ABS, Brake and traction control alerts.

Discussion in 'Gen 3 Prius Main Forum' started by DanWF, Jan 16, 2026 at 7:52 PM.

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  1. DanWF

    DanWF Junior Member

    Joined:
    Jun 29, 2021
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    Location:
    South Dakota
    Vehicle:
    2011 Prius
    Model:
    III
    For several months I have been getting C1249, C1380 and C1391 and my ABS, Traction control and brake light come on. They will go back off for a while (maybe a few minutes, maybe a day) and then come back on.
    When this started I was driving on the highway and heard a sharp clunk under the car. I assumed I had hit something but I did not see anything in the rearview. Then I noticed all these lights on. I stopped and shut the car off and restarted, but they remained. As I drove they went off.
    When the lights are active the brakes do behave more sluggish, but hardly noticeable.
    I am thinking this is a damaged speed sensor, but I don't know how to test them and I don't have a good way to get under the car.
    Any suggestions would be appreciated.
     
    #1 DanWF, Jan 16, 2026 at 7:52 PM
  2. ChapmanF

    ChapmanF Senior Member

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    Vehicle:
    2010 Prius
    Model:
    IV
    C1249 and C1380 are probably related: C1249 is ECB reporting a problem with the stop light switch circuit, and C1380 is VSC reporting a problem with the stop light control relay.

    I would guess there is probably one underlying issue causing both of those codes, and a pretty good idea where to look might come from just comparing the 8 pages of troubleshooting steps for C1249 and the 7 pages for C1380.

    Toyota Service Information and Where To Find It | PriusChat

    C1391 is a different problem and, regrettably, not very rare as these cars age. It means the system is having trouble building and holding fluid pressure to operate the brakes, and is usually fixed by replacing one of these two units:

    [​IMG]

    The problem can be caused by either unit. The top one is the better bet if you only want to replace one and see if that did the trick; it's the one with more little valves in it and more chances to develop trouble. The cost-is-no-object repair is to replace both units.

    None of those codes would indicate a speed-sensor problem.
     
    #2 ChapmanF, Jan 17, 2026 at 4:16 PM
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