Wow! That's crazy high! It will tell you which tyre if it's sure, but it's not always able to be 100% in which case it gives the generic warning.

"Only" 50 PSI :eek::confused:

Hmm, I'm glad others had better luck. I had a flat tire and it never came on. My tire, back passenger, went flat overnight. I drove a block and something didn't feel right and pulled over. TPMS never alerted me.

TPMS needs to be calibrated by setting the proper pressure in the tires and then setting the system through the MMI. Perhaps the TPMS on your car was never calibrated.

I had a tyre blow out the other night due to hitting a pot hole. Instant heavy steering but I drove another few hundred yards to find a safe place to pull up. TPMS didn't say anything, but it was calibrated recently as I topped the pressures up and did it in the MMI in the last few weeks.
And yet in the past it has triggered on the slightest loss of pressure of only 4-5 PSI.
So maybe it's a bit hit and miss...

I had a similar experience about a month ago. TPMS said rear left tire pressure was low. Pumped it up at the station and then brought the car in to the dealer the next day. They didn't find any puncture, just that all tires are very low (20-25 psi). So this one seems to be cold weather related--that and my lack of diligence in routinely checking my tires.

However, what makes me less than reassured, is that this "indirect" TPMS does not appear to trigger that easily especially when all tires are losing pressure at similar rates. I would like it to warn me way before those mid-20's psi numbers are reached.

I wonder if it is possible to switch to a "direct" system by purchasing and installing four new in-tire sensors. Does anybody know if my 2013 Q5 is equipped with the necessary hardware to communicate with them?

Audis equipped with the passive TPMS system do not have the electronics to read the PSI transmitters so installing them would not work.

When I had the direct sensors in my '09 A4 (the last year for most Audis), they didn't seem to register an alert any faster than the indirect TPMS I have currently. It took about a 7-9 lb PSI drop to get a warning.

I got to test mine yesterday, The warning came on and said "low rear passenger tire". Ran to a tire shop and it was down by 7 psi and had a nail in it.

This is a very good point. I think the TPMS depends on an individual tire rotating at a different rate than the other tires; indicating a different circumference; thereby inferring a pressure problem. But, as you point out, if all of the tires are equally low, it may very well not detect a problem. I'll bet that you are correct about this issue. Agree, not re-assuring.

Needs 8 psi loss to activate warning.....
 

as stated by Audi.

Just some info for owners wondering why their tire may be 4-5 psi low and no warning.