Brake Booster Accumulator Actuator issue?

Renee Thomas · Oct 8, 2021

I just had a nice "Prius chat" with Ken at Dynasty Automotive. He seems very knowledgable about the issue. He said the order of events should be: 1) scan for the code; 2) check the 12 volt battery (the first thing they always do b/c it can cause symptoms people mistake for hybrid-related issues including the booster); 3) proceed with the repair accordingly. He did agree that everything I told him seems to point to the brake booster. I told him I'd have AutoZone scan the codes today and I'd get back with him. His charge is a few hundred higher than Todd's but I'm thinking I should stay in Orlando at this point since it's probably going to cost me a few hundred to get my Prius to Tampa, plus the hassle of doing that, and I'd need a ride, etc.

jerrymildred · Oct 8, 2021

Wow. I wish it would have held up a little longer. A tow to Tampa wold be pretty expensive. And the guy at Dynasty is right to scan for codes before doing anything else and to check the 12V. I had a low 12V once and the only sign it was low was that it took the pump a long time to come to pressure and shut off. But if it's doing that stuff while driving, that's probably not the battery.

Renee Thomas · Oct 8, 2021

jerrymildred said: ↑

Wow. I wish it would have held up a little longer. A tow to Tampa wold be pretty expensive. And the guy at Dynasty is right to scan for codes before doing anything else and to check the 12V. I had a low 12V once and the only sign it was low was that it took the pump a long time to come to pressure and shut off. But if it's doing that stuff while driving, that's probably not the battery.
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Oh, regarding the 12V battery - I forgot to mention something else that happened when the brake booster issue occurred last night. I noticed the air conditioner stopped cooling during the 20 minute ride home. Also, the wipers were running slower and the window was operating slower. I mentioned that to Dynasty Automotive but he still thinks it is likely a failure of the brake booster. How is the 12V battery possibly involved with the brake booster issue, I wonder. I didn't get a code scan today due to a full day obligation but I'll get that done tomorrow and see if it's the brake booster failure code.

ChapmanF · Oct 8, 2021

Renee Thomas said: ↑

the air conditioner stopped cooling during the 20 minute ride home. Also, the wipers were running slower and the window was operating slower.
Click to expand...

If all of that stuff was happening while the car was READY and driving, then you had a shutdown of the DC/DC converter and everything was running off the 12 volt battery for that interval. Among other things, that will make the brake boost pressure a lot slower to come up, possibly slow enough to give you the lights and the long solid beep from time to time (and unassisted brakes).

What that means is not necessarily that you don't have an actuator problem, but that the converter problem may have exacerbated it. Had the converter not shut down, the drive to Tampa might have worked out.

Unclear why your converter would have shut down, but a little electric pump for coolant is a common villain in that story.

Renee Thomas · Oct 8, 2021

ChapmanF said: ↑

If all of that stuff was happening while the car was READY and driving, then you had a shutdown of the DC/DC converter and everything was running off the 12 volt battery for that interval. Among other things, that will make the brake boost pressure a lot slower to come up, possibly slow enough to give you the lights and the long solid beep from time to time (and unassisted brakes).

What that means is not necessarily that you don't have an actuator problem, but that the converter problem may have exacerbated it. Had the converter not shut down, the drive to Tampa might have worked out.

Unclear why your converter would have shut down, but a little electric pump for coolant is a common villain in that story.
Click to expand...

Hmmmm....when you say a common villain is a little electric pump for coolant, it reminds me that my coolant flow control valve is sticking. It has been throwing the P1121 and P1116 code for over 24,000 miles, more than 6 years now. I haven't wanted to spend the $600 since it "unsticks" as much as it "sticks" and it never has been a problem. I must say that I have just noticed in the last few weeks that the "check engine" light doesn't go off at all. When I had the code scan done just a week or so ago (before the brake booster failure last night), it showed the same old codes P1121 and P1116. And I read through my notes last week about those codes again just to be sure and the notes said the purpose of the coolant control valve is to let coolant flow through the heater core and if I don't need the heater, then it won't hurt if I don't replace the part. Are we talking about the same part here?

