My daughter's 2005 Prius recently developed an ABS issue. If anyone can provide any insight, I would be grateful. Details below. Car: 2005 Prius Miles: 77k Problem: Recently the above lights showed on the dashboard. There has been NO recent brake work, no recent accidents, no known reasons that I know of would have introduced air into the system. Dashboard lights(Note - VSC and "Slip Indicator Lights" are NOT lit.): 1 - BRAKE 2 - Brake System Warning light (Circle with parenthesis and exclamation point) 3 - ABS Note: If I clear the ABS code, it comes back only "when" I press the brake pedal the first time after clearing the code, but to be clear, not until I press the brake pedal. Codes (as read by "Kingbollen Ediag Elite"): C1344 Hydraulic System(RL) Indications: 1 - The brake reservoir is slightly over full. With the reservoir slight overfull, I wondered if some issue is pulling air into the system. 2 - With the reservoir slightly over full, it suggests there is no brake fluid leak… unless the system is sucking more air in than is leaking… but I have seen no leak indications. 3 - The reservoir level has come down slightly when I unsuccessfully tried to bleed the brakes, now it is maybe only 1/4" above full. 4 - When bleeding the rear brakes, a small amount would drain out the rear brakes, but I could not get the pump to actuate. I was using a "Kingbollen Ediag Elite" OBD2 Bluetooth scanner, which has ABS bleed capability, but maybe I was not using it correctly, or maybe this issue prevents the pump from operating. Other things checked: 1 - both rear wheels removed, and brakes inspected, no visible leaks, brake pads appear normal (suggesting no pads are dragging), everything looks perfectly fine. Diagnosis with "Kingbollen Ediag Elite" OBD2 Bluetooth scanner: --Wheel cylinder voltage diagrams 1 - Diagram 1 - At rest, brake pedal NOT pressed, both left and right rear wheel cylinder voltages look like this at 0.43 volts: 2 - Diagram 2 - With brake pedal pressed, the other 3 wheel cylinder voltages respond. Take note that both front brakes show about 2.8 volts. The RR(Right Rear) cylinder voltage rises to 1.3 volts, BUT… the RL (Rear Left) brake cylinder volts stays low at 0.43 volts. See orange arrow. 2 - Diagram 2 - With brake pedal pressed, the other 3 wheel cylinder voltages respond. Take note that both front brakes show about 2.8 volts. The RR(Right Rear) cylinder voltage rises to 1.3 volts, BUT… the RL (Rear Left) brake cylinder volts stays low at 0.43 volts. See orange arrow. 3 - Diagram 3 - Shows RR wheel cylinder voltage shows good fluctuations with brake pedal pressure when brakes are pumped several times: 4 - Diagram 4 - Shows RL wheel cylinder voltage DOES NOT fluctuate when brakes pressed, but merely shows a small "blip" in voltage, and stays low at 0.43 volts: I had posted earlier on another post named "Help Diagnosing Persistent BRAKE, ABS, VCS, and ((!)) Lights", and Tombukt2 had said " This is all actuator control and that lil pump looking thing on pass side firewall . I believe is rear brake pump or control.". I think Tombukt2 may be referring to the "Stroke Simulator". Thank you Tombukt2, I was not even much aware of that until you mentioned it. And Brian1954 said I should create a new thread, so that is why I have created this new, and more detailed, thread. Thank you Brian1954. Meanwhile I am trying to learn more about the system so I can narrow things down, and prove which component failed, before I start replacing things. Thank you all for your help, and patience reading this long post. Mdixon1
Generally at the end of the day you're you're generally doing actuator for a few months I was doing 4 a week . I never looked to see what that thing was on the firewall mine was making a racket at one point . Actuator replacement fixed all that
it might be helpful to get a prius aware code reader and get the actual trouble codes to begin the diagnosis
I had a car here that the rear brakes had been done. I believe this was the code after much looking and fussing around what I found was the brake shoe trailing on rt side was not in the slot on wheel cylinder . This caused the tab on shoe to dig into rubber boot of cylinder push in incorrectly and cause fluid loss round the boot saw it run inside of backing plate looked at cylinder saw issue immediately put tab in slot Wella..
The OP included the trouble code in post #1. "Codes (as read by "Kingbollen Ediag Elite"): C1344 Hydraulic System(RL)" Why would the OP need a different scanner? The screenshots in post #1 look like they are from the "Kingbollen Ediag Elite" that the OP used. It looks like a very capable scanner for the brake problem in his daughter's Prius.
