Hey
I thought my tyres had a slow leak or were not sealed right, but they are all fine.
I know it will go down over time but I am not sure how long or how much pressure needs to go before the sensor kicks in.
I put 35psi in all around 16" , this was about 3 weeks ago and the sensors went off again.
Is this normal? My last car did not have the sensors so I am not sure how often these go off and usually how much pressure is lost over a few weeks and when to be worried?
Thanks all
I don't think you have "sensors" at all. Audi have usually used an "indirect" TPMS system that relies on the ABS sensors, and not a "direct" system that uses in-tyre TPMS sensors. (this applied to my '14 A4 and my '18S3). This IMO is a good thing, due to the expense of sensors, the complications if you have winter and summer wheel sets, and the fact the foam repair kits kill not only the tyre but the sensors.
So, assuming yours is indirect - you pump up the tyres and set the "pressure" in the MMI - the system works by comparing rotational speeds for the wheels using the ABS sensors. If one wheel starts to rotate at a different rate (due to change in circumference due to loss of pressure) then the warning will come on. IME it took a decent drop in pressure - more that 10 psi on the 18" 45 profiles on the A4 - to get it to show up - and with 35 profile tyres even more so!
I'd suggest that you may have a slow leak (not necessarily a puncture - mine was cured by getting the garage to pop the tyre and use some tyre sealant on the rim) that is showing up. Could be valve, could be a corroded rim, could be poor refurb paint lifting at the bead..
If you're particularly concerned get an aftermarket TPMS system - for some reason the forum is stripping out the hyperlink I posted - search for Jansite TPMS on Amazon
These use sensors on the valve caps - but beware - there are LOTS of stories of the caps corroding to the valve stems and being impossible to remove, thereby necessitating a new valve. A decent grease on the threads and a monthly check avoids this.
As side note. I (briefly) had a Toyota Corolla with direct TPMS. I was warned that on frosty mornings the alarm WOULD go off (assuming I'd pumped up the tyres at a relatively warm temp) due to the drop in pressure caused by the cold - so they're very sensitive.
ETA - generally the warning has never gone off in my Audis, unless I've had a puncture or a leak. I check my tyres about once a quarter!