TPMS Management with Techstream

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by wjtracy, Mar 5, 2016.

  1. RobH

    RobH Senior Member

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    About 5 years ago I was studying the various messages that the TPMS ECU sent and received. One of the things I discovered was that the Prius ECU supports 5 sensors, just like a few other Toyota vehicles. I bought a sensor, had it installed, and set the ECU for 5 sensors. It all worked, and I've been able to read the spare tire pressure with Techstream instead of digging the tire out of the trunk. Everybody else was complaining about even having TPMS, so it didn't seem worth mentioning that you could add another sensor.

    The program I used was a one-off test, and doesn't even exist anymore. But if someone wants to write a program to enable TPMS on the spare, here's the GEN2 protocol from my records:

    82 2A F0 21 06 ......... Query # sensors registered
    84 F0 2A 61 06 x0 y0 ... Reply: x=main set, y=2nd set
    ........................ x:8= 4 sensors, x:A= 5 sensors (high 3 bits of Each byte)

    84 2a f0 3b 06 x0 y0 ....Set # sensors that can be registered.
    .........................x=main set, y=2nd set
    .........................x:8= 4 sensors, x:A= 5 sensors (high 3 bits of Each byte)
    82 f0 2a 7b 06 ..........Reply


    Specifically, the 3rd message is the one that sets the number of active sensors. "84" specifies 4 data bytes, "2a" is the address of the TPMS ECU, "f0" is the address of the interface, "3b" is the set command, "06" is the function number, and "x0 y0" are the new values. The high order 3 bits of x and y represent the number of active sensors, with the 3 bit values of 4 and 5 being the only ones tested. Perhaps values 0, 1, 2 & 3 would also work.

    You must use a Drewtech or MiniVCI interface - the ELM doesn't support the protocol used (forget about using Torque). The Drewtech website documents the API.

    Note also that the "y" field determines the number of sensors in the second set. There is probably a pin on the ECU which, if grounded, selects a second set of TPMS sensors. Comparison of TPMS ECUS between the Prius and some other Toyota vehicle that supports the second set might reveal where the signal is controlled. Several Lexus vehicles have a selector switch in the glove compartment.
     
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  2. Mendel Leisk

    Mendel Leisk Senior Member

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    5 sensors probably because full size spares might be used?
     
  3. wjtracy

    wjtracy Senior Member

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    ...hmm...worth a try if only to get advanced hacker college degree...I have not seen any other software way to fake out the TPMS

    ps- nice work!
     
  4. wjtracy

    wjtracy Senior Member

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    In the continuing TPMS saga, we had to replace flat tire due to a huge puncture, so I purchased a new OEM Denso TPMS from Amazon for the replacement tire.
    • DENSO 550-0103 on Amazon seems to fit 2006 Prius well. The reason I mention this is the Amazon fit guide now says it does not fit 2006 Prius, but I think the Amazon fit guide is wrong.
    • I paid $32 but the price changes all the time, for some reason
    • The new TPMS looked like a replica of the old TPMS removed
    >>TPMS crazy new finding:
    The old Denso TPMS removed from the flat tire was still working now at 10-years old.
    So I was fiddling with Techstream and trying to figure out how to fake a good pressure reading on this un-installed TPMS, and I noticed squeezing the TPMS in my bare hands gave me 8 psig.

    Then I tried putting the TPMS in a big binder clip, and this gave me a 50-psig reading!! This turned off my TPMS warning light!! so now my TPMS system is reading 3 real tires and 1 binder clip...which gives me 75% coverage except for the one bad TPMS unit. See if this keeps working.

    IMG_1621.JPG
     
    #24 wjtracy, Sep 8, 2016
    Last edited: Sep 8, 2016
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  5. PriusFruit

    PriusFruit Member

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    Thanks for putting forth all this information! It was helpful.
     
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  6. wjtracy

    wjtracy Senior Member

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    Thank you./ I still have 3 good TPMS at 11+ years and 165K miles, and one fake reading per above
     
  7. Sezy

    Sezy Active Member

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    I'm in the same boat with a sensor that is going out then has a good streak for a while but wanted to ask are you just doing this as an experiment instead of having the one bad sensor replaced? I have a new sensor and am looking at new tires so was going to use TechStream with your tutorial to narrow down which TPMS sensor is bad once it's light comes back on then swap it when I get new tires since they'll have access to the TPMS. Writing down the TPMS ID before of course.
     
  8. wjtracy

    wjtracy Senior Member

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    Yes I am doing an experiment but I would fix it if I had any tire work planned. By faking out the system for one bad sensor, at least I have 3 tires TPMS working. Mine are 12-years old so I would replace them any time I had the tire off. For the good of PriusChat, I wanted to see how long they could last.

