Tire Pressure Indicators

[Ranger]

Those of you who have them, what are your impressions? I don't find them very acurate. I use an electronic digital tire pressure guage and today I checked my tires. Put them all at 32 PSI. Went out to dinner an hour later and pulled the pressures on the dash. The pressures read 29/29/30/31. I'm not impressed. I guess all I can use it for is to alert me if I get a nail in one as I found in my wifes tire when I checked hers. One was at 15 psi. The tires are only a couple of months old too. She's a nail magnet.

[Bruce Nunnally]

Not enough controls in your experiment. What temperature were the tires at when you filled them? What temperature an hour later?

My wife's last nail/blowout was at a fast food joint at least, so I got a large soda while I changed to the spare.

[Ranger]

Well the car sat for several hours since I last drove it to let the tires cool down before I set the pressures. I did not think to use the digita infered thermometor.

[Patrick7997]

They were within a couple pounds on my C5... and it sounds like you are close to that....

Bruce is right though, lots of things could cause a +- 3lb difference....

The C5 seemed to read 3 lbs less than my tire guage, which again, oddly is very close to what you are seeing.....

My impression was it wasn't supposed to be an exact system anyway... The Corvette had no spare, and allegedly, the run flat tires were so good, they felt it was possible for the driver to be unaware that he/she had a flat... thus, tire pressure monitors, to alert you that you have a flat.... that was what my impression of the system was...

[JasonA]

It's pretty much standard practice these days that if the car has runflats, it also has a tire pressure monitoring system.

I'd agree with Ranger's initial impression that something seems fishy. The tires should warm up after a drive if anything, instead of cool down. I'd think the ambient temperatures would have to have gotten real cold for the tires to drop that quickly. Ranger, were the tires cold when you initially filled them to 32, or were they warm at that time already? If they were cold when you filled them to 32, and the TPM system read 2-3 psi lower after a drive, it certainly sounds like they're not very accurate. Check the pressures on the TPM right at the time you fill the tires -- that would at least rule out temperature swings.

The TPM system on my brother's 1999 Corvette seems pretty close. Within 1 psi of my gauge.

[davedog]

mine are usually with in 1 or 2 psi, some times they are dead on, but they often fluctuate. I don't think they are meant to be an exact science, just something to give you a rough idea of if there is a problem.

2005 SRX

-dave

[Ranger]

mine are usually with in 1 or 2 psi, some times they are dead on, but they often fluctuate. I don't think they are meant to be an exact science, just something to give you a rough idea of if there is a problem.

2005 SRX

-dave

My thoughts exactly. That is how I will treat them.

[KHE]

I would tend to believe the car tire pressure sensors vs. a cheap handheld gage. I doubt the handheld gage's calibration can be traced to known standards.

[GreenMachine]

I have a digital gauge that I bought at autzone, don't really trust it, gives me some strange readings from time to time, the good old kind that the little end shoots out with the penclip is good enough for me.

On another note did you check the tires with the tire guage to confirm that the onboard was wrong?

I've also heard you can re-calibrate them if need be.

Another thing might be the air from the compressure you used may have been hotter/cooler more humid than the air you put in. The differfrance between tires could be from driving more left turns than rights and vice versa, front on FWD cars tend to always run hotter too.

[Bruce Nunnally]

TIP: The TPM sensor is more precise than consumer-grade tire pressure gauges. It may be necessary to explain this if the customer routinely mis-inflates tires using a gas station gauge.

Courtesy: http://www.hunter.com/pub/undercar/TECHLINK/index.htm

GM TechLink Magazine Update

January 2003

Tire Pressure Monitoring System Information Addition

A tire pressure monitor (TPM) system is used on Cadillac DeVille, Seville and Chevrolet Corvette. This system was discussed in the November 2000 TechLink. This is a brief review, because there is some new service information available.

Components

There is a separate sensor/transmitter in each wheel. The TPM system shares the receiver with the keyless entry system. Data from the receiver is displayed on the instrument panel, using the driver information center (DIC).

Sensors

The sensor, with built-in valve stem, is inserted from the inside of the wheel, through a hole in the rim. It is retained by a nut (4 N.m, 35 lb. in.) and is sealed by a grommet. A lithium battery with a design life of 10 years powers the sensor.

Each sensor is coded differently. This permits the receiver to determine exactly which tire is over or under-inflated.

Operation

The sensors operate only above 20 mph (32 kph) and transmit once per hour when parked, to preserve battery power.

