Brake Fluid Loss and Brake TSB's

Until a few months ago, the brake fluid level in my car has not moved. In the past few months, though, my brake fluid level has steadily dropped to below the Min mark. I checked for leaks all over the car and could find none. Since the Prius friction brakes are used so infrequently I was concerned of where the fluid was going. Plus the fact that I have 35k miles and basic warranty is coming to an end.

I just got back from the dealer. The technician checked the car over and also could find no leaks. He topped the fluid back up to the Max mark and said the fluid must have been used by the calipers, etc. I still do not buy this since the Prius pads should not be wearing this fast. At least I have a record of the problem with the dealership for any future issues and the Service Advisor acknowledged this and said he understood.

I have never had another non-hybrid car use this much brake fluid in such a short amount of time. Has anyone else had an issue with brake fluid loss of this magnitude?

I also took the two TSB's on the Front Brake Rattle and the Rear Brake Squeak and asked to have my brakes updated. The Service Advisor appeared annoyed at first and asked did I have an issue. I told him yes, more in cold weather than warm. They have ordered the parts and I will have to return to have the TSB updates.

Dude, I have noticed my fluid level is low too. It is sitting just below the low mark. I have been meaning to have them top it off but just don't want to hassle with it. 26K miles.

Fluid loss should not happen. Dropping below Min due to wear might happen if you were metal-to-metal on all four pads. A lot of times a small leak in a cylinder inside a drum brake will look like this, but there are no drums here. You can try to create a puddle by trying to push (hard) that brake pedal to the floor. If there is a leak, you will meet heavy resistance at a certain point, but maintaining force will cause the pedal to creep slowly towards the firewall. Several pumps like that would cause a noticeable amount of fluid to collect somewhere.

Pushing hard just activates the Hill Assist. I don't think that test would necessarily work on the Gen III with its braking system.

I have no noticeable leaks myself. I wonder if it could because the reservoir is so small that any little amount of wear shows up quickly?

I would be nice if others would chime in on their levels.

seilerts,

I was hoping you would respond. You verified what I thought. I will try to push hard on the brakes and see what happens.

I know I just had the engine undercover off a couple of weekends ago to change the engine and inverter coolant. Everything on the underside was still pristine. I also checked the hydraulic hoses at each wheel brake caliper. No signs of any leaking. I also looked at the engine firewall around the brake accumulator pump, piping, etc. and could not see any signs of brake fluid at all.

Thanks,

Dwight

spiderman,

Same here. When I first noticed it dropping I kept thinking that I would have them check it and top it off the next time I was at the dealer. Then this past weekend I checked and it was below Min. The Service Manual says that some minor drop in level is normal but if the level gets below Min to check for leaks.

I have not had another car drop this much level. The Prius reservoir is about the same size as my wife's 2007 Accord. In four years I have had to add maybe 1/2 inch.

It would be nice to hear from other 2010 owners.

Dwight

Did the tech check your pad thickness?

I've found typically, by the time pads near their minimum thickness, the fluid reservoir will drop from full to low mark. This is with Honda's over the decades, but I would think Toyota's would be similar.

If your pads have barely worn, I'd suspect there's a leak somewhere.

No, I doubt the technician checked the pad thickness. I am taking the car back next week for the brake TSB's. They should be able to get a good look at the brake pads then.

With the disc brakes, you can easily see the pads. There is way too much thickness with only 34K miles to have pad wear, especially Prius brakes.

I tried pushing hard on the brakes while at a stop light. As Spiderman said, you reach the point of activating the Hill Stop Assist and the pedal does not move any further. I did this a few times at the stop light.

When I got home and in park, I was able to press on the brake pedal until it eventually bottomed out on a mechanical stop. I did this several times. The fluid level did not move off of Max and there were no immediate signs of fluid loss.

I will keep an eye on it and continue to push hard on the pedal to see if I can create a leak. The floor where I keep the car is dry so I should be able to see any leaks quickly.

I'm close to Spidey's mileage, but to be honest, I don't recall ever checking the brake fluid level (i know, i know). If I remember, I'll try to do it this weekend since it's almost dark out by the time I get home. I'll have to move the car to a flat surface, because otherwise my driveway is on a slight angle.

Right, hill assist, forgot about that little feature. What happens if you try it with the car turned off? You lose power brakes, but, after a few pumps, you should be directly working the hydraulic system. Anyway, something definitely is not right. I hope the tech can figure it out.

I don't remember where the brake fluid level was when the car was new. I checked it this morning and it's still about 1/2 way between the Max and Min marks when cold with 50K miles of fairly normal brake use (normal for a Prius that is).

As previously discussed the only normal decrease of fluid in the reservoir would be due to the pistons moving to compensate for pad wear. Any other decrease in level would be due to a leak or if brake work were done. If it is leaking you should be able to see it coming out somewhere though.

However this system does use a brake accumulator. Could it be possible for fluid to be leaking from one side of the accumulator to the other without leaking out of the system?

Also be aware that there have been at least two cases (maybe more) or master cylinder failure reported on this site in Gen3 Prius.

No abnormal sign of wear on the brake pad thickness looking from the outside. No leaks to be found, so far. The garage floor is dry as a bone. I had the engine undercover off a couple of weeks ago and still pristine underneath. No leak around the master cylinder or accumulator pump area.

Good question. I do not know the answer to this. No help from the technician.

Thanks. I did not know this. At least I have a service report on record with Toyota for having low brake fluid.

I am taking it back next week when the parts get here to have the Front Brake Rattle and Rear Brake Squeak TSB's completed. With the tires off and calipers pulled hopefully they will see more and have more info for me.

Just remember to give yourself a little extra room to stop until you find the cause. brake failure could be thrilling.

My thoughts exactly I have not lost any braking up to this point but if I were to get a true leak it could happen quickly.

I'm pretty sure our brake fluid level was mid-way between high and low marks when new. It's still there, with 15000 km (about 10000 mi). Kind of odd actually, any other cars we've had the level at the top mark when new.

Just to document here is a shot of my reservoir. It has been like this quite a while now... although I can't remember what the level was when I first got it.

95,000kms (59,000 miles) and no drop in brake fluid level.

Spiderman,

That is exactly where my level was, just below the Min line. What got my attention is how quickly it fell after holding steady for so long.

Thanks,

Dwight

I tried pushing the brake pedal to the floor several times this weekend. In Park you can press hard on the pedal and it will eventually bottom out at what feels like a mechanical stop. Brake fluid is still at the Max line and no obvious fluid leaks to be found.

I will see what the technician says after installing the brake upgrades this week and post.