Brake troubleshooting

Discussion in 'Gen 2 Prius Technical Discussion' started by punatic, Oct 1, 2021.

  1. punatic

    punatic New Member

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    I have the brake warning light illuminated. Jumpered the OBDI and got codes 41,43 and 44 which according to the Bentleys manual I purchased is the increasing pressure solenoid RL. Did the brake pump 8 times withing 5 seconds, and the light was out for one drive cycle, then back on, so I probably have a real issue. So now reading up on this really cool system, I determined there are pressure solenoid in the brake actuator. Also it answers a question I had, as when I replaced the pads and rotors (before I got the manual), I noticed that the reservoir volume did not increase when I shoved the pistons back. I'm guessing that I shoved fluid into the accumulator, and this may be the reason I have a light. So you folks with some experience...can I release the pressure from the accumulator without needed to bleed the system after, or, that not being possible, can I either swap solenoids and see if the problem swaps, or if not that can I install another solenoid without bleeding? This manual does not give any help with this, I don't even know the location of the accumulator or the brake actuator! Also I observed that the pedal is very firm, and the car seems to brake extremely well, maybe too well! LOL
     
  2. ChapmanF

    ChapmanF Senior Member

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    Nah, you weren't shoving fluid back into the accumulator (unless shoving fluid into a 2000 psi can is one of your superpowers). When returning from the wheel cylinders it goes back to the reservoir; it's just the electric pump that takes it from there to the accumulator.

    I'm too far from Hawaii to ell you what did happen when you shoved the pistons back, but there's another explanation out there. :)

    Some people will open bleed valves when shoving pistons back, just to avoid shoving old possibly-mucky fluid back up into the really cool system.

    Couple things here. First, when getting the brake system's blink codes, you need to keep track of which light blinked each code, because the blinks on the ABS light, the VSC light, and the ECB / ((!)) light are found in different tables in the (real) manual, and some of the numbers can overlap.

    Second, one of the biggest favors you can probably do yourself is to accidentally forget where you left that Bentleys, and get yourself access to the real manuals for the car (more info).

    I am guessing that your 41 was blinked on the ECB light (well, ((!)) is what it might look like), which would make it a C1241 code, which is an issue with the power source voltage arriving at the skid ECU. If you had a scan tool, then beyond the blink code, you could get one of four different INF codes to go with it, breaking it into four different possibilities. The first two are mirror images: the ECU is split inside into twin redundant systems, so the conditions in the first two cases are the same (say, voltage below 8.9 for a few seconds, or the regulated internal 5V went out of spec for a few hundredths of a second), except for happening to System 1 or to System 2. The other two cases indicate issues with the backup brake power capacitors in the back of the car, or maybe the relays bringing power to the system.

    You'll notice there's nothing about C1241 that indicates a problem with the 12 volt battery specifically; the code has to do with power getting to the brake components up front, so all the connectors and wiring on the path can be on the suspect list.

    On the other hand, seeing a C1241 code can be viewed as a very good reason to check the condition of the 12 volt battery before looking very hard for whatever else could have caused it.

    The 43 and 44 codes are two of those cases that overlap. If you saw them on the ABS light, they'd be C1243 and C1244, which both have to do with communication to the accelerometer sensor. If you saw them on the ((!)) light, they are the codes C1377 and C1378, and have to do with communicating with the backup power capacitors in the back of the car ... that could be a tie-in to one of the possible causes of your C1241.

    So from this you can see a few things:

    • None of these codes had the least little thing to do with "increasing pressure solenoid RL", which goes to show how much the Bentleys manual helped you here.
    • They are more electrical in nature, and they might (depending on which lights blinked) cast some suspicion on the capacitor box or the wiring to it.
    • It's important to write down blink codes by which light blinked them, and it's important to have a way of looking in the real repair manual to avoid going on goose chases.
    • All of that ideally comes before rushing into taking expensive actuators apart because of hunches.

    In the repair manual, the C1241 code has an eight page troubleshooting section to help you pin down what caused it.

    If your other codes were C1377 and C1378, those have six-page and four-page workup sections.

    If they were C1243 and C1244, there's a five page troubleshooting section those codes share.
     
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  3. punatic

    punatic New Member

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    Wow, thanks so much for the detailed explanation of this. I really think this is an amazing little car, and I've owned well over 100 cars in my life. The explanation of the brake system I read in the Bentleys Manual showed me the complexity of the system. Anyway I will get the real manual, and I do have some additional info as well as i did watch the blinking lights for some time to get straight what they were flashing

    ABS : 42
    VSC: 45
    I have a brand new yellow top battery in the car, but reading your reply I think I should go and check the connections at the backup capacitor box. I run heavy equipment here on my little farm and am constantly dealing with connection issues due to the moisture. I'll look at the box tomorow...and I'll order a real manual now...Thanks again!
     
  4. ChapmanF

    ChapmanF Senior Member

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    Those two extra codes are just the ABS saying "you have ECB codes, go look at those", and the VSC saying "you have ECB codes, go look at those". More here.