Funny, both bisco and I missed it, tucked into the middle of that post there. I saw all the later data stream screenshots, and thought it seemed odd to post all that and not the code(s).
I am very sorry for the delay in responding. I am very grateful for your commentary, help and interest in this problem. Contributing to my delay is this… I was carefully writing all my responses in Microsoft word, responding to every comment, and just had not posted yet… and then when I looked tonight… the document is now gone. I have no idea what happened to it. So, starting again, more abbreviated this time. Tombukt2 said: "at the end of the day you're you're generally doing actuator" Agreed. I am still researching, studying the ABS system, just in case there is something than can be done, but yes, I am 99% resolved to changing it out. Bisco said: "this thread is interesting, especially post 13. brake-code-c1344-and-warning-lights.160013" Thank you, I intend to carefully read that thread. Tombukt2 said: "… I found was the brake shoe trailing on rt side was not in the slot on wheel cylinder…" I have inspected both sides, and didn’t see any leakage… both sides are very dry, and no recent brake work has been done. Brian1954, ChapmanF, bisco: <various commentary on the scanner> Thank you all for your guidance. Bisco said: "aren't there possible sub codes?" Yes, apparently there are advanced ABS codes. I scraped the internet and found a document with the following on the bottom of each page "2004 Prius – Preliminary Release (RM1075U)". I only have about 8 pages of that doc, but apparently it is called "Toyota Prius 2004 Service Repair Manual + Wiring Diagrams". On page 05–1079 of that document, I see this indicating there are indeed advanced codes: However, based on my indications, with the Rear Left brake "cylinder volts" not responding like the Rear Right cylinder volts, I think those advanced codes aren't going to tell me much. With those 5 advanced codes, they all look like it implies rebuilding (I am assuming rebuild kits are not available), or replacing the whole assembly... just like Tombukt2 initially suggested. Even if there are other advanced codes, my reader doesn’t show any of the advanced codes. I suppose that the is the advantage of paying hundreds/thousands for the professional level scanners. Meanwhile today, I did some more analysis with my scanner, and discovered another clue… when brake pedal pressure is applied the "Left rear solenoid current" stays low at 0.0 volts instead of responding like the right rear solenoid current. However, I don’t think this additional clue tells me much, as it still suggests a problem in the ABS control module on the ABS assembly… again supporting what Tombukt2 said regarding replacing the assembly. I have been hoping to discover a bad electrical connection, or some other issue, but that seems increasingly unlikely. At this point I am just trying to turn over every stone looking for clues before replacing the module. I suspect there is a failed electronic component inside the ABS control module, but without a circuit diagram of the control board, and more info to support it, I am still looking at replacement of the ABS assembly.
In gen 2, those are two different things: the brake ECU is inside the cabin under the dash, and the brake actuator is out on the firewall. So that "Left rear solenoid current" does need to pass through a wired connection between them. But pay close attention to the circumstances. After the ECU has reported a RL hydraulic pressure issue, it is likely to lock out power to that solenoid on purpose (to avoid, say, pumping all the brake fluid out in case a leak in that line was the problem), and so the reading staying at 0.0 would be as expected. It might be most interesting to see what happens there on the first pedal press after clearing—the one that causes the code to be logged again. It might happen quickly enough for datalogging to be the only way to see it. (Even datalogging by a scan tool depends on repeated polling over the multiplex network, so if anything happens so quickly it fits in one polling interval, even scan tool datalogging might not show it, and actual instruments inserted into the solenoid and pressure-sensor circuits might work better.)
Wow, that is extremely helpful information. It gives me more info to analyze with, thank you so much. My intent is to study the Toyota/Prius shop manual and gather whatever information I can on the theory of operation so I can narrow the issue down... and there is a big fear of doing a painful replacement and finding out it did not fix the problem. As always understanding the clues and their implications is important. Thank you ChapmanF.
