DIY brake questions for DIYers.

The only reason you would need to remove brake fluid before pushing the caliper piston back would be if someone had (unnecessarily) added brake fluid in the past. Picture this: the car starts out with full thickness brake pads, and brake fluid level near top of optimum range in the reservoir. As brake pads wear, pad thickness reduces, and accordingly brake fluid level drops in the reservoir. As long as you do nothing about this, when it comes times for new brake pads, and you push the pistons back, there is no danger of overflowing.

Even if brake fluid may have been added (overzealous DIY'r or service department), I would just monitor level in the reservoir when pushing the pistons back, baste a bit off, if and when the level goes above the high mark. Note: in a properly functioning brake system without leaks, there's never any need to top up the fluid.

One further caveat: your Prius likely has plastic pistons (if it's similar to third gen), so be very careful when pushing them back, apply full even bearing, say place a plywood scrap across the full face of piston, push on that, with a C-clamp or whatever.

Further: some recommend to open the bleed screw when pushing the caliper back, so that the fluid pushed back goes out instead of up the lines. I've never bothered with this, and never had any problems. Bleeding brakes on Prius is tricky; the car should be in "invalid mode" so this is likely best avoided. A periodic (3 year or 30K mile) brake fluid change is a good idea (recommended now by Toyota Canada): doing this more-or-less negates the arguments for opening bleed screw during piston push back, the fluid is in good condition.

There's no need to remove the cap; the system's not that air-tight.

BTW, is your Prius a 2016? That's generation four, not two. Some mix-up??

 

Although I have not yet had the joy of doing a brake job on my 2007, there are some habits I've developed over the years from previous vehicles. Here's an important one for any vehicles that have ABS. DO NOT push fluid back into the system. Connect a small plastic tube to the vent/bleeder fitting, rotate it 1/4 turn and then push the caliper piston back in. Let the fluid push out the plastic tube into a bottle then tighten the bleeder fitting. This will prevent any system wear particles from pushing back into the system. Once you've done all four brakes, just add fresh fluid to the reservoir.

The last thing in the world you need is for any junk to push back into the ABS actuator and cause something to lock down. I'm sure there are plenty of guys here with more brake experience than me, so hopefully they chime in.

 

Remove Motor MTR relays just in case the actuator motor wants to accidentally turn on. But with the 12V aux battery hooked up you may get codes. So disconnect 12V aux battery, remove 2 MTR relays because if only one comes out the other will still work (its a redundant), then pump 40 times to get the pressure down and of course keep FOB away but if the 12V is disconnected you will be fine. Want more insurance get some 2x4 that will fit in to caliper after you compress it slowly and install with something like a rubber band to hold it in just in case you brain fart.

 

Not sure about second generation, but with third gen I disconnect the 12 volt negative lead at the outset, and leave it off until done. Last thing I'll do before reconnect is firm up the brake pedal with multiple pushes. What this accomplishes:

1. Avoids chance of system pressurizing while the caliper's off the rotor (which could pop the piston out.
2. Avoids brake computer detecting excess pedal travel, throwing a code.

 

Surprisingly it also says to remove connector to brake fluid reservoir which makes sense. We also do that when bleeding so the Skid control/ Actuator doesnt get confused and set a unnecessary code.

 

1. The reason to remove the motor 1 and 2 relays (located in the main relay/fuse box next to the inverter) even though the 12V battery is disconnected, is because the brake system has a bank of capacitors (located next to the 12V battery) which provide a source of electrical power to the braking system when the 12V battery fails. Of course that source is not going to last very long.

2. If you disconnect the 12V battery, then depress the brake pedal a few times before you start work, you will exhaust the charge in the capacitor bank, then you don't have to worry about the brake system doing anything on its own while the battery remains disconnected.

3. You may benefit from obtaining the factory repair manual info at techinfo.toyota.com so that you can see how the brake fluid replacement procedure is supposed to be done, using Toyota Techstream.

4. Once you figure out how to obtain Techstream, then you can follow that procedure.

 

Some of your questions are very concerning. It is good that you ask after seeing the various youtube hacks. You Tube is good to get an idea of whats involved. But you should never monkey see, monkey do b/c it was on you tube.

Both of your Prius has VSC (Vehicle Stability Control).
Each wheel has a speed sensor which relays wheel speed to the ABS system to manage the brake so the car can brake straight/in controll.

The question should be does the Prius use 4channel, 3channel, or 2channel ABS?
4channel is BEST b/c each wheel is managed independently.
3channel is second best; each front is separate. Rears are managed together.
2channel The fronts are managed together and the rears are managed together.
I am inclined to believe the Prius uses 4channel.​

Applies to Prius too.​

Your BEST reference source is the factory service manual. Why do you not have one? This tells you how to do EVERYTHING and lists all the torque values for all the hardware fasteners (bolts/nuts)! When you pay for the subscription, get it for both cars! Chilton and Haynes is junk compared to the Factory manual.

