How Does It Work

[GLF]

My wife has a newer Pontiac Grand Prix. She told me the tire pressure warning came on. So....I checked the tire pressures. One of the tires was 10lbs less than the other three and had a bolt in it. I took the tire in and had a patch put on it and all is well now.

How does the computer sense that the tire pressure is low? Someone at her work told her there is a sensor in the valve stem. I find this hard to believe, as this would be an expensive valve stem

[Take Six...]

It could be in the valve. That was one of the earlier versions. It had batteries and sent RF signals to a receiver tied to the computer. A less expensive and more widely used version works on sensing tire rotation. A slight drop in tire pressure would reduce the number of revolutions the tire spins. The unit is calibrated at the factory after the tires have been inflated to their proper pressure. The latest types do montior tire pressure and energy to run it is through inductive energy produced as the wheel spins. A magnet passes by a copper band to produce the minute current need to run the RF sensor. I've quoted building automated machinery to assemble these sensors. New government standards require these devices on new cars.

[Satisfaxion_Gauranteed]

Many cars utilize a sensor in the brake assembly that monitors brake rotor speed. It's pretty simple and doesn't have a drastic effect on cost of the car or replacement parts.

[Dv8oR]

Their called direct and indirect systems.

Stated earlier, some (mostly GM) are monitored by the ABS system and does monitor wheel speed.-Indirect.

Direct systems (Chrysler, Jap models) do have an actual valve stem to the tune of about $45.00 a piece- Monitored by RF sends a signal back to the computer telling actual tire pressure. I have a hand held tool (to the tune of a couple of grand) for detecting if these sensors are active/functioning, and also recalibrate.

Could be a Federal mandate that all cars will have them by 2008 from what I last read/worked on.

Also-Remember my pitch on Nitrogen. This will be a federal mandate as well.

Someone also said the non direct is pretty simple. Acutally on the GM's, if a wheel speed sensor goes out, your replacing the entire hub assembly-to the tune of $350-400 bucks a throw. Not exactly simple.........

[GLF]

Thanks for the information. I do not believe its in the valve stem. I could reset the warning messsage while the car is sitting still. If I drive the car it comes back on.

[Dv8oR]

Theres:

Resetting the Light.

and

Reinitializing the system.

Sounds like you might need option b.

Make sure the tire pressures (printed on the driver door label) are consistent all the way around.

[Satisfaxion_Gauranteed]

Also-Remember my pitch on Nitrogen. This will be a federal mandate as well.

On the nitrogen thing, I really struggle with this for several reasons. First, unless the application is a highly performance designed race car with suspension systems tuned to small fractions running on super speedway race tracks, then the 5% difference of compressability at elevated temperatures will not even be noticed by the average driver. It will deffinately not have an effect on fuel economy or perfomance on a passenger vehicle where forces and conditions during one mile of operation vary more than that of a 400mile race.

Second, the claim of improved saftey due to less tire degradation from contaminated air doesn't sit well with me. Oxygen, moisture, oil, UV light, etc is all around the perimeter of the tire. The degradation effects of those items doesn't do more damage to the tire than normal wear. Also, tire pressure affects the handling of the vehicle, not what is inside the tire.

Third, the leakage claims. Nitrogen is smaller on the molecular level than Oxygen. However, if there's an inperfection of materials of the wheel large enough for O2 to get through, than you can expect N2 to do the same. Also, from my experience of testing gas compressor seals for leakage, there has yet to be a single difference in leakage values from air to helium to nitrogen to argon. It has yet to happen because no standard manufacturing process is perfect enough to make flaws that 1 oxygen molecule would go through without allowing a nitrogen molecule.

Fourth, rapid expansion/temperature increases due to contaminants is claimed to be eliminated with N2. I can see this IF the air going into the tire is at saturation for moisture or any other contamination. However, a compressor filter is cheaper than the process used to seperate N2. Clean, dry N2 is going to act very nearly identical to clean, dry air, particularly in automotive aplications.

Fifth, nitrogen is claimed safer because it does not support combustion. This is absolutely true. However, the whole tire is surrounded by plenty of oxygenated air to support combustion.

Sixth, nitrogen is claimed not to heat up as quickly as air. This is simply not true. The specific heat ratio(from my fluid mechanics book) of Nitrogen is the same as air (1.4 for both). Specific heat is the property of a fluid to give/take heat.

On a race track with a custom made car not meant to carry passengers is one thing. In automobiles mass produced for the public is another. For the average driver, the advantages of nitrogen certainly don't matter enough to pay extra money.

my 2cents,

[Dv8oR]

This will be a federal mandate as well.

There's lots of things the feds do that don't have to "sit well" with us

T

[Satisfaxion_Gauranteed]

There's lots of things the feds do that don't have to "sit well" with us

T

You hit the nail on the head! It'd be a shame to tackle some of the very tough issues that actually put a real strain on the working class(i.e. health care, retirement, civil liberties, education, clean energy(not batteries), wars, science and technology vs morality, etc)

Oh well, at least there's still good fish in the lake!

At some point and time, the tough issues will have to be addressed.

I guess if it were easy, anybody would do it.