aeromark

Had a flat tire recently and the system never alerted me. I tested the system yesterday by checking/setting/storing tire pressures and then dropped the pressure by 10 psi in in two tires - no alerts.

Has anyone else seen this?

DennisMitchell

I think you have to drive a distance before you will get the alert. It won't happen in driveway.

MurrayA4

Yes this Audi Tpms system works by comparing rotational speed of the wheels/tires using the Abs sensors.When you "store" values in the MMI it then monitors rotational speed for a certain distance and that becomes the baseline.So yes it only works when your vehicle is rolling.It's simple and works well.I've had mine alert twice on as little as 3 psi pressure loss.

aeromark

The original flat - I drove several mile with little to no air and damaged the tire. After the two tests I drove a couple of miles each time. Not much sense in having this system if it does not alert in a mile or two. Our Sienna TPMS alerts even with a few pound differential just after we leave the garage.

MP4.2+6.0

Having owned both the Sienna and now the Q5, they both alert roughly the same. Apples to apples, w/ Sienna we switched out from the sub par run flats fairly early on. I have had nails and such in each vehicle and they do alert by the time you can visually see the tire is low on air. They are fundamentally differential read systems looking for rotational speed differences among the wheels, so in general one tire has to be lower than the others to the point it affects rotational speed. Not sure if it will pick up all the tires being low at once (there may be an outer parameter calculation too), or if two on the same axle read low at same time. A differential read system (without actual in wheel pressure sensors) may also not pick up a sudden blow out in the short time from moment you feel it to stopping. As in, if I were testing it, I would lower pressure on only one wheel and then drive for a while. Up at 32 or 35 psi tire flex is going to be minimal, so testing probably needs to be down in the low to mid 20's to have enough rotational difference. Mine has certainly alerted to differences like that, which is when you can start to see it in the sidewall if you are familiar with how a low tire looks visually.

aeromark

Thanks for the suggestion(s). I lowered the pressure in one of the rear wheels to 18 PSI and drove 5 miles.........nothing. I also ran the diagnostics on my Carista. No errors (other than the side assist for which its going in for service on Friday). I'm going to have the dealer look at this as well - this is a safety issue if its not working and there are no codes or warnings.

shokhead

That's odd. What is set in your mmi?

aeromark

MP4.2+6.0

Yep, doesn't sound right. I specifically had a nail in rear left and it alerted a couple of different times as I tracked down--I pumped up in interim just to get by (wife's car) and then get to tire shop to patch.

Redd

Aero-
I tend to almost agree with Audi's logic on this one. By using the revolution-counting in the ABS system, they can make the TPMS system all software, so there is essentially no production cost to build it. Also no extra unsprung weight in the wheel, no parts, no o-rings leaking, no batteries always wanting to be changed requiring tires to be unmounted and remounted. It makes good sense to do it this way.
Except, as you note, this logic seems faulty, it certainly is not as sensitive as "real" TPMS systems with tire sensors. Many of them also do not go off until one tire is +10 pounds down, some will go off at 3# down. Coming from "always lived without it" into the world of TPMS, I have to say I'm not entirely impressed with TPMS. It winds up adding costs and complications and as you've found, it sometimes seems grossly oversold.