Renee Thomas · Oct 8, 2021

I also want to mention in October of 2012 (31,500 miles) my 2009 Prius experienced symptoms of a failed Hybrid Electric Water Pump (all of the flashing lights, complete failure of the entire car's operations, we had to push it off the road, etc.) but after sitting a few minutes turned off, I started it and there were no flashing lights or warnings so I took it straight to the dealer. The dealer repair dept. diagnosed it as the "auxiliary battery" (that is the 12V battery, I assume) and I paid $248 for a new battery because the car was just beyond the 3 yr warranty for the battery (by just 5 months, ugh). The service manager mentioned he had seen a service bulletin for an "inverter pump" but the service guy said it was the auxiliary battery. A week later I went through a similar failure (including loss of A/C) but it drove OK so I took it home. That night I researched the heck out of "inverter pump" and found matching symptoms. I brought my car to the dealer the next morning and proposed it could be the "water inverter pump." (Keep in mind, this was all in October of 2012 and the safety recall notice for the Hybrid Electric Water Pump didn't come out until 2013. That safety recall notice mentioned a potential for a short circuit between coil wires inside the motor that could create an open fuse for the electric power supply circuit. If the fuse is open, the hybrid system can stop while the car is being driven and it could increase the risk of a crash. No kidding!) At the dealer in October 2012, after the second failure, the alerts were still showing, and they said it was the "inverter cooling pump" but there was no service bulletin for it and it wasn't under warranty. I was pretty adamant that I believed that was the problem from the start and they had already charged me $248 for a battery I didn't need considering the same problem happened a week after installation of a new battery. So, they agreed not to charge me for a new inverter cooling pump. Then fast forward to January 2013, when I received the safety recall notice for the Hybrid Electric Water Pump which they then replaced in March of 2013 (35,787 miles). I have detailed notes on these events and can provide part numbers, etc. if anyone is interested. Now I'm very curious if someone can confirm if the "inverter cooling pump" is the same part as the "Hybrid Electric Water Pump." I've always thought they were the same part because the symptoms for their failure were the same. After the events of 2012, I never had any problems with my Prius except for the "coolant flow control valve" sticking since 2015 (codes P1121 & P1116)....which brings us to this point in time. Are these all related to my brake booster? When I read about the brake booster failure other people were having, they described the lights, warnings, and same symptoms I experienced last night, but no one mentioned the loss of A/C or slow wipers, or windows. I also want to thank you guys for sharing your knowledge on this subject. I really appreciate it!

ChapmanF · Oct 8, 2021

There are two separate cooling systems under the hood. They both use the same pinkish coolant, but they are not connected to each other. One system is for cooling the engine, and the other is for cooling the inverter (and also the transmission).

The "inverter cooling pump" and the "hybrid electric water pump" are very likely two different people's names for the same animal ... the pump in the cooling system that cools the inverter.

However, your P1121 and P1116 are not related to that system. Those codes are about the coolant control valve in the other cooling system, the one that cools the engine. That's just another problem that you happen to have.

The only connection between these things and the brake system is that the brake system requires electric power, and that comes normally from the DC/DC converter (which is contained in the inverter assembly). If that is not getting cooled enough (maybe because of the little pump), then it shuts off its power output, and when that happens, suddenly the whole car's electrical system is riding on the 12 volt battery, and the wipers slow down, and the windows slow down, and the brake pressure pump runs like a dying windup toy, and all the other stuff that happens when a whole car is trying to run from a battery the size of a lunchbox.

Renee Thomas · Oct 8, 2021

ChapmanF said: ↑

There are two separate cooling systems under the hood. They both use the same pinkish coolant, but they are not connected to each other. One system is for cooling the engine, and the other is for cooling the inverter (and also the transmission).