If the pressure in a tire rises or falls outside the calibration limits, the condition is displayed by the DIC. The low limit is 24 psi (168 kPa) and the upper limit is 39 psi (272 kPa).

Service

The sensors are lightweight, only about an ounce (28 g), and this small weight is easily accounted for during normal tire balancing.

The sensors are mounted within the well of the rim. It’s important to be careful when using a tire-mounting machine. The sensor could be damaged in two ways: either by (1) direct contact with the machinery or (2) by the bead of the tire as it is forced over the rim.

Use care when using tire machine.

Consult tire changer manufacturer’s support material for proper mounting procedures.

Sensor ruined by tire mounting equipment

The valve stem cap is made of aluminum and the valve core is nickel-plated to resist corrosion. The end of the stem serves as the sensor’s antenna.

TIP: Do not replace either the cap or the valve with standard parts. This will interfere with the sensor’s ability to transmit.

TIP: The TPM sensor is more precise than consumer-grade tire pressure gauges. It may be necessary to explain this if the customer routinely mis-inflates tires using a gas station gauge.

Receiver Programming

The receiver is programmed at the factory to recognize which sensor is at each wheel location. If tires are rotated or a sensor is replaced, the receiver must be reprogrammed, following SI procedures.

If the receiver is not reprogrammed, the system will continue to report the correct pressures, but will assign them to the wrong locations on the vehicle.

TIP: There are two reprogramming methods. You must use the J-41760 magnet when a new sensor is installed. During tire rotation, you can use either the magnet or your Tech 2.

J-41760 Magnet

Magnet Method

You will have only one minute between horn chirps, and five minutes overall, to complete the procedure once you start.

With ignition on, engine not running, press both lock and unlock buttons on the key fob. A horn chirp within 10 seconds indicates that the receiver is in programming mode.

At each wheel, hold the J-41760 magnet over the valve stem until the horn chirps, to force the sensor to transmit its code. You must follow this order: LF, RF, RR and LR. The horn chirps twice to indicate completion.

Scroll through the DIC readout to verify all four pressures are displayed.

Tech 2 Method

With the TPM Reprogramming procedure on your Tech 2, you can command each sensor to its new location. As long as no new sensors are being installed, the magnet is not needed.

Scroll through the DIC readout to verify all four pressures are displayed.

Instrument Cluster Module Programming

On the Seville and DeVille models, if you disconnect or replace the IP cluster, the IP module must also be programmed to enable the TPM option. If this is not done, the DIC will not be able to display information from TPM receiver.

Follow this path on your Tech 2.

Body

Instrument Panel Cluster

Special Functions

Set Options

Tire Pressure Monitor

Read the instruction screen, then press Continue

Scroll to highlight the Tire Pressure Monitor

Press the Enter key to place an asterisk * next to the option.

Press the Save Option soft key.

Additional Tips

Because the TPM system shares its receiver with the remote locking system, the TPM function is turned off in vehicles that are built without the TPM system. It is possible to add TPM to one of these vehicles by adding the appropriate wheels and sensors. In this case, the TPM option must be enabled in the receiver.

TIP: If the horn does not chirp at the beginning of the reprogramming procedure (Magnet Method, above), this is a good indication that the TPM option has not been enabled.

Follow this path on your Tech 2:

Body

Remote Function Actuation

Special Functions

Set Options

Tire Pressure Warning

Read the instructions on the next screen, then press Continue.

Scroll to highlight the Tire Pressure Warning Option.

Press the Enter key to put and asterisk * next to the option.

Press the Save Option soft key

The system is now enabled.

If the car’s battery or the receiver is disconnected, or the voltage drops below a certain value, the receiver will lose all sensor Ids. It then sets all four DTCs. In this case, it must be reprogrammed using the magnet.

Sensor Batteries

On the Cadillac system only, the status of the sensor batteries is presented in the TPM data list. The sensors are built to continue to operate for three months after the batteries reach low status. When the battery in a sensor runs down, it is necessary to replace the sensor. Batteries are not serviceable.

[JasonA]

To be the devil's advocate, Consumer Reports tested consumer-grade tire pressure gauges back in 05/02 if you would like to reference the article online. They found six of the eight tested to be accurate within 1 psi across a wide range of pressures. The other two were accurate to within 2 psi.

I follow the notion that the TPM system is good for indicating flats. I wouldn't personally trust it like I would a real gauge. People come across that with the Chrysler systems on minivans too. They're just not accurate or reliable. One day reading high, the next low, etc.

