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Tire Pressure Sensor in Spare?

Discussion in 'Gen 3 Prius Technical Discussion' started by rachaelseven, Aug 22, 2009.

  1. rachaelseven

    rachaelseven New Member

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    Does anyone happen to know if the Gen III spare tire has a tire pressure monitoring sensor installed? Or if it is supposed to have one? Just had a look at mine and it appears to have a regular valve and not a TPMS sensor. Also, the computer printout my dealer gave me that shows the registered ID codes for the sensors only shows 4 - there's space for a 5th one, but the information is blank. I wonder if a 5th one can actually be registered? Is it worth it to register a sensor for the spare for the peace of mind of knowing it still has air?
     
  2. Glider

    Glider New Member

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    The manual (p343) says that the compact spare tire does not come with a pressure warning valve and transmitter. I think that's the spare tire I got with my car - not sure about yours. Also, I remember the service rep saying it didn't have one.

    I don't remember getting any computer printout when I bought the car. Was this after you had it serviced?

    - g
     
  3. Glider

    Glider New Member

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    Sorry, its p434. :)
     
  4. rachaelseven

    rachaelseven New Member

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    I knew I should have RTFM... again. Must have missed that on my first time through - thanks for the page reference.

    The printout was from when they were setting my custom functions before the delivery. The tech let me look over his shoulder and as we were exploring together (it was the first Gen III he'd hooked up to), I asked him to print the TPMS page. I figured it might be handy to know the ID's of the sensors for future reference (like come snow tire time).

    Rachael :)
     
  5. bluetwo

    bluetwo Relevance is irrelevant

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    That was good thinking Rachael. TPMS sensors are actually far more of a PITA than they are good, just speaking in terms of percentages. The number of people they've inconvienced has got to be far greater than the people who have actually needed a little light to come on and say they dummy you have a low tire.....

    They are just as much a pain to people who want to have an extra set of snow tires as they are to people who put performance rims and tires or bling/bling wheels on their G ride. Usually, from what I've read about most models, it only takes a few minutes of riding around after the spare is removed and stowed again for the regular tire pressure monitering system wheel to communicate with the ECU and turn that pesky dummy light out again.
     
  6. Glider

    Glider New Member

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    Sorry, forgot to mention that this is a very good point. I rarely check my spare (dumb me) and it wasn't too long ago, on another car, that I asked them to use the spare as part of the tire rotation and had them inform me it had something like 10 PSI in it. A flat spare isn't much good is it??

    - g
     
  7. rachaelseven

    rachaelseven New Member

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    Exactly what I was thinking. And I'm honest enough with myself to admit that I will never check the pressure in the spare. I mean seriously... it's all I can do to check the pressure in the 4 on the car... I drive the thing, ya know? So I thought a 5th sensor would be a nice way to know that the spare is still a spare rather than some dead weight in the back. Unfortunately, everything I've been able to unearth so far indicates that only 4 sensors can be registered to the system, despite the apparent space for a 5th on my printout. As an interesting side note, the Techstream printout also makes reference to a 2nd set of sensors and a switch between the two - also features that are unfortunately not included on the Gen III at the moment, but were at least thought about when they created the TPMS ECU. Perhaps we'll see an update in the future.
     
  8. jay_man2

    jay_man2 jay_man_also

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    The bad thing about the spare is that the the way it's stowed the valve stem is face down, so it's a major PITA to pull the cargo box out, pull the spare out, then check the pressure.
     
  9. rachaelseven

    rachaelseven New Member

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    Like I said, you have to be a heck of a lot more dedicated and responsible than me to make that check a regular occurrence. I'll make the dealer do it at oil changes or something :S
     
  10. jay_man2

    jay_man2 jay_man_also

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    I used to check tire pressures every Saturday morning, along with the fluid levels and battery indicator (the green or blue eye on a 12v battery). With the advent of TPMS, I'd completely fallen out of that very useful habit, but I'm trying to work it back into my weekend routine.
     
  11. qbee42

    qbee42 My other car is a boat

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    If you flip the car upside down it's much easier to get to the valve stem and check the pressure. ;)

    Tom
     
  12. stream

    stream Senior Member

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    I check my tires monthly--give it a try--weekly is probably a bit overkill, and the monthly schedule is more likely to be performed. ;) The TPMS threshold is so high (8 PSI as I recall) that I wouldn't want to rely on it, short of when you get a flat tire.
     
  13. stream

    stream Senior Member

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    You could attach an extension hose to the valve stem:
    Chek-a-spare, Check-a-spare, tire gauge guard

    They make excellent quality pressure gauges--here's the one I use:
    Dial Tire gauges
     
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  14. tumbleweed

    tumbleweed Senior Member

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    The spare holds air pretty well, I usually check mine once a year and put 65 or 70 lbs in it. If I need to use it I'll check it and let a little out if needed.

    My cynical side says the reason the TPMS sensor ID can't be changed by the car owner or even the tire shop is because dealers have pressured manufacturers to have a lot of simple stuff on the car that only they have the software to change. That way the dealers can charge an hours expensive labor to shut off the annoying backup beeper or change the sensors, which should take no more than 5 min. :mad:

    Unfortunately it works because to many customers think "Toyota knows best" or "if the dealer said so it must be true".

    OK, now I'll climb down off my soap box.
     
  15. Boo

    Boo Boola Boola Member

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    AFAIK, a tire pressure sensor in the donut spare wouldn't work because the 4 regular tires have a recommended psi of around 35 psi, while the donut spare has a recommended psi of around 60 psi(?).

    So if the Tire Pressure Monitoring System were set for the 4 regular tires' 35 psi, and the donut spare had a sensor in it, the donut spare would have to be at around half of its recommended 60 psi in order to trigger the TPMS warning light.

    Although this would be somewhat useful, I'd rather save the $100+ cost of a tire pressure sensor in the donut spare.
     
  16. jayman

    jayman Senior Member

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    There are some vehicles that allow you to register two sets of TPMS id's, but AFAIK these are luxury import SUV's. The principle behind the luxury import SUV allowing two sets of TPMS keys is that one set can be used for the normal tires/wheels, the second set for either off-road or studded winter tires on separate wheels
     
  17. qbee42

    qbee42 My other car is a boat

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    Kind of odd too, when you consider that the additional cost in electronics is next to nothing. The logic and memory requirements are trivial.

    Tom
     
  18. Boo

    Boo Boola Boola Member

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    Probably in the future, TPMS will have at least 4 settings -- one for each tire -- and show exactly which tire is underinflated.
     
  19. stream

    stream Senior Member

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    Some TPMS systems show the actual tire pressure for each tire.
     
  20. Boo

    Boo Boola Boola Member

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    That would be ideal. Which car has that now?