The "inverter cooling pump" and the "hybrid electric water pump" are very likely two different people's names for the same animal ... the pump in the cooling system that cools the inverter.

However, your P1121 and P1116 are not related to that system. Those codes are about the coolant control valve in the other cooling system, the one that cools the engine. That's just another problem that you happen to have.

The only connection between these things and the brake system is that the brake system requires electric power, and that comes normally from the DC/DC converter (which is contained in the inverter assembly). If that is not getting cooled enough (maybe because of the little pump), then it shuts off its power output, and when that happens, suddenly the whole car's electrical system is riding on the 12 volt battery, and the wipers slow down, and the windows slow down, and the brake pressure pump runs like a dying windup toy, and all the other stuff that happens when a whole car is trying to run from a battery the size of a lunchbox.
Click to expand...

Thank you for continuing to help me understand this. I am great at keeping notes but I don't quite "get it" yet when it comes to last night's problem! Are you saying that it's possible that the loss of my A/C, slowing of wipers/windows last night with the brake booster failure could be a result of another problem with the "little pump" that is contained within the "inverter cooling pump"/"hybrid electric water pump" in that it is not working properly such as to cool the inverter assembly, leading to the electrical problem? Honestly, I don't even know what the "inverter assembly" is! Is the "inverter assembly" something that converts electricity related to the hybrid battery and the 12V battery? Because if the "little pump" is failing and that is a pump contained within the "inverter cooling pump"/"hybrid electric water pump" that I've already had replaced once as a safety recall, then it scares me to death to think that it is the same part that went bad in 2012. If so, that should be another safety recall issue that the dealership should replace at no charge. I shouldn't be paying a mechanic to fix that, agreed?

Also, I've seen the problem I had last night described as a failure of the "brake booster/accumulator/actuator" and I'm wondering if those have something to do with the "little pump" you mention. Could it be possible that all of my problems are originating from the "inverter cooling pump"/"hybrid electric water pump" needing replaced again?

Renee Thomas · Oct 8, 2021

@ChapmanF - I just googled "inverter" and I see that it is indeed an electrical thing...have you seen this article? You have a 2010 Prius! I know where the "inverter" is now - it's that silver box under the hood, lol. I know that the brake booster/accumulator/actuator is tucked in there somewhere....
After second recall, Toyota Prius electrical system is still overheating - Los Angeles Times

ChapmanF · Oct 8, 2021

I do have a 2010 Prius, and I have been paying attention to the recalls involving my inverter. I don't think that LA Times article is a particularly useful source though.

In your Gen 2, the inverter assembly is the big silvery box on the right here, with the snazzy "HYBRID SYNERGY DRIVE" logo. The reservoir that has been circled looks empty in this photo, which is not how yours should look! There should be pinkish coolant filling it up to the F line.

The inverter assembly is an "assembly" because there are several things in that big silvery box. They all have important electrical jobs to do. And that pinkish coolant gets pumped through all of them to keep them all cool. (The pump is not inside that box ... just connected to it by some of those hoses.)

Two of the inside components of the inverter assembly, the beefiest ones, have the job of moving high-voltage electricity between the traction battery in the back and the two motor-generators in the transmission. They can move power in either direction, from the battery to either MG, from either MG to the battery to charge it, or from either MG to the other.

The next beefiest component in there has the job of supplying power to the air conditioning compressor (through the orange cable you can see right there in front).

The last and puniest thing in that assembly is called the DC/DC converter, and its job is to start with the high-voltage DC from the traction battery and MGs, and convert it into 12 volt DC for powering all the rest of the normal car stuff in the car, and keeping the 12 volt battery charged.

Now you can begin to see what happens if those things become overheated. From here in Indiana, I can't give an opinion on why yours might have overheated; the pump is one common culprit, but not the only possible reason.

If the inverters responsible for the MGs overheat and have to shut down, your car becomes stationary. (Generally, they try to go to a reduced-power mode that lets you 'limp' off the highway.)