Get the factory service manual from Toyota's TIS (Technical Information System) via the 2-day subscription ($15). Comprehensive diagnostic trouble shooting tree listed for every code.
Toyota - New Subscription

How to convert CHM to PDF
Toyota TIS download tips | PriusChat​

Techstream software is a MUST! Its the official software written for Toyota and approved by Toyota. This is what all the dealers use. If you have Amazon Prime ($22), you may have to return a few cables before you get a working one. Hit up friends/family in IT, as they will likley have access to obsolete Windows 32bit OS laptops collecting dust. Install possible on a Mac; you will have to do research.

With Techstream, you'll be able to bleed your brakes easily! You should do this for your Gen2.
The Gen2 Prius has about one gallon ofr brake fluid! See post #1 fromGalaxee; former member and Toyota Master Tech. What services you need and what you don't | PriusChat

If working on the rear drums, you will most likley introduce air into the system by moving the brake wheel cylinder piston, unintentionally. The rear spring connecting the two shoes together is a bear to unhook. Maybe mechanics have a special tool to keep the shoes together when unhooking the spring?

Bluetooth readers are too limited and can't read ALL codes, nor can it bleed your brakes. So why buy something half arse?

If you don't have a smart AGM compatible battery charger, get one. Useful to connect this to the car when working on the car for prolonged periods, like bleeding the brakes, as the 12V gets drained. Connection of a charger is listed in the service manual BTW.

 

Except for the first gen, which used 3.

The New Car Features Manual is the place for details like that.

Speaking of the NCF, it has detailed diagrams of the valves and fluid routing inside the actuator.

Now, I happen to be in the "open bleeder, don't squish fluid back" camp. I notice that Mendel, whom I respect, is in the "go ahead and squish it back" camp. I'm only saying what camp I'm personally in; I'm not in any position to bully a reader one way or the other.

But I will suggest this: if you are thinking of using the "squish it back" approach, pull up the diagram of your year's actuator, and figure out where you would be forcing that fluid to go (and whether those valves are even open when all the power is cut; the diagrams show which valves go open when unpowered and which go closed). The details change for every Prius generation.

I joined the "use the bleed screw" camp after the first time I did my Gen 1 brakes, thinking I would just squish them back. I found it nothing like old caliper pistons from my younger days I would just shove back with my thumbs. (I don't think it's because my thumbs are so much weaker now!) To move that Gen 1 piston, I had to use a clamp, and crank it. And not because the piston was rusty, or anything like that.

Afterward, I was curious enough to go back to the New Car Features manual and look up what I had just done. I was able to find the path I must have made the fluid return through, but it took some extended squinting.

The thing was, after I did that job, the brake dragged. I replaced the caliper and it still dragged. Which gave me one of those "oh, poop" moments where I figured one old caliper and the replacement right out of the box shouldn't have the same dragging problem, so had I, in fact, damaged the actuator in some way that was keeping the line slightly pressured?

In the end, it turned out the replacement caliper right out of the box really did have the exact same problem as the one I replaced, and the actuator was fine. But until I finally pinned the problem down, I had to keep possible actuator damage on the list needing to be ruled out, which made more work and more worry, than if I had just opened the bleed screw.

-Chap

 

My preference for using the bleeder/plastic tube is based on actually having an ABS actuator fail after pushing (dirty) fluid back through it. Imagine driving down a 45 mph semi-heavy traffic 4 lane road (2 each way), tapping the brakes lightly as you come up to the crown of a hill (saw brake lights on the car ahead of me as he went over the crown) and then have the brakes stay on. Car came to a stop pretty quick and could have been disastrous. Couldn't get car to move, but eventually just floored it. With one wheel squeeling the entire way, it was able to drag the car into a nearby parking lot. Found the passenger side front and driverside rear wheels locked up. Had no real tools with me, tried what I could to get it working to no avail. Tried pounding the heck out of the brake pedal but that didn't help either. Eventually got them freed up by putting both feet on the brake pedal and pushing as hard as I could while bracing myself against seat. Drove around the parking lot a little and then straight home. Did a bit of research about what may have happened, went through the brakes again and thought everything was good to go. About a month later, the wife and I were coming home on the highway doing about 70 mph. All it took was one jackass cutting off another car a few hundred feet ahead of us and everyone got on the brakes hard. So did I, but this time, the car pulled so hard to the left that it actually went sideways and almost into the concrete wall. This time, only the driverside front and passenger rear brakes actually activated. Replaced the ABS assembly, flushed the brake lines twice and never had a problem again.

I've done a lot of brake jobs, my own cars, family cars, friends, etc. I had always pushed the calipers back in so the fluid went back into the reservoir. Personally, I will never again push fluid from a caliper back into the brake line. New fluid is cheap. Risking a brake failure...not so much. Quite often, I wonder what would have happened if it was my son or wife driving at the time?

Air will not be introduced into the system if a rubber tube is attached. Just position the tube so an inch or more of fluid stays above the fitting.

 

I’m just pushing the piston in (and old fluid back). That’s how Prius manual tells you to do it.
But I’m also changing the brake fluid every other year as Toyota service schedule says.

 

Interesting. The Europe or Finland service schedule lists this.

The USA service schedule for the Gen2 Prius makes no mention of brake fluid flush. However, those who know better, will flush the brake fluid with some regularity.

 

Toyota Canada maintenance schedule (for all vehicles) includes brake fluid change tri-yearly or 30K miles, as of 2012 IIRC.