perdido34

I have a 2010 A4 quattro (no sport package) with about 18K miles. As I was driving to work on the freeway last week, the TPMS warning message went on, telling me to check all four tires. I parked the car a few miles later and looked at the tires--none of them looked exceptionally low. When I took the car to a Firestone tire shop at the end of the day, the tech said that all four tires were below 20 lb (normal is 33 front, 35 rear). He guessed that all four wheels had rim leaks, which he said were common on aluminum wheels. He pumped up the tires and had me bring the car back the next morning.

AFter work, he told me that he tested all four tires in a water bath. There were no rim leaks or nail holes. So the tires didn't need to be dismounted. He pumped them up to the normal pressures and I reset the TPMS.

I then called the local Audi dealer. The service tech said that if the tires were all below 20 pounds, they would have looked flat (they didn't) and there would have been sidewall damage (there is none). He said to bring in the car. A day or two later, the TPMS signaled a problem with the right front tire. I stopped the car immediately and checked the pressure--35 pounds. I reset the TPMS and drove to the dealer. The tech now told me that this was probably due to the drop in outdoor temperature in the last few days. Two days later, the TPMS again signaled to check the right front tire--which is still normal.

OK, so what's going on? My first thought was that the tire dealer lied and falsely claimed the pressures were way low so that he could charge me $80 to remove corrosion and repair rim leaks. But he didn't find any and he didn't charge me for that. I wondered if his tire gauge was wrong--but how likely is the gauge at a tire shop to be off by over 10 lb??

So what could be wrong here? The dealer said that the TPMS goes off when pressures drop by a couple of pounds, which could happen when the weather gets suddenly colder. But this has never happpened over the preceding year, with plenty of sudden changes in temp. The only time the TPMS went off before this week was when I had a flat.

perdido34

Possible solution to the mystery: Yesterday afternoon, the TPMS signaled that the right front tire was low. Looked fine to me, so I parked it. This morning, with the tires cooled after sitting all night, the TPMS signaled that all tires were underinflated. I immediately checked all front tires with two completely different gauges. The right front tire was low (25 lb), but the other three had been overinflated by the tire store by about 10 psi. So clearly their tire gauge IS way off. When they told me the tires were all below 20 psi, most likely they were all below 30.

My plan of action is never to return to that tire store! (and also to keep an eye on the right front tire, which is the only one that I actually measured as low.

Vito Roma

Could def be due to weather changes or could be something else. If the tire does look flat with any leak more likely than not it was the weather change from night to day or vice versa

perdido34

I thought about that. The first time the warning came to check all 4 tires, the temp had indeed dropped about 20 degrees F overnight. But the light didn't come on until I had been driving for 20 minutes, including 10 minutes at 70 mph. By that time, the tires would have warmed up enough to compensate for the loss of a few psi, which the dealer says is enough to trigger the TPMS system.

When the weather went UP overnight from the 40s to 61 degrees which happened yesterday, and the TPMS light then told me that all of the tires were low when it had signaled on the previous evening that only one was low, that could not be explained by a drop in temperature!

gunsmoker

Yours is a 2010 which doesn't have a direct TPMS so I'm surprised it can tell you that all of your tires are low. My understanding of how this works is that it memorizes the ratio of the average number of turns between the wheels for a certain distance and that's why on cars with an indirect TPMS you have to drive them for a while right after you set the pressure and reset the TPMS. If you have different pressures on the fronts vs. the backs it will come up with different numbers and all it will be monitoring is those ratios as the enviroment temperature and the tire temperatures go up and down.
I suppose for close tire pressures it can assume that the pressure depends on the temperature in a linear fashion and if it has memorized that the front ratio is 1:1, the back is 1:1 and the front to back ratio is 1.1:1, when it sees ratios like 1:0.8 (front), 1:1(back), and 1:1(frint-back) respectively, it will set the alarm.

This is not a very precise system, but chances are you have a tire that is losing air.
My wife's car had a flat tire recently and her car has a direct TPMS. She called me and asked me what to do. I told her to drive to the nearest tireshop if she ccouldn't tell which tire is flat, otherwise to call AAA. She went to some indie shop and they told her that the pressure on one of the tires was 2psi below the others and that was probably due to the weather and sent her out. I told her that that's BS because I set the tires with a digital gauge with a .5psi resolution. The tire was down 12psi the next morning. I put the spare on, showed her the nail in the tread and sent her back to the shop. They supposedly fixed the tire for $4.20 and the tech said he removed a piece of metal. I told her that was BS - plugging a tire costs $10-20 around here and I don't think they have discounts for beautuful babes. The tire was flat the next morning. I sent her to another shop where they fixed it for $20.

Then I had to set the pressure to my liking and retorque the nuts. I always do that after any tire shop. The luxury dealerships are OK on the torque, but the indies can easily damage your brake rotors with uneven torque. I had to jump on the wrench to undo the nuts. One nut slipped and I had to buy a new one.

perdido34

Perhaps, but the tire shop that I went to at first said they put each of my wheels (with tires on) into a water bath and found no sign of rim leaks, or of leaks from the tread. Although it appears that their tire gauge may be way off, which makes me doubt their work, I have to believe they would have been motivated to find leaks (or even falsely claim they found leaks) in order to have me pay up to correct the leak(s) or to sell me a tire or two.

But I will continue to check the most likely suspect, the right front, because it was in the 25 psi range today, while the other tires (all four had been inflated by that tire shop) had over 43 psi.

4Rook

They may have overinflated to test for leaks in a water bath and forgot to air down afterwards. It's becoming harder and harder to find good service. Like you said, just keep monitoring the cold tire pressure and be sure to note the ambient air temp as you take your readings.

audi8k

I also wonder about the alarm for all four wheels, but in addition to monitor the rotation ratios, the description of the system says it also monitors the vibration characteristics.
Have you felt any vibrations?

Another possibility would be a system fault. Perhaps reading out failure codes can give a hint.

perdido34

I haven't noticed any vibration at any speed. When I did take the car to the dealer, the tech didn't even look at the car, let along the failure codes. He said, "We get 15-20 people a week coming in here about the TPMS at this time of the year, when the temperature drops. The pressure goes down a couple of pounds because of the colder weather." Which doesn't apply to my situation, because the TPMS has gone off with a 4-wheel alert when the temperature has RISEN 20 degrees over the previous day.

ghag_S4racing

I'm wondering if the batteries that are in the TPMS' have a low charge and like all batteries when they get cold they loose some of their charge therefore giving these false readings. Looking at the information provided on this link below.


http://www.tpmssource.com/?gclid=COP...FYmK4Aodiye_xQ