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TPMS Adventures: new lessons learned and insights gained

Discussion in 'Gen 3 Prius Technical Discussion' started by MrPete, Feb 6, 2024.

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  1. MrPete

    MrPete Active Member

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    After 13 years on the road, no surprise: my 2011 Gen 3 TPMS sensors have been going out. Here are lessons I've learned:

    Sensor Sourcing
    * YES, third party 315MHz sensors can be entered into a Prius and work well. I purchased MarsFlex PMV-107J (listed as compatible for Prius 2006-15).

    Install and Set The Easy Way
    * Discount Tire (nationwide in the USA) will separately replace a TPMS you supply for 2 x $5 tire dismount/remount fee. So, US$10/tire. (Free while replacing the tire.)
    * Discount Tire will also (at no charge) use their (BarTec) TPMS scanner to grab all four ID codes and push them into your vehicle. NICE! Here, you just go to the "Air Check" station and a rep will take care of you. It's actually quicker than getting tire pressures set up properly ;)

    Why Is It So Hard To Get Sensors To Be Recognized?
    * Is it on #1? First, understand that modern TPMS turns off when there's no extra pressure (ie not installed) and/or the sensor has not moved in a while. This is why the battery can last so long. (Used to be a strong binder clip would be seen as pressure. No more.)
    * Is it on #2? How else can a TPMS sensor be activated? The TPMS standard incorporates an "activation" signal, a simple 125kHz RF wave. Your Prius sends this signal when started. If monitoring with a good OBD2, you can watch the sensors go active! Appropriate TPMS scanners (like the Bartec and many more) can also do this. But just because it's active doesn't mean it is recognized by the car...
    * What's The Code #1? If your car doesn't know the ID codes of the sensors, it thinks they don't exist. First discovery: not everyone is diligent about ensuring the printed ID hex code matches the ID burned into the device! One of my four brand new MarsFlex sensors has outside ID DA9D2FD but inside is actually E816459. Without a high end scanner you'll never figure that out on your own.
    * What's The Code #2? My high end OBD2 reader -- OBDlink LX -- reads the wrong code from the Prius ECU for 3 out of 4 of my TPMS sensors! The numbers are off by varying amounts -6 to +7. At first I thought they were programmed wrong. Nope. Just bad OBD2 firmware/software. Toyota Techstream (with VXdiag for me) had it right. A source of confusion at least.
    * Good connection? Even with Techstream, if using an old/slow computer or slow link, it may not read/write reliably and you'll have a terrible time getting the codes entered. Doing it manually really isn't hard with a reliable link: Techstream/Prius gives you 300 seconds to enter four codes. Not that hard.

    How Accurate Is TPMS?
    * The TPMS standard specifies pressure as 2.5 * (an 8 bit unsigned number) in kPa. So if you read the pressure in kPa it will jump 2.5 kPa at a time. In PSI, that's almost +/- 0.4 PSI
    * The sensors aren't all that accurate either. I've not seen an actual spec, but various tests show variance of up to 3% of the reading. At Prius pressure of 38 PSI, that's another +/- 1.14 -- so now we're at +/- 1.5 PSI
    * Then there's the impact of temperature. From freezing to hot, that's another few PSI.
    * Speaking of Temp: TPMS reads temperature as (Celsius degrees) = ((unsigned 8 bit number) - 40)

    TPMS Battery Life?
    * My first set lasted 12+ years.
    * Recent verrrry cold weather made the last two look dead (-40C temp reading, and no pressure)
    * When it warmed up, one of the two stayed dead, the other revived.

    What Else?
    * Ignoring the fact that it gets the TPMS ID code wrong, the OBDlink app with Toyota option easily connects to TPMS and can dynamically display all TPMS data. Nice, easy. I'm sure other apps/OBD's do that as well.
    * NOTE that you can't necessarily tell the difference between a non-sending TPMS and a working one, while the car is in operation. The ECU remembers the previous reading for a long time!