If the one responsible for the air conditioning compressor has to shut down, you will have no A/C, just warm air blowing from your vents.

If the one responsible for 12 volt DC conversion has to shut down, then suddenly the dinky 12 volt battery in back is having to carry all the car's normal 12 volt car stuff. So the headlights go dim, the wipers slow down, the windows slow down, the brake pump runs slowly, radio reception gets bad, and so on. Everything just gets dimmer and slower and slower and dimmer as the poor 12 volt battery depletes. If you were to try to push ahead long enough, eventually the car would be dark and off.

Often with those "insufficient cooling because of the pump" stories, you can park the car and turn it off and wait for the inverter insides to get nice and cool again, and then you can start it right back up and it's fine (for a while).

The usual check for whether that coolant pump is working is to turn the car ON (two button pushes without the brake), then take the cap off that inverter coolant reservoir and look in at the pink coolant inside. You should definitely see that it is flowing. If it looks like it is standing still, there's your cooling problem.

Renee Thomas · Oct 9, 2021

ChapmanF said: ↑

I do have a 2010 Prius, and I have been paying attention to the recalls involving my inverter. I don't think that LA Times article is a particularly useful source though.

In your Gen 2, the inverter assembly is the big silvery box on the right here, with the snazzy "HYBRID SYNERGY DRIVE" logo. The reservoir that has been circled looks empty in this photo, which is not how yours should look! There should be pinkish coolant filling it up to the F line.

The inverter assembly is an "assembly" because there are several things in that big silvery box. They all have important electrical jobs to do. And that pinkish coolant gets pumped through all of them to keep them all cool. (The pump is not inside that box ... just connected to it by some of those hoses.)

Two of the inside components of the inverter assembly, the beefiest ones, have the job of moving high-voltage electricity between the traction battery in the back and the two motor-generators in the transmission. They can move power in either direction, from the battery to either MG, from either MG to the battery to charge it, or from either MG to the other.

The next beefiest component in there has the job of supplying power to the air conditioning compressor (through the orange cable you can see right there in front).

The last and puniest thing in that assembly is called the DC/DC converter, and its job is to start with the high-voltage DC from the traction battery and MGs, and convert it into 12 volt DC for powering all the rest of the normal car stuff in the car, and keeping the 12 volt battery charged.

Now you can begin to see what happens if those things become overheated. From here in Indiana, I can't give an opinion on why yours might have overheated; the pump is one common culprit, but not the only possible reason.

If the inverters responsible for the MGs overheat and have to shut down, your car becomes stationary. (Generally, they try to go to a reduced-power mode that lets you 'limp' off the highway.)

If the one responsible for the air conditioning compressor has to shut down, you will have no A/C, just warm air blowing from your vents.

If the one responsible for 12 volt DC conversion has to shut down, then suddenly the dinky 12 volt battery in back is having to carry all the car's normal 12 volt car stuff. So the headlights go dim, the wipers slow down, the windows slow down, the brake pump runs slowly, radio reception gets bad, and so on. Everything just gets dimmer and slower and slower and dimmer as the poor 12 volt battery depletes. If you were to try to push ahead long enough, eventually the car would be dark and off.

Often with those "insufficient cooling because of the pump" stories, you can park the car and turn it off and wait for the inverter insides to get nice and cool again, and then you can start it right back up and it's fine (for a while).

The usual check for whether that coolant pump is working is to turn the car ON (two button pushes without the brake), then take the cap off that inverter coolant reservoir and look in at the pink coolant inside. You should definitely see that it is flowing. If it looks like it is standing still, there's your cooling problem.
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Oh, thank you so much! Now I understand! So, I followed the instructions to see if the inverter coolant pump is working. My inverter coolant reservoir has plenty of coolant, just not quite to the F line. And it is NOT flowing. I have attached images. Next stop is AutoZone to see what codes were thrown on Thursday night. It's literally around the corner from my house so hopefully I can get there without any issues. I am keeping the A/C turned off!

