like an accident) happen to provoke the problem?
- DTC C1202 is indicative of low brake fluid level. Exactly where is the brake fluid level compared to the MAX and MIN markings on the brake fluid reservoir?
- How do you know that there is no fluid leak? Have you inspected the brake actuator assembly on the firewall, the brake lines leading from the actuator to the four wheel cylinders, and removed the wheels and rear brake drums so that you can look at the front calipers and the rear wheel cylinders?

I have itemized the fluid flush procedure below, applicable only to NHW11 (Classic) Prius. Obviously this procedure will not help if there actually exists a failed brake system component. You first need to figure out where the failure is and fix it. If the problem is other than a leaky caliper or wheel cylinder, you will need to seek professional help.

Regarding the fluid flush procedure, first suck out most of the old fluid in the reservoir with a clean dry suction bulb. Don't go overboard to the point where air can enter the system via the reservoir. Then fill with fresh DOT3 fluid.

Typically you would start with the rear wheels first since the brake lines to the rear are longer. You need a helper sitting in the driver's seat. Make the car IG-ON. Have the helper very gently depress the brake pedal a tiny amount. Do not pump the pedal. Then attach a clear vinyl tube to the right rear wheel cylinder valve, crack the valve open, let fluid run down the tube into a glass jar for collection. Close the valve before your helper releases the brake pedal.

Make sure you keep the brake fluid reservoir full of fluid during this process. If you allow air to enter the system then you will need to seek professional help.

Repeat process with the left rear, then move to right front, and finally left front.
Good luck.

 

I googled this whenI replaced the right caliper I think it came from Priusonline. and I was told what I wrote above. to have my helper turn the car to on, hold the pedal and the fluid will just come out when i crack open the bleeder and will continue to until it either runs out of fluid or i close the bleeder due to the brake pump. I did this after replacing the caliper by starting with the rear brakes and the car was better stopping. Did I do this wrong?

 

As long as the you never let the reservoir run out of brake fluid, you didn't do it wrong. But in passing the same instructions along to others we need to be clear what the stakes are: make sure not to ever let it bleed "until it ... runs out of fluid" because if any air gets drawn in at the reservoir, the DIY part of your project is done. The bleeding required if that happens can't officially be done without the Toyota scantool to work all the necessary actuator valves in the necessary sequence.

(In a Gen 1, I think there might be a way to make that happen without the scantool if absolutely necessary; looking at the fluid diagram in the New Car Features Manual and the circuit details in the Wiring Diagram Manual, it looks as though not too many valves need be involved and it might not be too hard to make it work with some temporary wiring. I've never tried it, and I'd hope anybody wanting to try it would obtain and study both manuals first. And only the Gen 1 is that simple; getting air in a Gen 2 or later would be a worse day all around.)

-Chap

 

That could be a possibility. Or could you have gotten air in it when you replaced that brake resevoir hose. Could be a possible relay, going out. What I would do is see if there is a shop around with a scanner to get into the prius. You could also try looking up luscious garage and shooting then an email. They are in california. But they specialize in hybrids and may be able to give you an idea as to what it could be. Then up can trouble shoot from there.

Guys, what about the scanguage 2. Can that access his brake system?

 

If it can, I don't think vincent1449p has worked out the correct addresses and encodings yet. But there's always the no-scanner, fallback route: use a jumper wire to connect the TC and CG pins (13 and 4) at the OBD-II connector under the dash, turn the key ON, and watch the blinking ABS light. It will blink out one or more two-digit codes (e.g. blink blink pause blink blink blink would be 23) with a longer pause between codes. When it cycles around and blinks a code you've already written down, you know you've got the list.

Correspondence between these two-digit codes and the five-character codes you'd see on an OBD-II scanner is given in the manual, volume 1 (which is also where to find what the codes mean, anyway).

-Chap

 

If the parking brake is released and the drum still won't budge off the hub, the bolt needed to thread into the drum to separate it from the hub is an M8x1.25 thread. I needed to do that the first time I had the drums off after buying the car at 125,000, but I've never needed to since.

-Chap

 

could it possibly be a faulty abs/ brake computer?, see its intermittent, that's what gets me. But it could possibly Be a bad cpu. I had a big diesel truck at the shop I worked at come in and would intermittently just quit, misfir our lose power.Never set codes though. I replaced the ecu. Truck was fine. But this is I prius. I know that. But the truth is, like any car or truck the ecu computers can go out, rare, but it happens. Don't know if this is or case or not.

 

Maybe try to take it to the dealer or one that knows the prius and have then do a brake fluid exchange, maybe something is stuck from old fluid, maybe somehow there is an air bubble in the system. Could be an abs wheel sensor too

 

Hi Dustin, if it's doing the sinking pedal thing with no external leaks, it's almost always a bad master cylinder.
Maybe you can get an aftermarket one, looks like Toyota's really proud of theirs. The key is that when you press the pedal hard it's firmer, if it were an external leak that would make it worse. Hope this helps, and good luck.
(ps, I've replaced maybe 60 or more for the exact same symtom ...mostly Honda's, I'm a new Prius guy). But every one fixed the problem.

 

I don't know a tech there, but if you can change the rubber line leading to it and that other stuff you mentioned, you can probably change the MC. It really is nothing to be scared of if you just don't let it go empty during the process. You want to rig a temp reservoir some how and bench-bleed the new MC before installing. Once you have it bled to some degree, try to put it on without loseing too much fluid/ admitting too much air. Then finger+ tighten the lines, and bleed each line at MC a couple of times just like bleeding a caliper (i.e, don't let your helper release the pedal 'til you tighten the line). You may even find that it seems to work ok after final tightening of the lines and stuff at this point, even though proper procedure says bleed the whole system. You'll also get out any remaining nasty /corrosive/ wet fluid if you bleed a couple cans of fluid through it using all 4 corners. The new, clean,dry fluid is your best defense against any more hydraulic issues. Again, the bleeding process may get to shop level if it does get air into it. But that's far from a sure thing. The only things people tend to do wrong here, would be adjust the pushrod to remove slack (bad idea), and use old fluid grandpa had left over. If you decide to do it, best of luck. I'll try to check back and see how it goes, but not too good about going on line after spending all day there at work (computer boy now after retiring from cars... not sure it's a promotion lol).
And the other thing is, as you've found out, paying somebody for it is no guarantee your diagnosis will be any more accurate than your own, or one like mine... it'll just cost more.