Boink

Seems I've developed a fairly slow tire leak (left front). It takes about a month for the system to detect a low pressure (as it drops from about 32psi to maybe the mid-20s or so). The car has only 10K miles on it. Valve? Wheel? Surely not the tire itself? It's definitely low when the warning comes on (i.e., not a false reading).
My dealer told me to bring it in if it happens again... and, sure enough, about a month later the system warns me again. I guess with this frequency, I don't mind filling it with the compressor in my garage. But why?
Thoughts?
Will a dealer charge for this service (in the first year)?

NABS4

Take it to a tire shop. They'll probably find a nail in the tire and you'll be charged $30 for the repair.

texasDFWS4

Discount Tires

superswiss

Huh? You probably have a nail or screw in the tire. This happens. Tires are wear items. Take it to a tire shop and if it can be repaired, it'll be plugged and patched and you are good to go. Depending on the shop you are looking at $30-$80 depending on whether you want the tire road force balanced after the repair. If it can't be repaired, you'll have to buy a new tire. Chances are the other tires still have enough tread left, so that you are within the tolerance of quattro and only need to replace one tire. Most tire shops nowadays offer road hazard programs, which reimburse for tire repairs and replacement tires, but the original tires are not under some kind of road hazard program unless you bought a tire and wheel protection package from the dealer.

chingwodapigu

Discount Tire will fix the flat for free, as long as it's not on the outer tread blocks because they will tell you it's too close to the sidewall to repair. If it's not repairable, then be ready for the sales pitch that all 4 tires will need to be repaired because quattro. If the tread depth difference is a large amount, but the remaining 3 tires still have lots of usable tread remaining, you can get the new tire shaved to have matching tread depth, but not all shops have a tread shaving machine. Tire Rack will shave the tread.
I recommend you have them check the tire for tread depth differential and see if they can find the nail/screw, without dismounting the tire from the wheel, because once they do that, they will not remount the tire if it can't be repaired, and that's how they force you to buy 4 new tires since they can't shave the tread, and they can't mount just a single new tire with a large tread differential.

Boink

Thanks all.
The tires are, essentially, like NEW (and came on the new Q5). I've had slow leaks before but never one that takes a good month like this. Seems like a VERY long time for a slow leak, which is why I wondered about the valve (since those usually show decline within a week).
Yeah, I suppose it could be a nail or screw that only allows a very small amount of air to escape (very slowly). There are a few local outfits that will likely repair it for free.

Probably un-related, but after 9 months, the tire-pressure warning light came on... and it turned out that all 4 tires had gotten down to about 22 lbs!!!

superswiss

Tires naturally lose air to some extent. The oxygen molecules escape through fine pores in the compound over time as the molecules are small enough. Pressure also changes as a function of temperature. Every 10F drop in temperature causes a 1 psi drop in the pressure, and a 10F increase in temperature increases the pressure by 1 psi. Now you definitely have a leak if only one tire is low and a screw or nail is the most likely cause, but not checking your tire pressure for 9 months and then be surprised that the TPMS goes off is solely on you. That's completely expected due to what I described above. Frankly, tire pressure should be checked and adjusted at least once a month. Every two weeks is even better. Set a reminder in your calendar. Regularly checking your tire pressure makes sure they are properly inflated and lets you adjust the pressure depending on the ambient temperature. Best done in the morning inside of the garage, before the sun or driving starts heating up the tires. Always check cold tire pressure.

Boink

UPDATE:
Just had the tire repaired.
Visited the dealer (while passing by) and they also thought it odd that it took so long to lose air in that tire. So, they inspected and FOUND A NAIL deep in a good tread channel. They joked that the nail had probably become part of the tire, thus the very slow leak.
The Audi dealer wanted $39.95 to repair with a patch (which seems reasonable)... but my wife and dog were in the car (and I couldn't wait then), so I had them top it off.
I then visited our local "Les Schwab" Tire Center (a northwest-based chain), and they patched it for free. Les Schwab is known for offering free patching as a bit of good publicity.
So, all's well!

Weebl

Running a tire down to the 20's multiple times doesn't do anything good for the sidewalls. Been there and done that many times and in the end it weakened it enough to get funky wear 10-20k later usually on the inside edges.
No, it isn't a toe/alignment issue.

Boink

Yep... I agree. Not good to run the tire down. Interestingly, I've now had a chance to see 32psi and 22psi, and I defy anyone to tell the difference (since there was no noticeable change in side-wall bulge)… with my 20 inch lower-profile tires (which probably have stiffer side-walls).