ChapmanF · Oct 9, 2021

If the fluid isn't flowing, it could be because the pump is bad, or it could be something keeping power from getting to the pump (problem in its connections or wiring?), or some kind of blockage in the coolant passages.

For a pump that had been replaced a couple times already, a person might start looking for something besides the pump.

On the other hand, if I'm reading your story right, you had one pump fail in late 2012, and it got replaced because of that, but then that pump got replaced in March 2013, not because of any symptoms then, but only as part of a recall.

So your March 2013 pump has already been in there 8½ years. They do wear out and they don't cost a whole lot; maybe there's no need to look too much harder for an explanation.

Renee Thomas · Oct 9, 2021

ChapmanF said: ↑

If the fluid isn't flowing, it could be because the pump is bad, or it could be something keeping power from getting to the pump (problem in its connections or wiring?), or some kind of blockage in the coolant passages.

For a pump that had been replaced a couple times already, a person might start looking for something besides the pump.

On the other hand, if I'm reading your story right, you had one pump fail in late 2012, and it got replaced because of that, but then that pump got replaced in March 2013, not because of any symptoms then, but only as part of a recall.

So your March 2013 pump has already been in there 8½ years. They do wear out and they don't cost a whole lot; maybe there's no need to look too much harder for an explanation.
Click to expand...

Yes, you have that correct. The March 2013 Hybrid Electric Water Pump replacement was done only because of the safety recall. I had no issues after until this past Thursday night (those associated with the brake booster failure, if that is what it is). I just spent some time watching videos and reading comments online about the brake booster failure. At least one person thinks the 12V battery can cause the brake booster problem. I doubt that. I must get the codes at this point to know where to start. If I see the P0A93 code for the "inverter cooling pump"/"hybrid electric water pump," I'm going to the dealer (also across the street) to have a little chat about my previous safety recall/replacement and see if they'll honor that replacement for no charge. If I also have codes for the brake booster/accumulator/actuator (C1256, I believe), then I'll have to decide where next to take it because I'm not giving that dealership $4,500 for that repair.

Renee Thomas · Oct 9, 2021

@ChapmanF - I would also like to mention that several people said just having your brakes bled will fix the "brake booster/accumulator/actuator" problem. They say they had the same exact symptoms (warning lights, no front brakes, etc.) and after bleeding the brakes, they had no other problems. That seems almost too good to be true. I've never had any brake work done in the past. Could I simply have an inverter cooling pump issue and need new brake fluid? Or am I hallucinating? And I can't forget that 12V battery (also 9 years old now). People say they've simply replaced the 12V battery and the problem was solved. Maybe these people had lights come on their dash, but had no constant intervals of buzzing inside the inverter box while driving, lots of buzzing after parking, and barking sounds when pressing the brake pedal, etc.

ChapmanF · Oct 9, 2021

Honestly, little pumps that run every second you have the car turned on for 8½ years wear out. Your inverter cooling pump hasn't blown your AM2 fuse and left the car without ignition power as they described for the C0U recall; it's just done 8½ years of pumping and joined the choir invisible. It's $145 list price, barely over $100 at dealers giving discounts. That's like twelve dollars a year. I would think of it as upkeep on a twelve year old car.

After that's taken care of, yes, there may still be a brake system issue, which will be easier to pin down once the electrical power isn't complicating the picture.

There are a whole bunch of possible codes related to the brake system. It is probably easiest to wait and find out what the codes are, and then think about what needs to be done.

There are some possible conditions with the brake system where I think you may be able to somewhat postpone the inevitable by going through a brake bleed. Folks who say they have "fixed" their problems that way are probably reading a little too much into a happy reprieve.

Essentially the same regarding the 12 volt battery. Having inadequate power can, as you've seen, make the symptoms of a brake issue worse. If so, resolving that problem can make brake symptoms less worse. I would hold off on the victory dance though.

