TPMS sensitivity

[TheDr1ver]

First time post so hopefully this is the correct place (and that I’m not asking a question that’s been asked to death).

I have a 2016 A3 saloon. Pretty much since buying it last year, the TPMS will alarm every 250/300 miles. It’s always the passenger side rear tyre that it warns of. I always have my pressures to 35 at the front and 32 at the rear. If I check the pressures with my gauge the next morning, it’ll be something like 31.5 at the rear.

I don’t know how sensitive the alert should be. A 0.5 psi change seems a bit overkill, so is that the norm or could there be a fault with the system that I should get checked? Lately I just reset it in the MMI and ignore it until the next time it goes off.

 

[JohnM100]

Firstly, welcome.

The indirect TPMS on the 8V is not especially sensitive so I’d be surprised if 0.5 psi drop would set it off.

I have found it can occasionally be triggered by different road surfaces e.g. set it on tarmac and then drive on concrete for several miles (especially the concrete roads with scored channels to disperse rain).

As it’s the same wheel each time, suggest getting the wheel balance checked and swapping it with the wheel on the other side to see if the error moves with the wheel. At least that would rule out the cheaper fixes first before digging into the ABS sensors and unit.


You are in the 8L section but you car is an 8V.

Mods - can you move this to the 8V section?

 

[rafletcher]

As above, not very sensitive at all, especially with low profile tyres fitted. On 45 profile 18's I think mine alarmed at around 25, down from 32. Are you re-storing the "set pressure" after pumping up to the right pressures?

 

[eribaMotters]

There must be a considerable level of tolerance in the system. I thought it worked on the abs system sensors detecting a different peripheral wheel speed brought on by the tyre deflating and becoming smaller. I large rise or fall in temperature brought on by air temperature or just the friction between the tyre gripping the tarmac could esily result in the pressure changing by a few psi.

Colin

 

[rafletcher]

There must be a considerable level of tolerance in the system. I thought it worked on the abs system sensors detecting a different peripheral wheel speed brought on by the tyre deflating and becoming smaller. I large rise or fall in temperature brought on by air temperature or just the friction between the tyre gripping the tarmac could esily result in the pressure changing by a few psi.

Colin

TPMS that uses in-tyre sensors can be very sensitive to temperature change. When I briefly had a Toyota with such a system I was told by the salesman I WOULD see alarms in the winter due to low pressure from cold.

The Audi indirect system is just not very sensitive (yes, it uses ABS sensors to compare expected rotational speeds) but not unsafe.

You can of course buy aftermarket systems like this

Amazon product

if you want a real-time readout to compare with the "dumb" system's alarms.

With the above, beware the caps corroding onto the valve stems, use some decent grease and check regularly.

 

[S32B]

On the A3 I thought they only went off when a sudden loss of pressure occurred, not a slow loss?

I recall being in the middle of nowhere in NW Scotland when I hit a big pothole, a mile down the road the warning went off!!! at the time I had a basic foot pump. No phone signal, no people around, nothing! Heart in the mouth I stopped and checked, all was fine! Managed to drive 500 mile home, just stopping to check it every now and again. I put it down to the impact causing it the throw a wobbly. Since then I always have a compressor with me, which I've had to use a couple of times.

 

[TheDr1ver]

Are you re-storing the "set pressure" after pumping up to the right pressures?

Yes I am. I do it just to shut up the alarm every time I start the car as much as anything, but when I do get to a petrol station to top up the pressures, I reset.

My old A3 used to do the same thing. At least that one was an actual faulty valve - when it went off, the pressure had dropped from 32 to under 25. I'll might well take the advice from a previous post and swap the wheels to see if the alert "travels"