C1364, 225 and C1365 After ABS Pump Replacement

There is so much labor involved in this repair I don't think anybody should risk putting in a used one. These used ones that are on the marketplace could very well be the broken ones that were replaced.

 

And at this point the used ones are getting much harder to find... However there's a 3rd option that we once thought impossible, which is rebuilding and replacing the seals in your existing pump. There's a guy in Los Angelos who started doing them. Hopefully others will too... Way better than rolling the dice on a used one.

 

You pretty much get what you pay for. The guy that was pushing Chinese made new hybrid batteries on here for $1600, only to have them last less than 3 years. Everyone jumped on the band wagon on this new and cheaper option before knowing its longevity. Horrible investment compared to new Toyota OEM batteries.

 

The only outfit I ever read about here that was offering that service is now, according to a recent report, not strongly promoting it. I had never seen them offer much detail on exactly what they had decided the problem was or how they corrected it on rebuild—which I can understand the commercial reasons for, but which also leaves open a bigger potential for disappointing outcomes than if a process is better disclosed and has more eyeballs on it. It seems, sadly, as if this might have been a case in point.

 

Yes, but if someone with a machine shop can figure this out and reliably rebuild them it would save all of us alot of money and make them alot of money in the process.

 

Are you referring to the one with the cylindrical batteries? I remember telling people at the time not to trust that technology since the aftermarket Honda Civic Hybrid I IMA replacement packs which used it were none too reliable. The company that had the best reputation among that group was BumbleBee batteries. Gone now, they were at some point absorbed by LKQ and now are part of Green Bean.

 

Figure it out, and reliably rebuild them, and give us a sound basis for believing that they have.

The shop offering the service before seemed to want to be trusted with a brake actuator and $550 without disclosing their findings or methods, and I remember my gut feeling that, on those terms, I'd probably still just buy new if I needed one. Sadly, that more recent update leaves me thinking my gut feeling wasn't wrong.

Now, I've been an active proponent here on PriusChat of a fuel-injector restoring service, but a key difference there was that Rich was pretty open about how he did the job, and would send the injectors back with a printout of before-and-after test results. So, his strategy for making a buck didn't depend on keeping secrets and being the only guy who knew how to do it, but only on being open and dependable and good at doing it.

Maybe sooner or later someone will figure out the brake actuator troubles and take that same kind of approach.

 

My ABS is still fine (knock wood) but out of curiosity I have looked to see if there are any aftermarket units, which could be very helpful if/when Toyota stops making 2nd generation ABS units. These would be standalone units which implement ABS functions, but don't talk to the car, not Toyota ABS units which have been rebuilt. Found only three things like that so far:

Bosch unit ($$$, more than $8K), which may or may not work with the existing Prius wheel speed sensors, but otherwise should be relatively straightforward to integrate as it is designed to be adaptable for any car:

ABS M5 Kit | Bosch Motorsport

Reuse of Teves MK60 unit from BMW unit ($), very much roll your own:

$1000 USD Standalone ABS Conversion | High Performance Academy
(This next link is toxic to priuschat post. Remove the space and quotes to access it)
"https ://grassrootsmotorsports.com/forum/grm/standalone-abs-installs-mk60-and-more/248099/page1/"

There is an MK100 ($$$, more than $6300) from Continental, who may have absorbed Teves, but it is specifically for use on race tracks and the manufacturer essentially disavows its use on the road:

Motorsports ABS Kit

None of these are good options. All are going to leave codes set all the time unless somebody builds a small box to plug in and lie to the car about the state of the stock ABS system. The Bosch costs about as much as two ABS replacements with a new Toyota ABS unit, the MK100 nearly as much, so that would just be stupid. The MK60 does not appear to be manufactured anymore, only used units are available. There could be all sorts of problems associated with these old units that we don't know about.

 

This Reddit thread:



claims that the root of the problem is air getting into the lines to the rear brakes. That bleeding (just) the rear brakes is enough to restore operation, and how long that restoration lasts depends on how fast the unit leaks.

That seems a bit odd to me, since I would have expected a corresponding leak of brake fluid. Assuming for the moment that this is the problem on most units, it means there must be an opening somewhere to let air leak into the system. Anyway, that sort of failure could conceivably be repaired by sealing the location where the air is getting in. Admittedly welding a tiny crack shut might be too much for the delicate internals of the device. It would depend where the air is coming in.

Have any of you seen one of the ABS units that were repaired by the fellow who was doing that work? Were there any external changes to it consistent with sealing the unit?

Also, there are pretty severe liability issues when working on this part. If somebody rebuilds a starter for a car and it goes bad, well, that's an inconvenience. If the brakes completely fail at speed, that is something else entirely.

 

What they thought was air was probably nitrogen. The brake accumulator is a bellows inside a can, with brake fluid on one side and pressurized nitrogen on the other. When the pump forces more fluid in, the nitrogen is further compressed, like a spring, providing the pressure on the fluid to work the brakes. It's like the pressure tank in a home water system with a well pump.

If the bellows begins a slow leak, you can get nitrogen bubbles in the fluid, as a kind of mystery (how did these bubbles get in? nothing was opened?!). You can notice bark/quack/honk sounds when you release the pedal after braking, and the squished bubbles re-expand and shove fluid back to the reservoir and make the valves honk like saxophone reeds. The pump will have to run more often, because every time you brake, more fluid has to flow to squeeze the bubbles in the lines, and that more fluid goes back to the reservoir when you release the pedal, so more fluid gets used from the accumulator with every use of the brakes.

