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    squallor New Member

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    2002 Prius
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    The Problem:
    The short version of the problem is that, as the description says, the ABS and Brake dash lights will come on for awhile, but then shut off, either why driving or the next time I start my car. The brake fluid level and color seems fine, and I checked the hidden service menu from the control screen, and the computer is not reporting any error codes (though I have not hooked it up to any formal error code reading device).

    Problem History:
    The first I saw this problem was about 4 weeks ago just after I got an oil change at a local Toyota Service Center. They warned me that the lights were on and I should get them looked at (though I had never had an issue with them before). when I started my car after, they were on, but then shut off after about 30 seconds. I did not see them again for a few days, so I assumed it was just something got bumped or whatnot, and was not worried. Later I randomly started my car one morning and they were back on, this time they stayed on for a few minutes before shutting off. It continued to do this randomly, but I never felt any issue with brakes, nor noticed any other problems with the operation.

    The first time I saw it come on why driving, was when I was pulling over to the side of the road, and hit a puddle that was deeper than I thought and jerked the shocks a lot. After this the problem started to be more frequent, most noticeably if I park on a hill with the e-brake on.

    My Thoughts:
    I called my Service center, and they wanted 100 bucks for the inspection, and then most likely another couple hundred for the repair. I am not inclined to just dump my money into this without looking it up first, and what I have seen online is that similar cases on other cars have been a faulty abs sensor or some kind of particle in the fluid line. Since I am not seeing any error messages from the computer, nor are the lights consistently on, I am thinking of getting my brakes flushed.

    Does this sound like the right idea? Is there anything I should know about flushing the brake fluid, or should I really take it to a service center. They are asking 130 (plus mostly likely an extra 20 bucks b/c this place always finds little things to tack on) to change the fluid. I figured I could do it myself for under 50, but wanted to check in here to see if anyone had any other advice. I am not what anyone would consider a car guy, and this is my first hybrid, so I wanted to check with some experts first.

    Thanks in advance,
    Mike
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    Patrick Wong DIY Enthusiast

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    Hi Mike,

    Especially since you do not consider yourself a "car guy" I would strongly suggest that you not attempt to flush the brake fluid. If you introduce air into the system upstream from the brake wheel cylinders, it will be very difficult to get rid of that and you will end up without brakes and having to tow your car to your local Toyota dealer.

    The "hidden service menu" that you can find on the MFD has nothing to do with powertrain or skid control system status, so please don't waste your time looking at that.

    Since the BRAKE and ABS warning lights are warning you that an important safety system is impaired, you really need to have that checked out by a competent servicer who is familiar with Prius. Normally that would be your local Toyota dealer. Good luck.
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    squallor New Member

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    Thanks for your reply.

    I wasn't actually planning on flushing my brakes entirely myself, I know someone who always does his own work on his cars, so I would actually go do it with him on the weekend (he's never had a hybrid so didn't want to say anything for sure, nor has he looked at my car himself yet). I do appreciate the concern and understand the risks with changing your brake flood.

    I am just looking to see someone had idea for other things to look for before potentially dropping a couple hundred dollars on something I could have done myself. With the service menu, I figured there wasn't going to be much there since it is never showed a warning on the digital display, but figured I would check anyway since it was a 2 minute thing for me. I heard that autozone does free OBD scans, so I was going to try and do that tonight to see if I can at least know as much as possible before hand if I do have to take it to do the dealer. I know I said I wasn't a car guy, but I have done small work on my car before, but I always like to consult with people first. I just want to see if it is anything like that before I commit a lot of money to it.

    Thanks again.

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    seilerts Battery Curmudgeon

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    ChapmanF Senior Member

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    The diagnostic screens on the MFD are cool, but they are only for diagnosing the MFD itself and other items on the AVC-LAN (radio, CD, navigation if you have it). It is separate from the information you need to get via the OBD-II DLC connector under the dash at the left.

    If you don't have a scanner, you can still read brake system codes by jumpering the TC signal (pin 13) to chassis ground (CG, pin 4) at the DLC connector (key on, engine off). Various lights on the dash will start blinking codes from the computers that control them. Also the MFD will switch into its diagnostic screen that you've already seen, except in Japanese. Count the blinks of the ABS light; you'll get two digit codes, e.g. blink blink ... blink blink blink would be 23. You may get more than one two-digit code, with longer pauses between the codes.

    It goes without saying, be careful to get the pin numbers right, don't go shorting random DLC pins together by mistake.

    -Chap
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    squallor New Member

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    I just had my OBD-II scan done at Autozone which they did for free. It did not report any error codes. I don't know if that can rule out certain problems or not.

    I will try and jumper the pin 13 and pin 4 terminals to see what if I get anything. I will report back here with what I find.


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    squallor New Member

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    Just got the abs codes: 31, 32, 34, 59.

    I tried googling for a list of abs blink codes, but I could not find any. Does anyone here have a translation?