    I would say after about 7-8 years you should replace TPMS anytime you are replacing tires. Unfort I did not understand that until after I put on the new rubber, and then one failed at 9 years.
     
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  9. wjtracy

    wjtracy Senior Member

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    ...the binder clip TPMS fake out method is still working 18-months later FWIW
     
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  10. Mavi

    Mavi Active Member

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    So did you install a new denso one in the spare and the old spare one into the messed up tpms sensor? A bit confused where the sensor that you put the fake out method goes.
     
  11. wjtracy

    wjtracy Senior Member

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    Front Right Tire (old OEM TPMS - went BAD)...so I am not able to monitor this tire
    (#1) Front Left Tire (old OEM - still GOOD)
    (#2) Rear Left Tire (new OEM- GOOD) - we had a flat tire so I put a new TPMS in the new tire
    (#3)Rear Right Tire (old OEM-still GOOD)
    (#4)In glove compartment (old OEM in binder clip - still GOOD) - taken out of flat tire above

    So this allows me to monitor 3 out of 4 tires, and turn the light off even though I have a bad TPMS
     
    #31 wjtracy, Mar 2, 2018
    Last edited: Mar 2, 2018
  12. Mavi

    Mavi Active Member

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    Any reason why you didn't change the trmp on the front right tire like you did in #3? Guessing you're just waiting for the tire to need to be replaced first?
     
  13. wjtracy

    wjtracy Senior Member

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    Reply yes one thing is I was trying to see how long the others would last I would never have expected 12 years (in July). Was also looking for ways to get the light out without fixing the tire.
     
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  14. Sezy

    Sezy Active Member

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    Each time I get the TPMS error and hook the car up to my computer to open Tech Stream it clears every time on it's own. This does not help in determining which is bad. Any suggestions on keeping the error up so Tech Stream can read it?
     
  15. wjtracy

    wjtracy Senior Member

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    We never really had that mentioned before.
    I wonder if. when the batts are dying they can go in and out? Cold weather gives less electric current.

    Keep in mind, if the TPMS is dead, it could still have the old good reading in the Techstream data register. So what you could do is lower each tire pressure to make sure they responding...takes about a minute to see the effect. Maybe wait for a cold morning which would reduce current from the button batts. Just have to play with it.

    Just got me thinking about electronics, these TPMS must have the equivalent of a "Joule thief" which is a circuit that get's every last little bit of juice out of batts.
     
    #35 wjtracy, Mar 19, 2018
    Last edited: Mar 19, 2018
  16. Sezy

    Sezy Active Member

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    TPMS error seems to only happen on a 40F and above day when I'm eating my lunch in my car so it's running for at least 30 minutes. Shows on the dash while I have my OBD2 USB connected hooked up but as soon as Tech Stream starts it clears. I'll have to lower the pressure in one and see what tech stream does with a "real" tire issue.
     
  17. talonts

    talonts VFAQman

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    I had TIS 10.10.018 on my 2006 (built 11/05) last night, have had the light for months. After running a full Health Check, including entering the info for TPMS (current temp, expected low temp, expected pressures fr/rr, IIRC), it showed 3 reading pressure, one NULL.

    Today, if I have the energy (dealing with DTCs on BOTH the 06 and 04), I plan on setting the tire pressures to 50, 40, 30, and 20 to track down which one is dead. I have 4 sensors from a boneyard 08 that I will test one by one by tossing their IDs into TIS to see if they read with a binder clip or finger pressure. They were only $10, so if just one works, I should be golden. Then I'll see if I can use bar clamps to compress the tire bead enough to swap it out, get the bead popped back, and the tire filled, so I don't have to pay a shop to do it.

    My MIL's 06 also has the light, so this is a test run to see if I can track down which of hers are shot and if I can replace them in their garage in a quick visit.
     
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  18. Mendel Leisk

    Mendel Leisk Senior Member

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    Does Florida require operational TPMS, would failure put your car off the road?
     
  19. wjtracy

    wjtracy Senior Member

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    After all these years, my TPMS warning light is back on. Techstream reveals that at 12-years I have finally had my second battery go dead on the orig TPMS. However, the one with the binder clip is still working.

    On my Chrysler minivan (VW Routan variant), I had a pretty bad failure on a TPMS. The valve stem corroded thru and gave me a flat on the highway it gave out all of a sudden (at least I got the warning light). The tire store guy told me he sees that in the Chryslers. So this points out dead battery is not the only reason to consider replacing TPMS at some point 7-10 years old. I must say the Toyota OEM TPMS seem robust.
     
  20. RobH

    RobH Senior Member

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    One way to identify which TPMS is which is to park the car one side to the sun. After that side has baked a few hours, use Techstream to read the temperatures in the tires. The two on the sun side will be higher. Then turn the car 90 degrees with the sun at the front or back. Bake another few hours and you'll see which are front and back.
     
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