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2005, Brake Issue C1252, C1256

Discussion in 'Gen 2 Prius Technical Discussion' started by HBS, Nov 1, 2018.

  1. HBS

    HBS Member

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    I was wondering if someone could lend me some advice on a brake problem with codes (C1252, C1256)? I am working on an '05 that had blown the 25 amp ABS-1 fuse and also the ABS-2 soldered fusable link. I replaced those and had the same problem so I replaced the abs actuator pump assy. (twice), the skid control ecu and the four abs relays and bled the brakes twice. The reason I replaced the abs relays is because the whole time there has been a recurring clicking noise coming from what seems like one or both relays. I've also tried the obd pin method to clear the codes several times. Any help or advice on what steps I can take to find the problem would be greatly appreciated! Thank you.
     
    #1 HBS, Nov 1, 2018
  2. ChapmanF

    ChapmanF Senior Member

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    Relays make clicking noises; it's what they do. Normally you might not notice much, because of the pump making a pumping noise at the same time. Is that happening? I don't think you mentioned...

    -Chap
     
    #2 ChapmanF, Nov 1, 2018
  3. HBS

    HBS Member

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    Hello, and thank you for responding. So the pump fails to make any pumping noise at all, but the relays make a distinct clicking noise, actually several clicks occu,r when I press on the brake pedal, even when the car is not running or in ready mode. And when the car is running, the abs relays click every few seconds like it is trying to start the pump and then after three seconds the abs mtr or the abs no. 1 clicks.
     
    #3 HBS, Nov 1, 2018
  4. HBS

    HBS Member

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    Here is a video of me pressing on the brake pedal while the car is off. It also clicks and drains the 12v when the car is off.
     
    #4 HBS, Nov 1, 2018
    Last edited: Nov 1, 2018
  5. ChapmanF

    ChapmanF Senior Member

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    So no pumping noise ⇒ power not reaching pump motor, or pump motor seized and drawing locked-rotor current (that would probably blow fuses, as you saw at first). Battery draining when car tries to run motor ⇒ not just an open-circuit problem, there is some power going somewhere. A severe voltage drop on the way to the motor might result in insufficient power to spin it, but still power drained from the battery. I'm assuming you haven't somehow scored three seized pump motors in a row....

    Those are some ideas to follow up on. A good way to start would be to get the repair manual and study the actual detecting conditions for the codes you've seen. That could give you some information, while you sit in a comfy chair, that you could otherwise only get by grabbing a meter and backprobes and digging down to some rather inaccessible connectors. It may come to that anyway before you're done, but no reason to work harder than necessary.

    A while back I wrote a post that was really about diagnosing ECU-monitored systems in general but just happened to use the Gen 1 brake pump monitoring circuits as the example. There may be some Gen 1 to Gen 2 differences that you'd be well advised to absorb from the manuals, but that post should give you some concrete ideas about how the ECU can help you with this kind of troubleshooting.

    -Chap
     
    #5 ChapmanF, Nov 1, 2018
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  6. Vako

    Vako New Member

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    Did you find the problem? I already replaced abs actuator
     
    #6 Vako, Nov 24, 2019
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