    So that makes it sound like your other codes were all on the ECB light, which would mean the 43 and 44 were C1377 and C1378, about the capacitor box.

    ABS, VSC, and ECB are all implemented inside the same ECU under the dash, but in some ways they act like different personalities and gossip about each other like that.
     
  5. punatic

    punatic New Member

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    OK some new observations. First I went to drive this morning, and the car would not go into ready mode. So I figured what the heck, I'd use that opportunity to go in and pull the plug on the capacitor box, which I did, as well as loosening and re-tightening the mounting bolts to make better connections to ground if that matters.. Lo and behold the car went into ready and I drove it, however the ((!)) light still was on. After doing other stuff I jumpered the OBDI and read code 43, cleared it and cycled the car several times and the light came back. So now I pulled all the plugs in the back, capacitor box and the two battery plugs, sprayed all with contact cleaner, and plugged and unplugged a few times to clean stuff up. Checked for codes and have none. Buttoned everything up and started on an evening drive along the ocean. Back to the first problem, car would not go into ready from P. Went in the back and plugged and unplugged again, and got it to work. Went for a nice ride, stopping a few times to shut down and restart, didn't have a ((!)) light at all. I'm guessing most of my issues here are connection related. I might have forgotten something, but bottomline is everything works as of this evening and there are no trouble lights. Still a bit concerned about the car not shifting out of P though.
     
  6. mr_guy_mann

    mr_guy_mann Senior Member

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    I might suggest searching the forums for how to obtain a copy of Techstream (Toyota's diagnostic software) and a miniVCI cable that you can install on an old windows laptop. When you own a car as complex as a Prius, it is really useful to be able to scan all possible ecu's for codes and data, and to perform certain tests and procedures just like the dealer techs can.

    If the car will go into ready mode, then I assume that the brake light switch works consistently. (you have to have a foot on the brake before it will go "ready" AND before you can shift out of park.)

    Posted via the PriusChat mobile app.
     
  7. punatic

    punatic New Member

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    Yeah I'm getting the idea...I looked into Techstream a few hours ago. I need a used Windows computer so I guess I'll belly up to the bar and buy a laptop. Any clues on getting Techstream?
     
  8. punatic

    punatic New Member

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    I just wanted to add here. I doubt any scan tool would have showed me that there were connections that had corrosion and made intermittent or no connections. In this case it would most likely show a failed component, and ironically if I changed the component and reconnected things up may have actually fixed the problem. Since I have yet to obtain these I don't know, someone out there could probably confirm or not.
     
  9. ChapmanF

    ChapmanF Senior Member

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    In your case, you got the codes you needed using the blink method, and from what the repair manual says about those codes, you knew enough to go look at the capacitor box for any reason its communication with the skid ECU could be flaky, and that was enough to solve the problem.

    The only additional benefits you might have seen from having Techstream for this issue would have been:

    • it would have given you the full codes right away, C1241, C1377, C1378, saving the step of looking up the blink codes and making sure which light blinked the 43 and 44
    • it would have given you the INF code for the C1241, which might have been further sharpened your focus on the capacitor box if it had been 83
    • it could have shown you some of the voltages in question captured in the freeze frame at the time the code was set which might have given extra clues

    In this case, you already got the same codes a scan tool would have given you, only without the scan tool, and you managed to interpret them sensibly, and avoided the mistake of thinking they could only mean a failed component. Who's to say you wouldn't be able to interpret them just as sensibly and avoid the same mistake if you saw the codes on the screen of a scan tool?

    Naturally, any trouble code an ECU in a car can give you isn't able to tell you anything beyond what the ECU itself can know. If the ECU is bolted down in a box under the dash with 20 feet of wires between it and the capacitor box, and it gives you codes about flaky signals from the capacitor box, you as the human know that it's your job to work through the possible reasons the ECU could have seen what it saw. You know the ECU isn't telling you specifically which component failed, because you know it had no way to tease apart those possibilities from its bolted-down location under the dash.

    It's true enough that people sometimes are misled by the 'fortune cookie' for a trouble code, which is usually a terse one-liner that has the name of a part in it. For example, C1378's is "capacitor communication malfunction". If somebody blindly reads the fortune cookie and thinks "oh, I should go buy a capacitor box", that might be an expensive way of solving the problem (or even of not solving the problem, if it was something else and didn't get accidentally fixed while replacing the part). But that's not the scan tool's fault. Regular PriusChat readers have already read plenty of times that they shouldn't treat fortune cookies as oracles, but should find in the repair manual what the code actually means, and then do the workup to find out why they have it.

    Maybe the blink code makes life simpler in a sense, because it doesn't show up with a fortune cookie, and you pretty much have to look in the manual anyway to find out what it means.* But if you know enough to do that with a blink code, you surely would know enough to do the same with a code shown on a scan tool, and not be misled just because the tool might also show you a fortune cookie for it.

    * ... but then I guess probably 95% of people getting a blink code aren't going to look in the repair manual either, they're going to punch it into google and see what fortune cookies come up from that, which could even be for completely different cars.
     
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