c1364/243- with code, spongey brakes. clear code, brakes just fine

Maybe the flash flooding is a clue so go around the car or at least the sensor that's mentioned in the code go to that wheel pull out that sensor as a 10 mm bolt that holds it into the hub so it can see the tone ring which in the front is attached to your drive axle passing through the hub in the back It's built into your hub bearing so you can't see anything and the sensor wouldn't generally be dirty I'm not sure if it got wet and it was compromised and water got in it that might cause a problem If you know this to be the case by looking at the back of the rear wheel bearing where the plug goes if that plastic is any kind of compromised and it looks like it can take on water maybe spray some wire dryer WD-40 something like that in there until it starts to run out maybe pushing some water out with it and then that will dry and should put you back to hopefully where you were if it's in the front the code then you can pull the sensor out of the hub make sure there's not anything blocking the sensor from hearing or seeing the tone ring dirt something a cigarette butt from the flash flood you know I don't know. I guess just check it out real good.

 

This is about the RR brake fluid pressure sensor, not the wheel speed sensor.

The pressure sensor is located in the brake actuator. The signal gets from there to the skid ECU on the wire between connector A2 pin 41 and connector S10 pin 31. That should make a good low-resistance connection (less than 1 Ω) between those two pins, and high resistance (at least 10kΩ, usually a lot more) to ground or anywhere else.

How high did the water get on the car? Did it get in the cabin?

I would certainly check out the wiring connections before assuming the actual sensor in the actuator went bad.

 

What code(s) are you getting after you clear the codes.

 

not putting away the popcorn just yet

 

I'll give you a left field possibility. If you don't use your park brake and it hasn't been used for many 1000's of miles, then your rear drums could be out of adjustment. I've had brake boost drop because of this. The park brake auto-adjusts mechanically the rear drums to keep them close to the drum as the shoes wear over time. Too far out of adjustment and the car senses low hydraulic pressure and pops a code as it cuts out brake boost.

 

That's interesting I do understand the logic behind that thinking. But considering I haven't used the parking brake in any of the three Prius here the whole time we've owned them except to use the brake bleeding procedures in the Toyota software it requires you to set the parking brake and a few other conditions other than that we've never used the parking brake and then one or two of these cars I'm pretty sure the other people never used it either usually I can look at the pedals and tell what's going on with people's feet that's one of the first things I look at when I look at a car. And I wouldn't think with the rear brakes on the Prius being operated by a somewhat independent hydraulic pump that a few thousands of an inch of extra travel of the rear shoes I would think would make absolutely zero difference to that fluid that's flying through there at decent pressure and plenty of it that pump would be able to pump the whole reservoir full of fluid back to those wheel cylinders if that's what it required Not that that would be good.

 

Sure, that is what happens if the adjustment is neglected. As the actuator only has to hold a valve open until the sensed brake line pressure reaches the target, it just holds the valve open a bit longer if the shoe clearance is too wide. Sometime you can hear an extra-noticeable whoosh of fluid. If it takes too long the system will set a code and never open the valve to that brake line again, to conserve fluid in case there is a leak.

As for the few thousandths, each click of the starwheel is worth 0.03 mm of shoe clearance, a little more than one thousandth of an inch, so that also is the normal adjusted clearance (when it gets wider than that, the adjuster will click). So depending on how long the adjustment has been neglected: if it's been long enough for one click of adjustment to be missed, it takes twice the normal amount of fluid to apply the brakes. If long enough for two clicks to be missed, it takes three times the normal amount of fluid. And so on. If it has been long enough to be several clicks behind, that's a bunch of extra fluid.

I'm not sure what the ECU's threshold is before it says "oop, valve open too long, some problem with that line."

Well, in sum, for the Prius models that have rear drum brakes, regular use of the parking brake is what the rear drum brake adjusters depend on.

There probably isn't any aspect of car maintenance at all that you can't find somebody to post about completely neglecting and still being happy. But PriusChat also serves readers wanting to know how to take care of the car.

 

Well, I did have a hydraulic fault and lose boost in the brakes. All pads/shoes were well worn and the rear shoes were out of adjustment. Replacing all surfaces and adjusting the shoes cleared it up without any code reader. Maybe it just takes extremes of all surface wear and mal-adjustment together to create what I encountered...

 

Oh I keep my drum brakes adjusted Don't get me wrong I have a break spoon in the little back tool panel opposite where the battery is on the other side anytime I'm putting on new tires and all of that nonsense I give them a couple clicks always can feel the slight drag when I rotate the wheel assembly as I'm putting the wheel back on I need to get the disc brake thing sorted out for the rear one or two of these generation twos but who knows when I'll get around to it.

 

They adjust themselves, if you just use the parking brake routinely.

But if you've been doing it manually with a brake spoon now and then, then your post about "we've never used the parking brake and then one or two of these cars I'm pretty sure the other people never used it either" is even more misleading to an unwary reader than it seemed to be at first, since that post didn't mention you had been going in there with brake spoons to make up for the auto adjustment that wasn't happening.

 

I I haven't used them ever that I remember and a memory still pretty good. Except for making all the prerequisites to bleed the brakes just a few months ago a few weeks ago on the other one but anytime I'm putting tires on and whatnot as I'm taking the wheels off to roll them into the tire guy I know how easy the back wheels spin round and round and round and then I just grab my spoon and make two clicks so now they don't go round and round and round so fast and so much there's a slight drag that's how we've always had the drum set on all of those kind of brakes since I don't know the '60s and on most of those cars I didn't really use the parking brake either I remember one time in the '80s one of the dealership people in the back told me yeah you should when you're going backwards just pull up on the brake lever it'll make the adjusters work longer more of a stroke or something tried it once and never did it again I don't think.