You can do a bleed sequence and get the bubbles out and quiet the honking for a while, and the pump won't have to run as often. It'll permanently be running a little more often, though, just because there's permanently less nitrogen behind the bellows where it belongs, making the pump cycles shorter (again like a home water system when there's less air behind the diaphragm). And the slow leak is still there, so you'll eventually have bubbles and quacks again.

There was a run of 2010 accumulators that were especially prone to early bellows leaks, and those got recalled. The better ones aren't especially prone to that, but of course that doesn't mean they can't ever get a slow leak after 15 years and a gazillion cycles of use.

But that seems to be only one problem that can develop. Another, and more common, is when some valve in the actuator no longer seals completely, and pressurized fluid can slowly leak through it back to the reservoir, and the pump has to keep pumping more often to maintain the pressure.

Both conditions have extra-frequent pumping as a symptom, but you can tell the difference. Loss of nitrogen from the accumulator will make the pump run more often, both because you're using more fluid with each use of the brakes, and because the cycles are shorter with less nitrogen behind the bellows. But it won't make the pump run repeatedly when you're not even using the brakes.

If there is an internal valve leak and fluid is always slowly escaping from the accumulator back to the reservoir, the pump can have to run repeatedly to maintain pressure even when you are not using the brakes at all. If that's happening, you've got the internal-leak problem, not (or not only) the escaped-nitrogen problem.

The internal-leak issue seems to be the one more often reported here, or at least the one that more often drives people to replace the parts.

I don't think of the nitrogen-escaping problem as completely benign, though, either. If you have signs of that (like the quack sounds), I do recommend using a bleed sequence to get rid of the bubbles, even though that isn't a lasting fix. Don't just decide to live with the quack sounds.

Unlike a conventional system, this one can still brake pretty well even with some bubbles present. The computer just holds the valves open a bit longer and more fluid flows and squishes the bubbles and makes the target pressure anyway. That can give you a sense of security because the brakes don't seem any different (but for maybe some louder swish noises and quacks). In conventional brakes with bubbles, the pedal would feel spongy, and with enough bubbles, would go to the floor and not stop the car.

But the Prius system does have a fail-safe mode it might go into at unexpected times for unexpected reasons, and in that mode it essentially is conventional brakes. If that happens when you've got enough bubbles in the system, you won't like it.

 

Got it. And the brake accumulator is part of the ABS, so if either section fails one still must replace the whole thing.

Searched around for a picture of the internals of this device and found not much:

Understanding the Toyota Hybrid Braking System - Automotive Tech Info

and this inscrutable 18 seconds for what appears to be a different unit with similar construction:

TikTok - Make Your Day

here is a tear down

looks like a bunch of solenoid driven valves. No idea how those sensors work, probably tiny wires going down from them to a circuit board. If the specs for the rod and cylinder were known, and a leak corresponded to a worn rod or failing solenoid, I suppose one might be able to move those parts from a donor to the one being repaired. If the leak was due to any damage to the cylinder though, that's pretty much the whole game. To fix that one could in theory bore out the cylinder slightly and put in a correspondingly wider rod and (internal diameter) solenoid coil, but where would those come from?

Have not yet found a picture of the inside of the accumulator. Perhaps those could be repaired, but as ChapmanF says, that isn't usually the problem.

 

If you're that curious, you could do a lot worse than look at the whole section on it, pages CH-29 through CH-72 in the 2004 New Car Features manual.

Toyota Service Information and Where To Find It | PriusChat

I'm kind of just now realizing this is a gen 2 thread. Some of what I wrote above (like the iffy 2010 accumulators that got recalled) clearly show I was thinking gen 3. But you're right, in gen 2 there's just one assembly that combines the actuator, pump, and accumulator. (In gen 3 there's one that combines the actuator, master cylinder, booster, and ECU, and a different one with the pump and accumulator.) I also wasn't hearing as much about gen 2 brake issues as about gen 3 for a long time, but I guess even the rather reliable gen 2 systems are getting pretty long in the tooth by now.

If the problem is found to be the accumulator, I remember there is a thread on here somewhere where somebody found a source for a similar accumulator with the right threaded fitting and just replaced it. Unscrewed the old one with pressure in it, if I remember the story right. I would have let the pressure out first.

 

Those codes are for the ACCumulator and Front Right pressure sensor circuits.

Use your Techstream - what do you see for sensor voltages? The accumulator sensor typically goes down to around 3.1V when the ecu turns the pump on, and up to 3.6V for turn off.

The right front should read about the same as the left front. Press on the brake pedal, they should change (go up) the same amount side to side.

Did you perform the complete actuator replacement bleed procedure?

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Looked for a while but couldn't find it. There are a lot of threads with "replace" and/or "accumulator".

 

I think this was one of them: Accumulator replacment c1256 accumulator low pressure | PriusChat

The thread above is just about taking a good accumulator from one Toyota actuator to swap for your bad one. Pretty sure there was also another thread where somebody actually sourced a different accumulator bottle that would fit, from an industrial supplier that makes accumulators. Haven't found that one just now.

 

Thanks.

In that thread bad accumulators are replaced with good ones, and it works for a while - and then the ABS fails in some other way. Seems like every time. Possibly because the bleed procedure wasn't ever used? Anyway, more of an argument for buying a new one than for messing around with random used parts (or parts of used parts).

 

What is the accumulator pressure sensor showing?
When the warnings came on, did you press on the brake pedal the same amount as before? Did the pedal feel the same?

I'm trying to wrap my brain around why 3 of the 4 pressure sensors read so differently.

It's been a while since I bled brakes but I recall that for the rears, you crack a bleeder screw while holding the pedal down. The system should push fluid out continuously until you close the screw.

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