Q1: Where is the tire pressure sensor (usually) located ?

Q2: How does it connect to the ECU, I see no electrical connection going to the wheel?

Q3: Why do dashboards not tell you specifically which tire has low pressure rather than one light for all the tires?

Q4: Do most vehicle's factor the spare when checking tire pressure or only the active four?

  • 2
    Just a note (which may have been stated in the answers, I haven’t read that far), some TPMS do tell you the actual pressure in each individual tyre and which one is low. I have a Nissan X-Trail that does so.
    – Darren
    Dec 12, 2022 at 7:32

1 Answer 1


There are two basic systems that monitor tire pressure. There are active and passive systems. The active systems use a sensor and transmitter inside the tire. Older systems attached the sensor to the wheel with a band clamp inside the tire, newer sensors are part of the valve stem and are again inside the tire. The sensors communicate wirelessly to the control module. More complex systems assign an ID sequence to each sensor and knows each location after programing. This means after rotation they must be relearned to their current location. Less complex systems just indicate that one of the tires have lower than normal pressure. Passive systems use the wheel speed sensor to calculate the difference in wheel speed of a low pressure tire. I can only guess that with this system four underinflated tire might not activate the warning system. Most systems do not monitor the spare. Some newer vehicles also include trailer tire monitoring as an option. There are also standalone systems that communicate wirelessly to a separate receiver in the tow vehicle.

  • if my truck is 2007 Toyota, do you think this is old or new system?
    – amphibient
    Dec 11, 2022 at 21:25
  • @amphibient - What do you mean by "old or new system"? The only vehicle I'm aware of (I'm sure there are others) using an active system which attached by band to the wheel was the Corvette. This was one of the first systems on the market and they employed it because they used run flats on them, and so they wouldn't have to carry a spare tire. Most TPMS's are attached to the valve stem. If your truck has a TPMS, look at the valve stem. A giveaway is usually these have a nut which secures a metal stem to the wheel from the outside. If it DOESN'T have this, it doesn't mean that's not what it is Dec 11, 2022 at 21:40
  • I am referring to what he is referring to by old and new
    – amphibient
    Dec 11, 2022 at 21:48
  • 2
    @amphibient - So there's not any misconceptions, the battery, sensor, transmitter reside INSIDE the tire, but are attached to the valve stem. Here's a Toyota one. No nut, it appears. Attaches into the rim just like a regular valve stem. Dec 11, 2022 at 22:18
  • 1
    @DavidLindon - The active kind is an RF transmitter which is battery powered. Your Jag uses an active type sensor. And you'd be surprised at the difference in height being 6psi shy of full will cause, which in turn causes wheel speed changes. Just because it doesn't look like it's shorter, doesn't mean it isn't. Even minor changes in pressure can change the rotational distance of a tire. Dec 12, 2022 at 11:04

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