ABS pump curiosity

As far as I know, you've just come the closest to finding out that anyone ever has yet (outside of maybe Toyota or NHTSA).

It is likely to be fluid leaking past an incompletely-seated valve. The NHTSA investigation of the issue for Gen 3 has "valve wear" in the title. The hydraulic diagram surely offers some clues as to which valves would be the most likely suspects, given when the fluid leakage happens (in some cases, even when the brakes are not being used, which is a pretty good alibi for the valves that only see pressure while braking).

Maybe you could start by figuring out which physical valves there are which ones on the diagram, and making a labeled version of your photo....

 

My understanding on a gen3 is nitrogen gets into the brake fluid which extends the pump up period. When my 2012 unit went bad, Techstream was used to flush out the brake fluid. It completely stopped the pump cycling and restored normal operation - for about two days. This tells me it was not electronics, calibrations or sensors.

My hunch is an extremely hard braking incident a few days before initial symptoms may have pushed the issue to fruition.

 

In Gen 3 there are two, absolutely distinct, causes that sometimes get mixed up.

The accumulator does contain a metal bellows with pressurized nitrogen on one side (that's the way it's built in all generations). If that develops a leak, then nitrogen does get over to the wrong side of it, so there's some gas in the brake fluid, and less gas on the other side where it's supposed to be, and the result will be more frequent pump running, just like in a residential well water system when there's not enough air in the pressure tank.

There was a bad batch of accumulators in the first year of Gen 3, covered by recall D0H. The metal bellows inside had been manufactured slightly too small, so it banged on the inside walls of the accumulator while driving, and developed early cracks. (Of course that doesn't mean the non-defective ones can't ever wear out; nothing lasts forever. But the undersized ones failed early.)

That issue can give you extra-frequent pump runs when you use the brakes, but it will never explain an issue where the pressure leaks down continually even when you're not touching the brakes and the pump just continually runs. That is an internal hydraulic fluid leakage, nothing to do with nitrogen from the accumulator.

That hydraulic leakage is what the ZJB and related service campaigns are about. The NHTSA investigation into it was focused on hydraulic valve wear.

 

However the system stopped excessive length pumping after the initial brake flush. The best test for your hypothesis might be one assembly at a time. Even today Toyota installs both parts free under the 10 year 150,000 mile extended support warranty. One would think they would stop replacing the pump if it was a known good in the later models.

 

I suspect that Toyota would only install the one part (on Gen3) IF they could definitively test and prove that the pump was NOT at fault (in a "reasonable" amount of time when each car is at the dealer for the warranty repair).

OR, the engineers and lawyers got together and determined that if the actuator had been internally leaking long enough, then the pump was likely "worn out" and should be replaced. Doing that CYA move is likely cheaper than having a few pumps fail completely and dealing with lawsuits, more recalls, and more bad publicity.

Posted via the PriusChat mobile app.

 

I would think Toyota Corporate's pump cost is less than a repeated dealer labor expense. But the question is root cause. It would be nice if someone would rebuild the master cylinders. At that point the root cause would become public. Maybe it will happen now that the unlimited mile warranty has expired. We are already seeing quite a few shocked owners being presented with a $2400 repair at retail.

 

They are in the New Car Features manual. This wiki page describes various ways to obtain that manual, though I don't offhand know which ways are available in Lagos.

I'm sure there are threads on PriusChat where all four generations' diagrams have been posted over the years. I remember one that was active fairly recently and compared them between Gen 3 and Gen 4.

In the NCF there are many more diagrams; there's one showing the valve positions and fluid flow for every mode of operation of the system.

 

If you look on eBay you'll find a guy that rebuilds these I believe he's in Florida I may be able to find his address he sent me two to play with and see if I could get the change to work I haven't had time to fool with it I have them both sitting here on the floor right out of the box they look like they mess with he tried to explain to me some of the stuff going on inside of the system . He only does the Gen2

 

?

 

Exactly.

All you can do is let it wash over you.

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I'm curious if anyone has put together a better troubleshooting guide for these complex brake systems than the service manual. I'm working on my 2007 CHy. It suffers from frequent pumping. After a good flush (or even just a couple zero-downs), the system was well behaved and only needed a couple pumps to maintain pressure for 5 min+. Even when holding the brakes down steady, there was very little accumulator pressure drop. I've been suspecting an accumulator leak, but wanted to make sure.
The bigger issue is that I completed the fluid flush with a "memory reset" and "linear valve offset" which resulted in a C1345 and C1386 because it is failing to learn. I've repeated many times with the same result. According to the shop manual, the brake ECU should be replaced. I presume this is because there are no accompanying codes for specific failures in the actuator circuits. This does not seam right because the ECU is not showing any other symptoms and others have had these codes and fixed by flushing or replacing the actuator assembly.
I've performed many "active tests" and the results were all within spec: manually opening coils results in wheel pressure readings that are good. When pressing the brake hard, I do notice that the wheel pressures are not equal, side to side, and they do fluctuate up and down a bit, especially when the pump runs. Any experience to the root cause and if there are any actions I can take before attempting to fix with a new/used actuator assembly? I'm trying to avoid parts-cannoning this thing and I don't want this car to become another beautiful donor car at the scrap yard.

 

1. What is a 2007 CHy? Your profile says 2012 Prius.

2. Did it have lights or codes before the flush?

3. What is a zero-down?

Good practice and better response comes from starting your own thread.

 

Zero-down is allowing all of the fluid from the accumulator to return to the reservoir so that the accumulator pressure is zero. It is mentioned in the manual (and there is a Techstream method for doing it), because the MIN and MAX level lines on the reservoir are positioned for correct reading when the system is zeroed down. The level will always appear a little lower if checked without zeroing down first, because some of the fluid has been pumped into the accumulator.

 

I bought a car for my son (the 2007 Camry Hybrid). My 2012 prius hasn't had these brake issues yet, so I'm new to this issue. I've learned a lot about how it works and how to use the techstream.
I didn't have any lights or codes before, just the frequent pump running. I don't think it was very long before either the pump would burn out or it would throw codes.

 

Yes there is a button you push to zero down the system under the utilities tab I believe.

 

All I can say is that compared to my 06, your Camry is still "broken". Last time I checked, the accumulator pressure sensor voltage would drop by about 30mV over a 20 minute period. I get 2-3 moderate stops before the pump turns on.

If the Camry pump cycles "often" without using the brakes, then there's an internal leak bleeding off pressure. If it only turns the pump on when you step on the pedal (but that happens every apply), then you likely have a failed accumulator.

As far as replacements go, you already have used parts. It's a crapshoot whether another used one will work at all. And failure to relearn the linear valve offset is not an uncommon outcome.

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I've made some progress now. The accumulator will often hold pressure and not budge lower for a long time but while running the linear valves in "active test" mode, I found that the rear-left actuator will often cause that pressure line to slowly increase, even when set to 0A. Other times, it would require .5A to start opening (like the other 3). This means that this valve is not sealing well everytime and, likely, causing the linear offset to fail. I've cycled this valve open and closed a few times without any improvement. Anyone have any luck getting these to start sealing better? I've only found resources to get them to flow better, none to improve sealing.