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Tire pressure light on

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by Val Rousseau, Apr 18, 2021.

  1. Val Rousseau

    Val Rousseau New Member

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    I checked the pressure of my tires and it is correct. But the tire pressure light is on. I checked all the fuses, they're all good. So I tried to use Techstream and a J2534 cable to see what's wrong. The software can't make connection with the pressure sensors, none of them. I would understand if one of the sensors was bad, but it is hard to believe that the four of them are bad. Plus, the software in principle can indicate the sensors that are registered. But in my case, it cannot even access this information. It is like if the module that collects the information form the sensors is just missing. Does anyone know where this module is supposed to be located?
     
  2. bisco

    bisco cookie crumbler

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    sorry, no. is there a tpms switch under the steering wheel?
     
  3. Val Rousseau

    Val Rousseau New Member

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    Yes, there is a switch, I mean a push button.
     
  4. sam spade 2

    sam spade 2 Senior Member

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    I suggest that paying a dealer a "diagnostic fee" might be a very good investment in a case like this.
    YOu could spend a LOT of money on wrong guesses.
    And it is possible that your test equipment isn't working right either.
     
  5. Val Rousseau

    Val Rousseau New Member

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    I believe it works right. With it I was able to successfully register a new key fob. It gives information about various parts of the car. It is only with the TPMS that it is unable to establish any connection. That's why a suspect there is something wrong with that module, and wondering if it is even still present in my car (I bought it when it already had the issue). It doesn't cost anything to check if that module is still present in my car or not, as long as I can figure out where to look for it.
     
  6. ChapmanF

    ChapmanF Senior Member

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    You've got Techstream and a J2534 cable, so you clearly see the value of preparing yourself well to work on the car. The other piece of good preparation that I'd encourage is to get familiar with the information available to you from Toyota, including the Repair Manual and Electrical Wiring Diagram. Elektroingenieur built a very helpful wiki page about that, here.

    Is Techstream in fact showing you that it cannot establish communication with the tire warning ECU? When you do a Health Check, you should get a result page showing every ECU in the car, with coloring to indicate whether Techstream was able to reach it.

    For the location of the ECU, see L4 in this screenshot from the Electrical Wiring Diagram:

    L4.png

    You may be able to see it by removing the lower glove box, which is easy. It will be an upward reach from there, above the lower tier of slots in the ECU hotel back there.

    If Techstream really isn't able to communicate with it, I would suggest turning directly to what the Repair Manual says about that situation and how to troubleshoot it; it's a pretty uncommon situation, so there won't likely be many PriusChat members saying "oh yeah, that happened to me, it was ...".
     
  7. AW82

    AW82 Member

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    Maybe a dumb question, but have you attempted to do the TPMS calibration procedure? Air up the tires to proper* inflation, press the power button twice without foot on the pedal, press and hold the TPMS button until the dashboard icon flashed 3x slowly, let it sit like that for 3-4 minutes, then power off.

    *Based on your definition, the owners manual's, that of hypermilers, etc.
     
  8. ChapmanF

    ChapmanF Senior Member

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    Honestly, if the OP has already connected Techstream and as reported it wasn't able to connect, that already confirms something is amiss beyond adjusting the setpoint (which is all that button is for).
     
  9. sam spade 2

    sam spade 2 Senior Member

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    So.....how is it that you were able to obtain the engineering spec's for that module so that you KNOW that is all the button is for ??
    Hint: You don't know that at all.
     
  10. bisco

    bisco cookie crumbler

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    have you tried resetting the pressures?
     
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  11. Val Rousseau

    Val Rousseau New Member

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    I did, but that was before before I got my Techstream cable, so I may try again. I will post an update.
     
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  12. Grit

    Grit Senior Member

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    could be a chance that batteries in all the sensors have ran out of charge.
     
  13. Val Rousseau

    Val Rousseau New Member

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    I don't think so. From what I read, Techstream should still be able to make a connection with the TPMS module, and this module should then report that the sensors are malfunctioning. But in my case, Techstream just can establish the connection with the module.

    When you install new pressure sensors, you have to register them with Techstream. And for this Techstream connects to the TPMS module. So I should have the connection with it, whether the sensors are working or not.
     
  14. bisco

    bisco cookie crumbler

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    how is the 12v health?

    did you have to hook tech stream up to the obd to register the fob?
     
  15. Val Rousseau

    Val Rousseau New Member

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    The 12V battery seems to be pretty good. No problem cranking the engine, even after not using the car for over a week.

    Yes, I hooked up Techstream to the OBD with a J2534 cable to register the fob. I actually even made a video tutorial of the procedure:
     
  16. bisco

    bisco cookie crumbler

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    i wonder if the tpms ecu connector might have some corrosion.
     
  17. Val Rousseau

    Val Rousseau New Member

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    That is very possible. I can see that all the panels in this car have been removed (and most of them improperly put back), and that all the wires under them look brand new. I suspect this was a "hurricane-damaged car", and that something happened to the TPMS ECU. I hope it is only corrosion in the connector.
     
  18. ChapmanF

    ChapmanF Senior Member

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    Hmm. If you think that might be the case, you may want to review this TSB and do some very careful proactive investigation of the car, as outlined there, to get as informed an idea as possible what has been replaced already and what future surprises may await.
     
  19. fuzzy1

    fuzzy1 Senior Member

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    I should note that my 2012 Prius has experienced several episodes of spurious TPMS alerts (a tire gauge shows good pressures) over the past several years. It may alert a half dozen times on a long trip, for ten minutes at a time before extinguishing for a while, then alerting again. This may happen on several different days over a few weeks, then not repeat for nine months, then re-appear again. It has not re-occurred since the initial Pandemic restrictions, possibly due to reduced overall driving providing fewer opportunities.

    When it initially suffered several episodes, it happened on both my summer and winter wheel sets (separate wheels and TPMS sensors) in the same month, straddling the seasonal tire swap. Linear Logic was then offering a free firmware update for ScanGauge-IIs, to display individual tire pressures, so I took the offer. No more TPMS alerts happened for the next six months.

    When the alert finally did reoccur, I was able to figure out that is was a single sensor not being detected and read for longer than the maximum time limit, then clearing when that sensor would suddenly reappear. When turning the car Off then back On, this sensor would appear as -14.5 psi (i.e. no reading, so stuck at the power-on default value of 0.0 absolute, minus sea level 14.5 to get 'gauge' pressure) while the others would show a reasonable value 35-42 psi. If it was triggered while driving continuously on the highway, the car gave the ScanGauge the last read value. That means the fault wasn't flagged on the ScanGauge, only as the car's TPMS light being lit up, except that the faulty location was showing an unchanging pressure, while the other three locations were showing slightly changed pressures as ambient/road temperatures changed.

    I should be tracking this over multiple tire swaps and rotations, to see if the "bad" sensor is always a specific sensor (per seasonal tire set) or a single wheel location. I'm thinking that it has been different sensor codes, but these episodes are sparse and I haven't kept the necessary data.

    Sorry to not yet have a solution, but my experience might provide some directions to further investigate.