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Re: Low Tire Pressure Warning

"Difference in rotation speed"? Want to think about that a little? According to the little bit of physics I've learned your response is unhelpful and unaccurate.

If you take your Nissan to a shop with the right reader the pressure in each tire down to one decimal point can be read. The reading is very accurate, too, BTW.

The problem is in one or more of the tire sensors or in the reader/indicator module which triggers the instrument panel indicator.

Typically shops don't like to spend much time on diagnosing LTP warning malfunctions. My local dealer's service manager stated that he wished they had never put the damn things on the cars. According to him about 99% of the warnings were due to owner inattention to TP or to improper pressure adjusted by owners.

Last week, after the third time in the shop for my low TP indicator malfunction they reset the receiver/indicator module instead of simply adding air. Hopefully this will do the trick.

Normally these systems use the difference in the rotation speed to sense > the low pressure >> I have a brand new (bought in January) 2007 Versa. When I got it the >> tire pressure on all 4 was set at 40 PSI. >> I have left it at that value since the dealer/factory set it. >> >> Last Friday I took a short road trip, less than a hundred miles. About >> 2/3 of the way there the Low Tire Pressure light came on. I immediately >> pulled over and checked the tires. None seemed to be low, so I got out >> the pressure gauge and checked them. I found that the 2 front tires were >> up around 44 or 45 PSI. The rear tires were still around 40. I reduced >> the pressure on the front tires to 40 and started on down the road. The >> light went out and has stayed out ever since. >> >> I have made that trip twice before since I got the car but this is the >> first time when the temperature has been in the 70s. The last 2 times it >> was much colder. >> >> Does any body know what could have caused that? Does the system check >> more for a difference in pressure, rather than an actual pressure? >> >> Thanks for any help >> >> Bill Gill
Reply to
Butch Davis
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The company I work for manufactures tire pressure monitoring sensors and receivers (among other things). I thought I would give you a brief explanation of how they work.

The sensor is banded to the wheel inside the tire. There are different flavours of sensors, but usually they are either continuously transmitting or they have a switch inside that transmits only when the wheel is turning. These sensors measure actual pressure inside the tire. They transmit via RF to the receiver inside the car. The receiver is the "brains" of the system. It will throw a warning when a sensor fails or when a tire pressure is a certain percentage different from the others and/or it's initial value. The sensors have batteries inside them and will last typically longer than the life of the tire.

DS

Reply to
DS

I have looked the tires over, and looked on the web to try to find out about the way the system works. I found out that there are some that do work by difference in rotational speed. At least some of these tap into the ABS wheel speed sensor to check the wheel speed. If one is significantly different from the others it triggers the alarm.

There are several systems that use a sensor inside the tire to measure the pressure. They typically transmit the pressure to an on-board sensor for processing. This is very similar to the set up described by DS. It appears that the one used by Nissan is one that is built into the valve stem. The sensor is actually located inside of the tire.

I never did find anything that said exactly how the Nissan system works, other than the integral sensor. But I found at least one car that did have an over pressure warning included. It was set to trigger at 39 PSI. That would be in line with my having gotten a warning when my pressure gauge said the pressure was 44 or 45 PSI. Especially if my gauge happens to read high.

Some Nissan models do have the complete read-out on the dash board display. The Versa doesn't, just the pressure alarm.

I plan on getting a new, and hopefully more accurate, pressure gauge. That should keep me better informed on what is going on with my tires.

Thanks for all the good answers.

Bill Gill

Reply to
BillGill

Yes, difference in the rotation speed:

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I made clear " Not sure about this one in particular though. "

Whose response is unhelpful and INaccurate?

Through the years I have come to realize that pe> "Difference in rotation speed"? Want to think about that a little?

Reply to
AS

Interesting link. Did you not say " Normally these systems use the difference in the rotation speed to sense the low pressure in one of the tires?" Does "normally" not indicate that it is the norm? Does the norm not indicate the usual? Did you not notice in the discussion of the ABS based alternative that it does not work well enough at this time as it is too inaccurate to detect pressure losses of at best 20% and more likely 30% and that it has a set of additional proplems making it an unsatisfactory system? For example it will not work at speeds over 70 MPH.

In order for the rotational speed of a tire to significantly change due to pressure loss the loss must be large. After all, the tire circumference determines the rotational speed at a given speed, eh?

Thank you.

Reply to
Butch Davis

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