    Should we care? TOTALLY up to you. Mendel gave up a long time ago on TPMS. Me? I drive in places that seem to generate slow leaks (nails, screws and more) so I appreciate knowing immediately when a tire is going bad. It can be VERY dangerous to drive on almost-flat tires. ;)
     
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  2. rjparker

    rjparker Tu Humilde Sirviente

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    They are allowed 20 minutes to read although typically it’s within minutes when you go over 20 mph. The time is to allow for sensor to sensor rf interference as they transmit independently. Other cars and flakey aftermarket headlight leds can interfere as well. The aftermarket LEDs can continuously interfere when on.

    Overall it’s very reliable and a whole set can be replaced for less than $100 parts and labor if you shop.
     
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  3. Mendel Leisk

    Mendel Leisk EGR Fanatic

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    Dang I didn’t get a chance. :ROFLMAO:
     
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  4. rjparker

    rjparker Tu Humilde Sirviente

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    We know you are tight with the Canadian Loonie (dollars) when it comes to safety gadgets.
     
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  5. Tombukt2

    Tombukt2 Senior Member

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    Mines on all the time in four cars I have brand new sensors and two of the four cars I just don't know where I put the numbers so I can manually enter them and tech. But in the meantime a friend of mine just said he bought a $50 tool that's made by a reputable company that'll make the things relearn automatically just walking up and pushing the button so I'm going to try that one of these weeks when I have time to go over to his house he doesn't get out all that much anymore and see He told me he has an extra one I can buy from him for 30 bucks if I want it It's worked on two of his Prius and two of his BMW motorcycles without issue He didn't know the numbers of the TPMS sensors or anything just stuff the Pacific sensors in the Gen 2 rode around with the light on for a week got this tool use the relearn feature light went out through the tool in the toolbox never again to see the light so far which is generally how it goes in the gen 2 until you have a flat I have all the flat tools in the car plugs and insertion tools slime etc I try to never use any of that stuff but I will put a plug in in a second on the side of the road If it's just a screw or a nail I'm out of there in 4 minutes I don't really like the fix a flat and the slime business I usually have that to help other people I would prefer not to put that in my tires I'm so far never have.
     
  6. MrPete

    MrPete Active Member

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    Makes sense. The actual sequence: 1) the tool is held to each tire, and reads the ID on that TPMS sensor (usual sequence: FL, FR, RR, RL but it doesn't really matter); 2) Plug the tool into the OBD2 port and it will upload the four ID's into the car.
     
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  7. CR94

    CR94 Senior Member

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    Mine went about 12½ years before I got the light, so at least they're consistent. I might follow Mendel's example, unless I can buy a set and have them installed and programmed for under $100 when next I need tires.
     
    #7 CR94, Feb 7, 2024
    Last edited: Feb 7, 2024
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  8. MrPete

    MrPete Active Member

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    Right now, you can do it for~ $20 a tire: $40 for a set of four sensors, $10 per tire to have them installed, and no charge for sensing the ID's and pushing them into your car. Doesn't get much better than that.

    This also means that you can swap Winter / Summer ID's at no charge as well, as long as every wheel has a sensor in it. :-D
     
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  9. GEN3PRI8

    GEN3PRI8 New Member

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    once installed how do you get them to show on the car, if my car originality never had them. where will the TPMS connect to display the pressure ?