Problem resolved I apologize for taking so long to respond. --TLDR I had the following ABS code: C1433 Bleeding the rear left brake multiple times resolved the problem. But I theorize the problem may come back, because I still don't know how air got into the system to begin with since no work had been done, I suspect there is an old/dried rubber seal somewhere that leaked air in. But the two things you should do/check before spending/wasting your time and effort (like I did)... 1 - Make sure the automatic adjusting brake shoes are properly adjusted. 2 - Bleed the air from the affected rear brake (repeatedly?), for me that was the left rear. The following is long and rambling, hopefully it will provide additional info for those who are desperate to find a solution without/before jumping into ABS Actuator or Stroke Simulator replacement. --Details Somewhere in the official shop manual, I had seen a troubleshooting flowchart that led me to bleeding the rear brake. I can't find "that particular flow chart" now, and I don’t even know if I read it correctly. But I think it had indicated to look for leaks, and/or drum brake actuators assembly, etc. And since visually no problem was visible, the procedure indicated to bleed the brakes… so I did. It wasn’t just a single effort of commanding the ABS to bleed one time (which only lasts for 5-10 seconds). I probably commanded the bleed 20 times or more over all. Total volume bled was probably about 2 cups. I was not able to bleed the brakes without a "bidirectional" code reader like some people on internet/Youtube have demonstrated ( I am assuming it was operator error on my part). But acquiring a bidirectional code reader makes it very easy, details are further below. --Side note on ODB2 code readers: There are two low cost Bluetooth bidirectional code readers I can recommend: 1 - XTOOL Anyscan A30M V2.0 2 - KINGBOLEN Ediag Elite Both of those products have free lifetime updates. I prefer the Anyscan A30M, it appears to be a slightly nicer/more intuitive user/software interface. It is slightly more expensive, but the Ediag Elite does have a couple of things I like better, and some people may prefer the Kingbolen. Watch YouTube videos where both are demonstrated by a variety of channels. --Additional commentary During this troubleshooting/repair process I wanted to leave no stone unturned before doing the painful work of replacing either the SKID CONTROL ECU under the dash, or the BRAKE ACTUATOR ASSEMBLY on the engine side of the firewall under the inverter… both would have been very painful and time consuming. ChapmanF gave me a major clue on the Prius ABS "theory of operation" by pointing out that maybe what I am seeing is a "protective action" by the ABS system, where the ABS is detecting a situation and turning off that one particular brake. That seemed to fit the symptoms. So with that theory in mind I started analyzing for that possibility. One thing I noticed in the Toyota shop manual is that both the SKID ECU and the ACTUATOR both send signals to each other. So, I couldn't just conclude "This component is upstream and is telling the other 'blah, blah, blah...'". Both of these two major components seem to originate information and send it to the other based on the info I saw in the shop manual. So trying to determine which was upstream (and possibly the cause/issue did not have any conclusions) . But based on that commentary from ChapmanF I spent more time analyzing/looking for clues on the "live data", trying to find clues that would confirm if the ABS was detecting a situation and turning off pressure to the left rear brake. I was not able to confirm/prove it fully, but the symptoms fit the understanding I gained from ChapmanF, and I believe he was 100% correct in this situation... I just couldn’t prove it. So, it was Saturday again, and I determined it was time to try bleeding the brakes a second time. I studied the bleed procedures in Toyota Shop Manual to make sure I understood/followed any needed details that maybe I had missed before. The Xtool Anyscan A30m appears to know the exact procedure spelled out in the Prius Shop Manual. I bled the left rear brake about 4 times on Saturday, and the symptoms actually improved slightly. Before bleeding, as soon as I touched the pedal the code/ABS dashboard lights would come back on. But after bleeding the rear left brake 4 times, it took some effort to get the code to set… I could pump the brakes, turn the car off and the code would only set occasionally. I took it for a brief test drive and the code set about 4 times in a 5 mile trip… bad but still better than it was before when it would immediately set by just touching the brake pedal. So, Sunday afternoon I bled the left rear brake about 10-15 times and it NOW seems to have resolved the problem, I was not able to make the car set the code. Also when I look at the live data the left rear is as responsive as the right rear. --Hint to make bleeding the rear brakes faster/easier. If you follow the proper procedure outlined by the Xtool Anyscan A30m (and shop manual) you go through a small series of screens, selecting buttons, etc. But I just happened to discover that if you "clear codes" in that part of the software interface, after it has cleared the codes, the actuator pump runs for about 5-10 seconds. I don’t know if this is an Xtool functionality, or if it is a normal part of the ABS functionality to pump up the pressure after the codes are cleared. But the point is it takes less effort, fewer screens/keystrokes to just clear the ABS codes repeatedly (even if there are no codes) to get another 5-10 seconds of bleeding. This way you effectively stay on one screen, press the "clear codes" button, and then acknowledge the popup message, and then you can easily repeat this in a short period of time without having to traverse a series of screens/buttons. I ended up bleeding about 2 cups total between the two days. -- So what was the problem with this Prius Even though no work has been done on the system, at least in the past year (I bought it used about a year ago), and no leaks were found, somehow air had gotten in, apparently in the