And on my brother's Corvette, they're generally accurate, and generally match my tire gauge, but it can still vary up to a pound or two.

[Ranger]

On another note did you check the tires with the tire guage to confirm that the onboard was wrong?

Yes, when I adjusted each tire, I used my digital guage that is supposed to be acurate to 1%.

Another thing might be the air from the compressure you used may have been hotter/cooler more humid than the air you put in

I had plenty of air in the 60 ga. tank so the compressor did not run during the pressure adjustment.

TIP: The TPM sensor is more precise than consumer-grade tire pressure gauges.

Hmm, well this would blow the acuracy theory. As I said, I believe my guage to be of good quality, but who knows for sure.

Operation

The sensors operate only above 20 mph (32 kph) and transmit once per hour when parked, to preserve battery power.

I did not realize that they only worked above 20 MPH, but I am sure I was above that when I checked them. Since they transmit once per hr. when parked, the readings should be no less than an hr. old. I am going to go out and compare them again to the digital guage. The car has been parked all night so tires are cold.

Well, I guess I stand corrected. Tires are all at 68 deg. +/- 1 deg. Pressures with the Accurite guage read 30.5 psi on all 4 tires. TPI read 30 psi on all 4 tires. Brought them up to 32 psi on the tire guage without running the compressor so compessor air was probably about 68 as well. Guess I will put more faith in it from now on.

This is the guage I am using except mine does not have the flashlight in the handle (this is likely a newer version).

http://www.tirerack.com/accessories/airgauges/air7.jsp

[tjtjwdad]

Mine average within 1-2 psi of my tire pressure gage. Initially, I thought there was a issue but I was using a cheaper tire gage ad that was the culprit.

May not apply to your case, but I've heard that some places fill the tires with N2 and the hot/cold pressures don't fluctuiate as much.

Jim

[GreenMachine]

Mine average within 1-2 psi of my tire pressure gage. Initially, I thought there was a issue but I was using a cheaper tire gage ad that was the culprit.

May not apply to your case, but I've heard that some places fill the tires with N2 and the hot/cold pressures don't fluctuiate as much.

Jim

My local shop told me to stay away from the N2 fills because NONE of the tire companies are recommending it, plus most of the air we breath is filled with nitrogen anyway.

[epricedright]

Mine average within 1-2 psi of my tire pressure gage. Initially, I thought there was a issue but I was using a cheaper tire gage ad that was the culprit.

May not apply to your case, but I've heard that some places fill the tires with N2 and the hot/cold pressures don't fluctuiate as much.

Jim

My local shop told me to stay away from the N2 fills because NONE of the tire companies are recommending it, plus most of the air we breath is filled with nitrogen anyway.

I think they're passing along bad advice. I purchased my Michelin X radials from Costco and they use Nitrogen. I think the Nitrogen generating equipment is cost prohibitive for many tire shops, reason they will down play it's benefits. There's a reason all commercial aircraft, NASCAR, Indy, LeMans, Formula One, the U.S. Military, NASA, even Lance Armstrong and the Tour de France riders use it.

http://www.twafirestone.com/nitro.htm

http://www.autoblog.com/2006/05/03/high-ga...s-debate-again/

1. Michelin Tecnical Bulletin PM-03-05 "Michelin supports the use of nitrogen based on its ability to better retain air over a period of time."

2 Bridgestone Real Answers, Volume 8, Issue 3 "Nitrogen permeates through rubber more slowly. It might take six months to lose 2 psi with nitrogen, compared to a month with air."

3 from the same article "water vapor in compressed air acts as a catalyst, accelerating rust and corrision. Water vapor also absorbs and holds heat. And,when it changes from liquid to vapor, water expands tremendously in volume. So tires inflated with air tend to run hotter and fluctuate in pressure more.

4.Goodyear Product Service Bulletin PSB 2004-09

"Goodyear supports the use of nitrogen....., based on the ability to retain pressure for a longer period of time."

5.High quality Generators can produce 99.9% nitrogen, high quality installers quarantee 95%+ in the tire, as recommended by the "Rubber and Plastic News, Vol 34, No 4, pp14-19, 2004

6."Every day we are losing over 2 millions gallons of gaoline to a seemingly unimportant thing---low air pressure." US Department of Energy

Just documented facts--Bridgestone, Michelin and Goodyear do not sell Nitrogen Generating equipment.