    Thanks again.
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    ChapmanF Senior Member

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    I believe the ABS DTCs as you would see them on a scantool are all C12nn codes, and the two digits you get with the blink method are the nn.

    If I remember right, C1259 is a pretty generic code that you get if there's ever been any condition that interfered with proper coordination of the braking between the ABS and HV ECUs. Because that could be a lot of things and can likely be cleared after the underlying problem's been fixed, it makes sense to look up the other codes first.

    If it were me I wouldn't want to waste much time looking anywhere but in the service manual. A very cheap fee gives you one or two days of access at techinfo.toyota.com, if you're not planning to have the car long enough to be worth just buying a copy (the back of your owner's manual has ordering info). You don't just want translations of the codes, you want the procedures on what you need to rule out in what order before you know what's causing those codes to come up, and all that's in the manual. Not that you haven't also got google, and this forum, or 3rd-party publisher service manuals, but if you've ever played that telephone where you try to pass information along from person to person, you'll understand why it's good to get your own eyes on the original manual. And no, I don't work for Toyota. :)

    For general background, autoshop101.com has a technical article under hybrid diagnosis for the brake system. It doesn't list all your codes or much in the way of troubleshooting procedures, but it's a nice overview of how the systems work.

    -Chap
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    squallor New Member

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    After some serious google-fuing last night, I found a lookup for the abs blink codes. I found 31-34, which reports a signal error coming from the speed sensors for each of the respective tires. 31, 32, and 34 correspond to front left, front right, and rear right respectively. I could not find an error for 59 in that document though. Also to note, the ABS blink codes were not directly correlated to the C12xx codes, though I believe they did have some other related C12xx code.

    It suggested that I check that the sensors aren't shorted or open with a multimeter. Next would be follow the cabling to make sure its all plugged into the ecu correctly. Finally would be check to see if the ECU is not broken.

    Where I am stuck now is 1) finding where these sensors are in the car, and how to unplug them to check their impedance. 2) how to get to the brake ecu and check if everything is plugged in (i also what to check the impedance at the input terminal to see if it varies from the sensor itself.)

    As for the greater question of checking the ECU functionality, I have no idea how to do this. I would imagine that if that was broken itself, we would see more errors. Also, I would be curious to see what happens if I reset the ECU to factory settings in case some logic in there became corrupted.

    Since I am seeing intermittent issues with the brake/abs light, i am thinking that either something is grounding and it shouldn't, or something that is supposed to be grounded and isn't. From my understanding of electronics, this could cause the signal error on multiple sensors simultaneously.

    Also, I never had this issue until after I got an oil change, so my thought was that something might of got hit when they were replacing the filter, which might of messed with the wiring.

    Does any of this sound reasonable? Does anyone have advice on how to get at the speed sensors and ECU?

    And thanks again, you guys have been great for helping me step through this myself, and I don't think I would have made it this far without you.
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    ChapmanF Senior Member

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    You're asking all the right questions. Did I mention $15 gets you access to all the right answers at techinfo.toyota.com?

    I'm not trying to be mysterious or difficult, it's just that you've reached the point now where you mostly know what you need to find out, and it's clear what the best source is to find it out. There's not much I could add beyond hauling out my own manual and retyping stuff straight off the page (and somehow copying the pictures?). On the other hand, questions like "I found such-and-such in the manual, can you help me make sense of it" are where forum members can really feel useful helping you out.

    Did that make sense?

    -Chap
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    seilerts Battery Curmudgeon

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    I suspect a bad ground somewhere. Speed sensors will die in isolation, rather than en masse. At least usually, but I suppose anything is possible.

    However, it wouldn't hurt for you to put your car up on jackstands and remove the wheels (loosen by half a turn each lug nut before lifting). On the front, the sensor (Hall effect) picks up the movement from the tone ring on the axle half-shafts. I suggest you remove them (probably a 10mm bolt) and inspect the magnet tip for iron filings. If it looks clear, and resistance is between 1 and 2 kOhm, then 99.9% likelihood that your problem is not the sensors themselves but rather it is a wiring problem. The sensors are wired directly to the brake ECU but it may be that one of those grounds is loose. You'll need to download the wiring diagram from somewhere to figure it out in that case.
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    squallor New Member

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    That is my plan Saturday morning. I'll be going to my friend's house and we're going to take a look at all the sensors, make sure their resistance is good, clean them out, and see if that reports the same errors. If not, hopefully we can trace all the wires and find out if some shielding got scrapped through and is connecting to ground.

    Does anyone think that it could be an ECU error? I would think that if there is a problem there, then I would see a whole load of other problems, and most likely that all the sensors are broken. What other things would the brake ECU control?

    Also, for my general knowledge, I know I have been told the prius has 5 separate computers. Does this count as one of them, or is the brake ECU actually contained in the general ECU? I know at least one of the others is the dash/navigation system.
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    axleung New Member

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    Hi,

    I may be having the same problem as yours. Did you figure out what caused it? Thanks in advance.

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