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Vehicle speed signal correction when changing tyre size

Discussion in 'Gen 2 Prius Accessories & Modifications' started by Minima Domum, Apr 11, 2020.

  1. Minima Domum

    Minima Domum Member

    Joined:
    Apr 7, 2020
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    Location:
    Adelaide, Australia
    Vehicle:
    2009 Prius
    Model:
    i-Tech
    Hey guys,

    I'm planning to put larger tyres on my Prius soon for better ground clearance and traction (yes I know it will hurt mileage - I don't care)

    In previous cars I've been able to add an electronic module behind the dash that adjusts the vehicle speed signal so the odometer and speedometer read the correct distance/speed, is this something I can do in the Prius also? And where would I find the vehicle speed wire?

    I'd like to get the mileage screen and the speedometer to read correctly with the new tyres.
     
    #1 Minima Domum, Apr 11, 2020
  2. ChapmanF

    ChapmanF Senior Member

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    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    I believe there is a pulsed VSS that is fed to the combination meter and maybe the MFD. I have a vague memory of the wire being purple, but you shouldn't trust that (I might be remembering a completely different car). The wiring diagram (more info) is a better source.

    I think the signal is generated by the brake ECU, based on the four wheel speed sensor inputs. The brake ECU can also be queried for the vehicle speed. Naturally, fiddling with the VSS will not change what the brake ECU thinks the speed is.
     
    #2 ChapmanF, Apr 11, 2020
    Minima Domum likes this.
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