Edit: hmm, I said that $144.63 price was MSRP, but it's actually an all-dealers discount being shown right on the parts.toyota.com page. I haven't seen them do that before. There are still individual dealers discounting it further.

Renee Thomas · Oct 9, 2021

@ChapmanF - thank you so very much. I truly appreciate your insight and the time you took to help me sort out the issues. I am leaving now for AutoZone! (and unlike those who get advice and then never report back what happened, I promise I will!).

Renee Thomas · Oct 9, 2021

@ChapmanF - OK, I went to AutoZone and pulled the codes. The code P0A93 for the Hybrid Electric Water Pump came up along with the old P1116 and P1121 (those are for the coolant control valve for the heater core - unrelated to the current issue). So with the P0A93 code, I went straight to the dealer and tried to convince them to replace it for free. No luck there but they did replace it within a few hours for only $269 total (they didn't charge me for labor). When I got home I could tell they filled the inverter coolant reservoir and I see movement of fluid when I test for it. So now I'm back to Square One: the buzzing continues within the Inverter Assembly (it lasts for 5 to 8 seconds and repeats while I'm driving, then keeps buzzing after I turn off the car) and if I push too hard on the brake pedal, it "barks." The service ticket says they tested the battery and it's "within good operating condition at this time." I'm not sure I believe they did that because I asked the service manager if they check the battery before a repair, he said "no" and that I'd need to pay a diagnostic fee to check the battery. So I said, "Then I'll pass on that." I figured if there was something wrong with the 12V battery, it'll throw a code or act up in the future. At least I can now rule out the Hybrid Electric Water Pump as a future issue. What's next? Should I wait for another "brake" event to occur and just ignore the buzzing?

ChapmanF · Oct 9, 2021

The P0A93 (whenever you see a round thing in a DTC, it is a zero, not a letter O) is no surprise, and I'm not surprised the dealer declined to change a worn out 8½ year old pump for free. $269 doesn't seem like a bad price with labor.

I am quite sure any buzzing that you are hearing is not "within the inverter assembly". You are most likely hearing the pump on the brake actuator, which is mounted on the firewall, behind the inverter assembly. The two parts aren't related (other than the very general relation that the DC/DC converter supplies power, and the brake actuator is one of the car's many things that use power).

If that pump is cycling frequently, and you are getting barking, then replacing that actuator is probably indicated. If it is not currently reporting any brake DTCs, fine, there isn't any need to wait until it does, since it isn't as if you are angling for a warranty replacement or anything. It'll just be a regular job for Ken in Orlando or Todd in Tampa that you pay for.

Fixing the inverter cooling means you might be able to resume the plan of driving to Tampa if you preferred Todd's shop, assuming the converter shutdown is part of what contributed to your bad experience Thursday night.

But if you're thinking of doing that, I think I would drive slowly around the nabe for a while. or find some lightly traveled roads, and confirm that you don't have another brakepocalypse like that night. And choose a route to Tampa that isn't all on crazy-driving highways, if that's possible.

If in any doubt, I would opt for the nearer shop.

vvillovv · Oct 9, 2021

I'm trying to follow along here and what I'm reading seems to me to indicate some misinformation concerning the DTC's P1161 and P1121

Lucky for me I see Chap has already posted above so I can expedite this post.
This torquenew.com thread describes Toyota codes P1161 and P1121 as Trouble codes not to worry about.
3 Trouble Codes To Not Worry About On Your Toyota Prius | Torque News
I thought it odd when I read that these codes are not related to the current issue, so I double checked.

I hope this is more helpful than confusing. Chap?

Renee Thomas · Oct 9, 2021

@vvillovv - thanks so much for the post. Yes, that is another code that is unrelated to my current issue. I've researched that one to death and maybe I'll get it fixed if the hybrid place offers a good price while I'm getting the brake booster/accumulator/actuator replaced!

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