Has anyone decoded the canbus messages for the steering angle sensor?

Discussion in 'Gen 3 Prius Technical Discussion' started by Lou Faustini, Mar 4, 2025.

  1. Lou Faustini

    Lou Faustini New Member

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    Hi everyone,

    I have a steering angle sensor in my (new to me) Prius that is showing a rock-solid -850 degrees in Techstream, no matter how much I rotate the steering wheel. It simply won’t change.

    Being an engineer-nerd, I couldn’t resist taking the device apart, and I have to say—it’s an engineering masterpiece. From what I can tell, it works using two Hall-effect sensors, each driven by a gear attached to the steering shaft. The clever part? One magnet is mounted on a 25-tooth gear, while the other is on a 26-tooth gear, which allows the system to resolve absolute position over multiple turns. Genius!

    My suspicion is that the clock spring was replaced, and in the process, someone unknowingly spun the steering sensor by hand a few times. They likely didn’t realize that the sensor has a mechanical non-volatile memory of its absolute position. I’m guessing the previous mechanic assumed that since the sensor locks into the clock spring with a keyway, its overall position wouldn’t matter.

    Has anyone experienced this issue before? Any insights on how to recalibrate or reset it?
    I guess my over-all goal is to bench test this without it being on the car.

    FYI: Here are some pictures of the inside of the sensor.
    PS: I have tried the Zero Point Calibration in Techstream several times, but it has not fixed the issue.
     

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    #1 Lou Faustini, Mar 4, 2025
  2. Tombukt2

    Tombukt2 Senior Member

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    Yeah doesn't your generation 3 clock spring have a little window in it that you rotate the mechanism round and round until the red line lines up with a white or red dot on the plastic housing and then you snap it into position on the car of course plugging it in and so on Chapman will be a long to talk about the hall effect sensors in a minute genius yeah I guess And if you put the clock spring on right everything should come out correctly so maybe you'd check that before or you have You just didn't mention it? I'd be interested to know too I read about this or royalty auto had a problem like this on another vehicle and I can't remember what the end all be all was they either replace the steering angle sensor or the computer that all that information's fed into but it was very similar I replaced the clock spring on my generation too and it is just the way is described above I've only taken my steering wheel off a generation 3 to put it in my generation too because the generations are ease of all failed and we have no interest in fixing them but the steering wheels relatively nice but I didn't pull the plastics off to look at the clock spring but I'm pretty sure it may have a window so you can line it all up before you snap it into place.
     
    #2 Tombukt2, Mar 5, 2025
  3. ChapmanF

    ChapmanF Senior Member

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    Can you give more information about what zero point calibration in Techstream you tried? What menu sequence got you there?

    I ask because I don't believe there is one for the steering angle sensor. As I understand it, the skid ECU does transform the reading from the angle sensor into an absolute reading as described here.
     
    #3 ChapmanF, Mar 5, 2025
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