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Replaced 12v battery, now brake fuse keeps blowing

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Launce, Mar 5, 2023.

  1. Launce

    Launce Junior Member

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    I replaced the 12v auxiliary battery on my 2004 Prius, but when I started the car, the yellow exclamation point warning ((!)) keeps coming on after a few seconds. Brakes seem normal.

    Tried the OBD jump reset, no joy.

    I checked the fuses and found that Fuse 40 (see picture) was blown. The manual labels it "ABS MAIN3 15A: Anti−lock brake system".

    When I tried to replace it, with the car off, there was a spark and the new fuse had blown.

    I suppose a new brake fault could have occurred simultaneous with the battery replacement. But that seems a very unlikely coincidence.

    To replace the battery, you unbolt the brake controller box and move it out of the way, taking care not to disturb its connections. But maybe it did cause a short in the controller hookup?

    Any ideas?


    Inkedpic-8263613171322057027-1600x1200.jpg
     
  2. ChapmanF

    ChapmanF Senior Member

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    If I was right about the fuses in this post, then ABS MAIN3 is the one that supplies the capacitor backup, so yeah, I'd be double-checking the connections back there,
     
  3. pasadena_commut

    pasadena_commut Senior Member

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    There is a black box right next to the battery which has electrical wiring and says something about the brakes. Perhaps when the battery was changed the cable to this box was not securely reseated? Or maybe it isn't seated at all and that plug is shorting out to the body?
     
  4. ChapmanF

    ChapmanF Senior Member

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    Indeed, that's the thing mentioned in post #1 and post #2.
     
  5. Launce

    Launce Junior Member

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    Yeah, something shorted out in the brake power supply control module. Now I have all the brake lights on and no power assist.

    Guess I'll shop for a used module.

    Thanks.
     
  6. JiPe_az

    JiPe_az Junior Member

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    Any update on this?

    I am experiencing the exact same problem on my 2004. As soon as I try to replace that 15A fuse it blows and I have the yellow brake light warning on the dash.
     
  7. JiPe_az

    JiPe_az Junior Member

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    UPDATE: Yellow (!) brake symbol is now cleared.

    SYMPTOMS:
    The car was braking fine, and the power brakes worked but the yellow (!) symbol was illuminated.

    PROCEDURE:
    The first thing I did was check the level of brake fluid in the reservoir. Level was GOOD
    I next took off the wheels to check the status of the brake pads and looked for any loose or damaged connectors at the wheels - everything was GOOD
    I next checked ABS fuses.
    • ABS-1 (25 Amp fuse) - GOOD
    • ABS-MAIN1 (10 Amp Fuse) - GOOD
    • ABS-MAIN2 (10 Amp Fuse) - GOOD
    • ABS-MAIN3 (15 Amp Fuse) - BAD
    So I do the obvious thing and try a new 15-amp Fuse for ABS-MAIN3. It Immediately blows as I try to insert it (I can hear it "pop") - BAD

    I already had a bad wire to the fuel pump in this car so I decided to check the wires. This circuit goes from this 15 amp fuse through a connector located near the passenger side kick-panel (connector is called IN1 in the manual) and then continues to connector B18 on the Brake Control Power Supply in the back of the car right next to the battery.
    • The wire from the fuse block (outside pin) to the connector in the left kick panel is blue. I locate the wire and test the continuity. I get a nice loud beep. I then tested the continuity of this section with a chassis ground - no beep and no numbers. The last thing I do is check the resistance of the wire to ensure it is low - GOOD
    • Next, I unplugged the wiring harness from the Brake Control Power Supply and tested continuity between the blue wire at IN-1 and the B18 connector at the Brake Control Power Supply. The continuity test was GOOD. I then tested for continuity with a chassis ground and no beep, finally resistance of the wire is low - GOOD
    • I left both the connectors (IN1 and B18) both unplugged and went and installed a fresh fuse. The fuse did not pop and I verified it was OK with testing continuity across the fuse. I then tested IN-1 for 12V and was able to verify 12.6V at IN1 on the blue wire. GOOD
    • Next, I plugged IN1 back in and tested for 12V at the rear of the car at B18 - 12.6V was verified. GOOD
    • So at this point, I was fairly sure that the wire was OK the only thing left was to replace the Brake Control Power Supply.
    • I got a used Brake Control Power Supply from a local salvage yard and installed it.
    • I verified that the fuse did not blow and that the yellow (!) light did not come back on - SUCCESS!

