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questions re: TPMS

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by jack black, Sep 24, 2019.

  1. jack black

    jack black Active Member

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    intro:
    i got new tires and a few days later the TPMS light started blinking and went on solid, that i understood was either damaged TPMS sensors or dead sensor batteries. but, i used my techstream cable, and i was surprised to see correct pressures and temps for all 4 tires. i cleared the error code C2121 and the light went away and everything is well. i did some searches and on some other toyota forum it was suggested the sensors need to initialized after tire change. BTW, the teachtream reported sensor voltage as "less" for one sensor (ID3) and "over" for the other 4 sensors (including the non-existent ID5).

    questions:
    1. why C2121 was triggered if there is no problem with ID1?
    2. is there indeed an initialization procedure for the sensors?
    3. what "less"/"over" means for sensor voltage?

    thanks!
     
    #1 jack black, Sep 24, 2019
    Last edited: Sep 24, 2019
  2. ASRDogman

    ASRDogman Senior Member

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    Hidden underneath the steering wheel is a button you push after you get new tires, or change your tire pressure.
    Without pressing the brake pedal press the start button twice. When every finishes, press and hold that button,
    you'll see the warning light start to blink. When it goes out release the button.
    Press the start button to turn the car off.
     
    #2 ASRDogman, Sep 24, 2019
    Rebound likes this.
  3. fuzzy1

    fuzzy1 Senior Member

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    The TPMS system only needs to be reprogrammed after a sensor change, to recognize the new sensor serial numbers. If you still have the same sensors, undamaged, you should be good to go.

    That said, I have been experiencing very infrequent read failures that trigger spurious temporary alerts. These go away with time. See my description:
    TPMS light, once, but pressures fine? | PriusChat

    The initialization procedure mentioned above should be for adjusting pressure thresholds. For when you decide to change pressure strategy, and also a good idea after sensor changes.
     
    #3 fuzzy1, Sep 24, 2019
    Last edited: Sep 25, 2019
    Mendel Leisk and jack black like this.
  4. RobH

    RobH Senior Member

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    Colder weather brings lower tire pressures. If a tire pressure is close to the trigger point, you may see the warning light. Once the car is driven a ways, the tire pressure increases, maybe even enough to clear the warning. In any case, the pressure is on the low side and needs to be topped off.

    Techstream shows you the current and trigger pressures. Using the button on the dash sets the trigger point, based on some percentage of the current pressure.
     
    #4 RobH, Sep 25, 2019
  5. jack black

    jack black Active Member

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    thanks fuzzy1, it's helpful info.
    as for that voltage info, i found it on another forum:
    "Techstream doesn't actually show the battery voltage, just an Over/Normal/Under indicator"

    weird, because mine reads low and over.
     

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    #5 jack black, Sep 30, 2019
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