left rear side of the system. So, based on the commentary from ChapmanF, this is what I theorize the ABS computer was doing: The left rear brake hydraulic system was detected by the ABS ECU to not be responsive like the right rear (or at least not as much as the ECU expected), meaning fluid pressure is applied to the left rear, but detected pressure doesn’t rise as much as the ECU expected. Us humans would call that "spongy brakes" and determine "I bet I need to bleed the brakes to get the air out". But in this case I believe the ECU determines "there may be a leak in the left rear brake line" and so as a protective action the ECU STOPS sending hydraulic pressure to the affected brake line… this would be done to prevent pumping out brake fluid out of a broken/leaky brake line and leaving other parts of the system compromised due to insufficient brake fluid. And the ECU alerts the driver by setting codes and lights on the dashboard. So bleeding the air out of the left rear, caused the pressure to build up as quickly as expected when the brake pedal pressure is applied, so the ECU stops doing the protective action and no longer sets the ABS codes. -- How does air get in the system when no work has been done on the brakes Searching the internet reveals that sometimes people get air in brake lines even though no work has been done. Some of these situations involve people taking their cars to multiple shops and the problems can't be found, etc. Some people have suggested that as the brake piston seals age they get where they will seal effectively when the hydraulic pressure is applied so nothing leaks out, but then when the brakes are released, for a tiny fraction of time, there is less pressure than atmospheric and a tiny bit of air can get sucked back into the brake cylinder. After a while enough air accumulates that the ABS system will detect that one brake line applied pressure is less responsive as fluid is pumped, the ECU program determines there may be a leak, and STOPS applying fluid pressure to that brake line, and relying on the other 3 corners of the car to stop the vehicle. I can't account for the validity of this, if there really is a small fraction of time where the pressure is less than atmospheric, but it seems plausible. -- Why this problem may come back If the theory is correct, it suggests that the brake piston seals are old/dried/worn (20 year old car even though it only has 77k miles, plus being a Prius barely uses the brakes). So possibly, since I have not changed the piston seals, the problem may not be resolved... just a theory of course, time will tell if the problem comes back. However, air can come in from the ACTUATOR ASSEMBLY, not just from the brake cylinders. Someone described a situation where they unfortunately went through a series of bad actuators. He learned he could just bleed the system often, and was able to keep using the car. He didn’t say his leak was from the brake cylinders, but rather described his bad component as the "ABS module". If you are interested in that possibility, this guy tells his story: -- Manual adjustment of the drum brake automatic adjustment mechanism When I first started this investigation, I had visually inspected the rear brakes to make sure there were no leaks. Trying to get the drum off, I found it unusually hard, the shoes were gripping the drums "very" hard. So, I loosened the star/ratcheting automatic mechanism. I wasn't careful, I figured "I don't need to be careful because the automatic mechanism will readjust as needed". That was a mistake. Having the automatic mechanism adjusted too loose gave the ECU yet another reason to think the brakes were spongy and again would set the code/dashboard lights. So, don't do like I did.... adjust your automatic adjustment mechanism to be correct, do not wait and let it "take up the slack"... the ECU will punish you for being lazy. If you don't know how there are YouTube videos to help, proper adjustment videos do not have to be about the Prius, this is a thing that we have been doing for many years, long before ABS systems became popular. -- Current situation The problem seems to be resolved, but I will be driving it and of course very watchful/aware the problem could return. If it returns and I see a repeating pattern with reset codes/bleed cycles, I will then need to do more to determine the source of air intrusion. Since that might be hard to do, the simplest next step might be to replace the rear left brake piston seals and then wait and see if that problem never comes back. Or again check/clean/lube the drum brake star/ratcheting automatic adjustment mechanism. I intend to update this thread if the issue comes back. -- I am thankful to all Thank you all for your commentary, help, guidance and information. Hopefully all these painful details/commentary that I have provided will help someone else who has similar issues. ChapmanF Bisco Tombukt2 Brian1954 gdowdy3 (described a similar situation) mr_guy_mann (commented to gdowdy3, but the info helped me) SFO (commented to gdowdy3, but the info helped me) mdixon1
Very good analysis. Another way that 'air' can get into the fluid without the system having been opened is if there is a slow leak past the bellows in the pressure accumulator (the beer-can-shaped part of the actuator assembly). There's a bellows in there that has pure compressed nitrogen on one side and brake fluid is pumped into the other side, to serve as a source of high-pressure fluid. So if there's a slow bellows leak, there can eventually be what a human would call spongy brakes, except that the bubbles are straight nitrogen instead of ordinary air. Nothing makes me sure that such leaked nitrogen would find its way preferentially to the left rear brake line, but maybe that could be part of the picture. The way the Prius brake system works has the side effect of pretty much masking the feel of 'spongy brakes' from the human. Your pedal feels the same and the ECU just holds the valves open longer if it has to shoot more fluid into the 'spongy' line. So you don't really notice anything until the line is so spongy that the ECU gives up on it and makes codes.