    BONUS: So I took the Brake Control Power Supply module apart to see if I could see any obvious defects (but marks or discoloration on any of the pins). One thing that I did notice was that the bolt that was holding the module on top was WAY longer than the bolt I got from the salvage yard. I could also see that the bolt on the old module had gone through the case and hit some metal that was near the circuit board. I suspect that this might have been the reason it was blowing fuses (I have not verified)

    Anyway, I hope that helps someone else out.

    Juan
     
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  8. theory816

    theory816 Junior Member

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    Wow I like they style of write up. Very clear and easy to follow.
     
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  9. Apephamous

    Apephamous New Member

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    where is the Brake Control Power Supply located?
     
  10. Brian1954

    Brian1954 Active Member

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    In the trunk, it is close to the 12v battery.
     
    #10 Brian1954, May 12, 2024
    Last edited: May 12, 2024
  11. TMR-JWAP

    TMR-JWAP Senior Member

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    Located as mentioned in earlier post, BUT if you are experiencing this problem with the 15amp fuse popping, it's much easier to just unplug the car wire harness from the capacitor power supply module and replace the fuse. If it pops, then there's a problem in the wires. If it doesn't pop, replace the box (which is most likely)
     
  12. ChapmanF

    ChapmanF Senior Member

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    The exact problem that Juan found (someone reinstalling the brake power supply with a too-long bolt on top, that drove down into it and shorted it out) seems like one of those stories that perfectly explains Juan's issue and probably isn't going to be the exact answer for anybody else (unless they've made the exact same installation mistake).

    But the techniques for how to narrow down where the fault is, those will work for everybody.
     
  13. Jreres51

    Jreres51 Junior Member

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    I read and read and can’t find my problem or a fix for it .
    The car sat for 6 weeks without starting it and when I went to move it , the battery was dead dead . No interior lights anywhere . No dome no dash . I jumped it using the points under the front hood.
    I drove it around for a half hour or so and shut it off. All the lights went to zero again .
    I left the jumpers on for a hour with my jeep running . I took off the cables and dead again .
    Is there a reset somewhere ?
    What am I missing ?
     
  14. TMR-JWAP

    TMR-JWAP Senior Member

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    A good 12v battery?
    Any chance you connected the jumper backwards?
    Can you see the security key symbol flashing on the dash when you approach the car and look inside?
    Door ajar light when you open a door?
    Measure voltage at the underhood jump point?
    Are the 12v battery cables tight on the terminals and where the (-) cable fastens to the car body?

    The car started normally when hooking up jumper cables to the underhood jump point.
    Will it do the same if you connect the jumpers to the terminals on the 12v battery?
     
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  15. Jreres51

    Jreres51 Junior Member

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    I went to a local service station and talked to the manager .
    So, the way this started was the 12v battery was replaced , the car was driven for 3 hours
    ( stopping once) and the car was parked . The car was not touched for six weeks . When I went to start it ,I needed the key to open it and the car had no interior lights . I jumped the car and it started right up.
    Today I was told that the car puts itself to sleep and to jump it and drive it for a hour and all will be well . I did that and after driving it for a hour , and shutting it off , all went dead as before . Tomorrow I will take a voltage reading , start the car, and check the voltage again .
    If it is not at least 12v I guess it will be the dc/dc inverter . Thoughts ?
     
  16. mr_guy_mann

    mr_guy_mann Senior Member

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    It could be that there is some excessive parasitic draw that drains the 12V battery when the car is off. 6 weeks of inactivity is way too long, even with "normal" key off draw. An hour of run time isn't enough time to restore the 12V. If there is high draw ghen the battery dies again.

    A fully discharged AGM battery can take 6-12 hours to recharge with a "smart" AGM compatible charger. This assumes that the 12V wasn't damaged by going to 0V.

    Normal key off draw on a SKS Gen2 is about 15mA.

    Posted via the PriusChat mobile app.
     
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  17. TMR-JWAP

    TMR-JWAP Senior Member

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    If you need to charge the battery, DO NOT use a standard lead acid battery charger. It WILL damage an AGM. The Toyota S46B24R battery specifies to not exceed 4.2 amps or 10 hours when charging. Inexpensive 3 amp smart chargers are commonly available, even at walmart.
     
  18. Jreres51

    Jreres51 Junior Member

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    I saw this morning that there are fuses right at the positive battery post. I will check that this morning