Tire p Monitors: How Done ?

Hello,

What's the principle behind the tire pressure monitors that display tire p on a dashboard display on so many new cars now ? Is there a small radio transmitter and p transducer in each tire ? Or,... ?

Hard to believe that is how they do it, due to the cost.

How is it done ?

Thanks, B.

Reply to
Robert11
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Two methods. First is exactly as you describe. Second, cheaper method uses the wheel speed sensors for the ABS and just lights a light when one wheel starts turning consistently faster than all the others (e.g. TP has dropped at that corner enough to affect the rolling diameter of that tire/wheel combo.)

nate

Reply to
N8N

__________________ The description of the second method makes a lot more sense. How sensitive is it though - down to 3psi difference?

Another variable that might *trick* the wheel revolution method is that different tire brands(and models within brands) possess different rubber compounds & makeups. This in turn might affect how the tire reacts as pressure reduces in a leaky tire. A higher level of something called "hysteresis" - related to the stiffness of rubber - might also lead to a delay in triggering of the low-pressure dash indicator until the tire is more than 5psi under spec.

-CC

Reply to
ChrisCoaster

There are two common methods used. One uses radio transmitters in each wheel. Just as you stated. That is the common method used on many vehicles in fact. The transmitters are either inside a housing and part of the valve stem assembly OR they are clamped in place in the dished area of the wheel. Both were used by factory and aftermarket systems. Also most of the vehicles that use this system don't have a sensor in the spare so you end up with a warning light if you don't buy a sensor if you rotate the spare as well.

The second most common method uses the ABS sensors to read individual wheel speed and if one sensor starts to speed up(due to pressure loss while moving) or the speeds don't match after the systems self test is complete after start up it turns on the warning light for that tire.

The first system is a bit faster in reaction and it allows you to monitor actual pressure real time. BUT every time you rotate the tires you need to get them reset to the new position AND if you change the tire size/pressure you need to reset the systems monitors to match the new numbers. So say you insist on running your tires at 60 PSI but the factory recommends 32, it will trip the warning lights on as well.

The advantage of the second system is that you can run any tire and any pressure as long as they all match, and rotation is easy. BUT you give up the ability to monitor the tire pressure inside the vehicle (no big deal unless your anal about that type of stuff). It is also cheaper since the sensors run from 50-150 bucks each and a boneheaded move with a tire machine can destroy them.

Reply to
Steve W.

Additionally there are aftermarket TPMs with transmitters that install externally on the valve stem. These are available in models that support more than 4 tires + spare, i.e. dual rears, trailers up to tandem semi.

Reply to
Pete C.

I believe in the case of the ABS sensor method, you can reset the warning light after you've rotated your tires and set them to the proper pressures and it will "relearn" what the correct speeds are supposed to be relative to each other; it'll only throw the light again when something changes.

I don't know how sensitive that method would be; i'm certain that it would be dependent on whoever programmed the software. I know that my '05 Impala uses that method, but the only two times I've seen the light come on were when the tire was well and truly flat. (1st time, ran over a piece of angle iron in the road and punched a hole in the tread; tire held on the way to work, but when I left again it started to go flat as I was driving. 2nd time I picked up a screw.) Both times when i got to a safe place to stop, the rim was about half the distance from the road that it normally is. I haven't ever had a true slow leak on the car so I don't have any personal experience with being able to figure out when exactly the light comeso n.

nate

Reply to
N8N

My 2001 Mustang did not have a tire pressure monitor, but it di have ABS. At one point I had a slow leak in one of the rear tires. When the pressure dropped by about 6 psi, I'd get an ABS fault code. Bringing the tire back up to pressure turned the light off. This was very consistent over a peroid of about 2 weeks while I waas waiting for new tires.

Ed

Reply to
Ed White

My 2006 Nissan Frontier has sensors in the wheel (but not one in the spare). Rotating the tires does not require a reset - but my system does not identify which tire is low (and all tires require the same pressure). I've had the warning light illuminate once in 2.5 years. Replacing the tires (at Costco) did not cause any problems. My SO's RAV4 also uses sensors in the tires, but does have a fifth in the spare tire. It does not require a reset after rotation either. But, again, it does not identify which tire is low. The first time her light came on, she was baffled because all her road tires were up to pressure. After I had her check the spare, she found it was low. Inflating the spare to the recommended pressure turned the light off.

Ed

Reply to
Ed White

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