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Does Model S use Tire Pressure Sensors?

Discussion in 'Model S: Driving Dynamics' started by mknox, Oct 26, 2012.

  1. mknox

    mknox Well-Known Member

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    So I'm reading through the Owners Guide and come across this:

    ScreenShot001.jpg

    What strikes me is that this is almost identical to the way the TPM works in my Pontiac Vibe. The Vibe has no wheel pressure sensors and relies on the ABS system to detect a wheel spinning at a slightly different RPM compared to the others as a result of its diameter changing due to under inflation. The reason for the 10 minute drive after re-inflation is so that the system can re-calibrate itself via the ABS sensors.

    It has worked for me on the Vibe, but you don't know which tire is the problem until you get out and check. In my view, it's inferior to having wheel-mounted sensors, but it does work.

    I wondered why Model S has no display for individual tire pressures (like my Cadillac CTS does) and this may be why.
     
  2. clea

    clea Member

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  3. mknox

    mknox Well-Known Member

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    Interesting. With discrete sensors, there should be no requirement for a 10-minute drive to re-calibrate. I had a slow leak on my CTS and as soon as I pumped it up and the pressure was back in range, the light would go out - even with the car parked.

    If they do have sensors, I wish they had a way to show the actual pressure in each tire on one of the screens.
     
  4. wycolo

    wycolo Active Member

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    #4 wycolo, Oct 26, 2012
    Last edited: Oct 26, 2012
    Under US regs since 2005 (or is it 2006?) all car must have TPMS. TM has chosen to have the sensors in the rims. :rolleyes:
    --
     
  5. mnx

    mnx 2013 P85

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    but not actual sensors in the tires. my 2011 bmw uses the abs system as mentioned above.
     
  6. Doug_G

    Doug_G Lead Moderator

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    The TPMS sensors have a fairly slow update rate. It can take minutes for the signals to get through to the car. This is true for my Roadster and I've also seen it on Nissan/Infiniti cars.
     
  7. pete8314

    pete8314 Vendor

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    Same in my Audi A5. And once I've filled all the tires to the 'correct' pressure, I have to tell the car that the pressures are good, and off goes the warning light. I know I paid for TPMS sensors when I had my tires replaced, but it sure sounds like mine uses the ABS system (?)
     
  8. mknox

    mknox Well-Known Member

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    My Cadillac's are instantaneous. I can hook up my 12v compressor and just watch the display go up until I'm at the desired pressure. I always check with a manual tire gauge, and the readout on the dash is spot on.

    - - - Updated - - -

    So this is interesting...

    The manual suggests (to me) that the Model S is using an ABS algorithm to monitor tires, but as clea points out, winter tire sets on the TM site specifically mention pressure sensors.

    If Model S has the sensors, it seems odd that you have to get out and manually check the tires when they could display the culprit and it's actual PSI right on the screen. My CTS does this with its sensors.

    I wonder if this is a software thing. Perhaps they've implemented the ABS algorithm "for now" but have the sensors and receivers in place and are just waiting for some future firmware update???

    Doug_G points out that some TPM sensors (Roadster, Nissan cited) are slower in responding than the ones I'm familiar with in my Cadillac, so maybe there is some other TPM system that's in between the systems I have experience with (Pontiac Vibe and Cadillac CTS). Maybe my "fast responding" sensors are more conducive to reporting the status of each tire, but the "slow" ones are not keyed to each wheel position and just let the system know there is a low tire "somewhere".
     
  9. dsm363

    dsm363 Roadster + Sig Model S

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    On the Roadster, you can see each individual tire pressure but it does take a few minutes to report at first for some reason. They will tell you you have low pressure somewhere then you can look at the screen to tell which tire it is. On the Model S, they have hidden the individual tire pressures for some reason.
     
  10. TEG

    TEG TMC Moderator

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  11. Doug_G

    Doug_G Lead Moderator

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    Probably so that they don't have to resynchronize the TPMS when you change tires, etc. My old Nissan would report four tire pressures, but it wouldn't know which was which. Every time you started the car the pressures would appear in different random slots. The slots weren't identified as to which tire it was, so that didn't matter a lot.
     
  12. mknox

    mknox Well-Known Member

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    That's interesting. My car tells you which tire is which, but you do have to re-program it whenever you rotate tires. The dealer has a tool to do it, or there is some convoluted process for the DIYer where the car will honk the horn and blink a front or rear turn signal to let you know which wheel you're setting up.

    Perhaps Model S has a Nissan-like system, and since it doesn't know which tire is which, there is no point in reporting it on a screen.
     
  13. Doug_G

    Doug_G Lead Moderator

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    That's what I'm guessing. The Roadster system was a pain in the butt for both customers and their service people. Still, they could at least list the pressures rather than hide them. That way you can judge for yourself whether it's a critical issue that needs to be dealt with NOW, or something you can fix when you get home.
     
  14. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    GM does the same thing, the cars detect the tire pressure changes and you go in order to reset them. SOP for those who can't program via the computer is to over-inflate by 3 psi per tire, then go in order and let the 3 psi out while the computer monitors. That way you ensure properly inflated tires and program the system correctly.
     
  15. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    That won't insure properly inflated tires. TPMS alerts when the tires are 25% low. If the tires are that low damage has likely already occurred. You want to calibrate them so that they alert when the are no more than 3 psi below the pressure you want to run them at.
     
  16. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    Sorry, Jerry, perhaps I wasn't clear. The 3 PSI is the amount of air that you release when you're telling the vehicle which sensor is on which tire. If nameplate pressures show 35, you inflate each tire to 38, then reset the TPMS and teach it which sensor is which by draining that extra 3 PSI. I don't believe that "calibration" can be done by an end-user (certainly can't do it on my mid-2000's Suburban).
     
  17. mknox

    mknox Well-Known Member

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    That is correct. GM cars will blink one front or rear signal light to let you know which tire to set up. You can then either add or bleed 3 PSI from that tire and the car will "learn" the wheel's position and honk the horn. It will then blink the next turn signal light and you repeat the process. After that, you can adjust the pressure to your liking.

    The dealer can do it much quicker with a hand tool. The above process is for the DIYer.
     
  18. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    Okay. On Toyotas you can set the pressure by inflating the tire to enough over the pressure you want to maintain so that it will alert when you are only down a few psi from your target pressure. It doesn't care about the vehicle placard pressures.
     
  19. contaygious

    contaygious Active Member

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    It's easy on 03 Infiniti. Calculates and shows each tire and psi when you start the car. Audio and visual alert if under 25 psi. No update needed after rotation. Not sure why the newer cars have issues with this.
     
  20. mknox

    mknox Well-Known Member

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    How does it know, for instance, if you swap front to rear during a tire rotation? The sensor in the wheel is keyed to a location (i.e. front right) on the car, so if you move that wheel to another location, how does the car know where it is if you don't update??? Or perhaps, does Nissan just show 4 PSI values but not where on the car the tires are? (My car will tell you each wheel location and the corresponding pressure).
     

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