    many thanks
     
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  10. Tombukt2

    Tombukt2 Senior Member

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    What do you mean if your car never had them Do you have a TPMS light on your dash that lights up and stays lit all the time on the car Yes No? If yes I didn't know that the generation 2 had an option to not have them but be that as it may If it doesn't you don't have the options installing the sensors will make nothing happen If your car has TPMS and you have a TPMS orange light on the dashboard and the car is wired for TPMS radio frequency and all that then you're in good shape You mount the sensors and you follow the instructions some of them you have to pump up and then take out half the air and then pump them back up to some such nonsense. Or you can buy a tool that generally cost about $50 or you can take it to a tire shop like discount tire wants the sensors are mounted and on the car they have a tool that will relearn each sensor to the car doesn't really matter the sensor preferably there the Pacific branded ones like we talked about the other day here but if not a lot of these tools will turn on the learn mode and with the car on they'll register to the car and the learn mode essentially or you'll use software like Toyota tech and enter the numbers manually in there and push enter and so on and so forth and do that for each set of numbers depends on what you have available to you usually with most people that go to the tire store it's just much faster and if they don't have to mount anything they're already mounted. All they're going to do is run their wand over the sensors and boot the car etc and do that for all four wheels and the light will go out then everything will work as per your owner's manual that might be in your glove box.
     
  11. MrPete

    MrPete Active Member

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    There are three separate elements to vehicle TPMS:
    1. A control unit ("TPMS ECU") with RF transmitter/receiver and wired connection to the vehicle internal communication
    2. Sensors in each tire
    3. Some kind of built in display (on Prius it's just an LED icon in the dash) that's driven by the ECU (#1 in this list)
    Since TPMS is not required in Japan (nor Canada last I checked), at least some of the above may be missing.
    #1 above may not be easy to add, but should be easy to detect with Techstream or a good OBD2 like OBDlink LX. (If those can't find the TPMS system at all, it's most likely missing. See below on that. :) )
    #2 is easy to add as I described above
    #3 has many options if missing, depending on what you prefer...

    If you don't need hardware in the car itself, a good OBD2 app or Techstream can read the data whenever you like. No dash LED required.

    If you want a display, you can do better than the good/bad LED indicator. There are displays available (and even entire independent TPMS systems)
     
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  12. rjparker

    rjparker Tu Humilde Sirviente

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    Being from the UK your best bet is to buy a separate tpms display since your car won’t have the rf receiver, tpms ecu or proper software.
    IMG_4236.jpeg


    https://www.amazon.com/Hlyjoon-Receiver-Pressure-Monitoring-Internal/dp/B07TBKYH76/ref=mp_s_a_1_3?crid=2QSTS082M7OYK&keywords=tpms+receiver&qid=1707680680&sprefix=tpms+receiver,aps,245&sr=8-3
     
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  13. GEN3PRI8

    GEN3PRI8 New Member

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    thank you for this mate.
     
  14. Tombukt2

    Tombukt2 Senior Member

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    Boy I can't even imagine doing this to my Corollas supras etc. what I would consider is adding a true heads-up display in some of my other vehicles That's very inexpensive now but adding TPMS oh no I checked my tires too off and I have a hose hanging at a compressor that I parked next to so the last time I had a flat was maybe in the mid '80s seriously so we don't really do flats a lot and we do go off-roadways all the time It is nothing for my vehicles to be running down a fence line no problem at all haven't had a flat out in the woods in my cars ever that I can remember I've had power sports equipment tires blow up get things in them what have you but never in any of the cars or the road cars.
     
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  15. maurakl

    maurakl Junior Member

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  16. Tombukt2

    Tombukt2 Senior Member

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    Yeah all of those tire sensors work like that even the factory originals for $49 for a set of four work the same way if you have a TPMS relearn tool to strike up the relearn with the sensors and the vehicle so yeah pretty much anybody can buy the tool to do this there's a Toyota tool that some company makes with a yellow logo that only costs about 50 bucks you can buy them online that does just only that or you can simply remember or write down all four identification codes and enter them in manually in your Toyota software If you have such a thing even the AP200 I think may be able to do this or it will at least show you that the sensors are mounted and what their numbers are but the AP200 can't strike up a relearn You have to have like the MX808 or other tools that are capable of TPMS work or not bother with any tooling and let the tire center do it for the $10 my goodness makes sense everybody's not going to go out and buy every tool when they do this once every 13 years