Very interesting, I didn't know about the nitrogen. And I agree, it seems unlikely that only one side of the rear brakes would be affected if the source of "air"(nitrogen) was coming from the accumulator. Although maybe internal routing inside the ABS assembly body could have routing "higher" (allowing gravity to pull fluid down and nitrogen up, with nitrogen only entering the left brake channel. I recognize this is a far reaching theory, if this was the case it would be an "often seen thing" that only the rear left brake was affected... so, yeah, I am with you... seems possible but unlikely. And it is also worth noting that if the issue is nitrogen from the accumulator leaking past the bellows, there is only so much total volume of nitrogen in the accumulator. So any temporary remedial methods would be helpful only for a limited number of times before the total nitrogen volume has decreased enough for the ABS system to detect other issues and set other codes. So, anyway, I am hoping things are going to be stable/fixed for a while, well, hopefully forever. Thank you for your interest in my problem, you have helped me a great deal.
The chief effect of reduced volume of nitrogen in the accumulator is shorter cycling of the pressure pump: it ends up taking a smaller volume of fluid to make the difference between the pump cut-in pressure and the cut-out pressure, so the pump will run somewhat more often, just like the water pump in a house with well water if the amount of air in the pressure tank is reduced. The pump normally runs only once every few or several uses of the brake (and runs even with no use of the brake, given normally very slow leakage through system valves, maybe once or twice an hour). Many drivers seem to have a really high tolerance for the pump running much more often than normal. You can find a lot of threads here like "my pump is only running every ten seconds, do you think I should replace anything yet?". The ECU itself doesn't really seem to code for frequent pump cycling until it's so bad as to have trouble reaching target pressure at all. Whether that was the best engineering choice might be debated, but that seems to be what they went with.
OK, got it, so if I observe frequent cycling that is a major clue. Currently it is not doing that. Your understanding of the ABS system is impressive, thank you for sharing your knowledge. I am curious, were you, or are you, a Prius mechanic, or how did you acquire so much knowledge of the ABS system?
You can learn a lot browsing the full technical library (not just the repair manuals) on the Toyota TIS site: Toyota Service Information and Where To Find It | PriusChat The resources there include the same course materials the "University of Toyota" dealer technician training uses. Of course, even if you can learn a lot from a bunch of good resources, it's sort of the normal human condition that you probably won't learn a lot from them unless you are also regularly engaged in solving problems that require you to. A combination of hands-on problem solving on some Prii that happen to be local, plus remote problem solving on faraway Prii via PriusChat, makes a pretty good regimen for that. I often-enough manage to solve some Prius problem for somebody else over PriusChat before I ever first encounter it hands-on myself, and then when I do it's already familiar. So PriusChat problem solving benefits my hands-on and vice versa. I've been doing both for about 17 years now and over that many years some of the stuff actually sticks! (Plus I can search PriusChat to remember stuff I've forgotten but posted about when I learned it.) Also, solving problems remotely is good practice because it puts a premium on understanding the systems in some detail, where when hands-on you can sometimes stumble to a solution with more of a vague understanding and trying a lot of stuff.
I should investigate those docs, thank you for the link. You have given a lot of your time to helping others, including me. Thank you.
