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Rear Brake lights stuck on all the time

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by Hlfxprius, Jun 13, 2021.

  1. ChapmanF

    ChapmanF Senior Member

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    Driving through slush would be, I would think, more of a factor for the more exposed connectors like those at the wheel sensors. The connector at the brake ECU is at least up under the cowl and fairly sheltered from the immediate road conditions ... but I guess you might have a bit of a corrosive atmosphere there in general, and it's still out in that.
     
  2. Hlfxprius

    Hlfxprius Junior Member

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    Do you think I can take the wipers and wiper assembly off and the plastic housing below it and get at the connector for the ECU, do you think it would be worth look at the connector for corrosion before removing and installing a new MasterCylinder unit?
     
  3. ChapmanF

    ChapmanF Senior Member

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    I am sure if it happened to me that's exactly what I would do, and if I didn't see a correctable problem at the connector itself, I would even investigate whether it's possible to open that side of the assembly and get the circuit board out for a good looking over. I have not seen anyone here report trying that before, or how far they got. It is also what I would do if I ever got the hazard-flashers-go-with-road-speed syndrome. If there turned out to be a way to get to the circuit board without damage, and find a correctable issue, and without having to muck with all the hydraulic disassembly of exchanging the whole unit, I would report that here as a success.

    Naturally, as that's an unofficial and uncharted procedure, I'd have to accept the risk that either (a) it doesn't come apart that way at all, or (b) it does, but that wrecks it and then a replacement is needed anyway.

    There's a good chance I would really begin by buying the cheapest non-guaranteed probably-broken salvage unit I could find, just to explore how it goes together, in the comfort of a well-lighted workbench.

    Or if anybody ever had one replaced because of the hazards-with-road-speed syndrome, see if they could be talked into sending the old one to me.
     
  4. Hlfxprius

    Hlfxprius Junior Member

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    Sounds like exactly what I want to try, I'll start by looking at the connectors if I can get to it without having to remove hydraulic lines. I'll let you know how it goes, will probably be a few days until I have the time.
     
  5. ChapmanF

    ChapmanF Senior Member

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    In your case there are still some simple checks with a multimeter I would want to make before even digging in for the ECU, or I would want a rundown of exactly what and how the dealer technician checked, detailed enough to be sure it covered what I would have checked.
     
  6. Chaman

    Chaman Junior Member

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    I am also facing the same situation you are although my brake lights are constantly on after I replaced my actuator (master cylinder) with a used one. I was getting the C1391 code because of which I got both my accumulator and actuator replaced. The code and dashboard lights went away afterwards; however the brake lights remain on.

    Were you or the dealer able to figure out what the problem was?
     
  7. Hlfxprius

    Hlfxprius Junior Member

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    They believe it's the brake ECU that's part of the master cylinder. But they wanted to do further testing to confirm, but I havn't had time to get the car back to them yet. I'll post here as soon as I figure out what resolved the problem
     
  8. Chaman

    Chaman Junior Member

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    Thanks. For me, it turned out to be a faulty brake switch. It appears we damaged it while replacing the actuator or the master cylinder. Replacing it with a new brake switch solved the issue.
     
  9. ChapmanF

    ChapmanF Senior Member

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    Good to know that you weren't facing the same situation. The one in this thread involves a C1380 code and isn't the brake pedal switch.
     
  10. preck

    preck Junior Member

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    My 2010 Prius has similar problems - everything was fine until 5 weeks ago - then came all the warning lights, etc. I ordered a new front wheel speed sensor, but that gave no change. One day later the brake lights started to stay on continuously; and also Techstream wasn't able to fix the Linear Solenoid Valve Offset (one of the original trouble codes, but now just history).
    2 days ago, there were a dozen codes in Techstream under ABS/VSC/TRAC, but today only C0200 and C1380 remain, plus P1578.
    The car only sat in the driveway, so I'm suspicious that there may be connector problems at an ECU.
    I did replace the front sensor but the bearing is noisy, so that will be replaced only if I can fix the lights.

    Since the other trouble code points to the Stop Light Control Relay, I ordered a used one from eBay and I now have the "bad" one apart for a look. It is an electronic "relay" circuit with IC's and power devices, and there is a missing bit of copper circuit connected to the ACC input pin. If I can repair the copper trace, should I then try it in the car or check other things first?
    Would it be worthwhile to burrow in to the ABS assembly to check all of the ECU connectors for corrosion?

    Thanks in advance for any suggestions you may have :)
     
  11. preck

    preck Junior Member

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    It may have been only a cold solder joint....
    paul
     
  12. Mendel Leisk

    Mendel Leisk Book Cover Judge

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    What's your approx location? Any evidence of rodents?
     
  13. ChapmanF

    ChapmanF Senior Member

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    Any programs that train rodents to solder better?
     
  14. preck

    preck Junior Member

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    St. John's, NL, Canada - no evidence of rodents, but we're near the ocean so that plus road salt during our winters leads me to suspect corrosion
     
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  15. preck

    preck Junior Member

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    I did teach a workshop course for a few terms that had a soldering component, but this circuit board has surface-mount components - beyond my experience :)
     
  16. preck

    preck Junior Member

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    I reinstalled the stop light relay and there is no change - brake lights are still on.