Tyre Pressure Monitor

[oake]

Driving home from the coast last Saturday night, a message came up to the effect that one or more tyres had lost pressure. Of course, the message came up when I was nowhere near anywhere with a filling station, but I diverted into a town and found a car park. Visual inspection didn't show any obvious problem, and I eventually found a small filling station with an air/water machine. According to the label on the driver's door, the recommended pressures are 32 psi front and 29 psi rear, and petrol station air lines are not designed to provide any useful information, so I simply set the machine to 32 for the fronts, and 29 for the rears. It was fairly dark, and there was traffic noise, but I didn't detect any inflation happening - in fact, I think the machine let a small amount of air out of the rears. (Yes, I know pressures should be checked cold, but I was simply trying to ensure the thing was in a drivable state.)

Having done that, I set the MMI to say the pressures were now correct, and continued my journey.

So is this something that happens with MMI - does it detect just a tiny difference in pressure, and raise an alert? I'd always thought the feature utilised the ABS sensors to detect a change in the effective diameter of the wheel, but I'd have expected the pressure drop to be quite significant to trigger that, and I don't think that applies here.

I guess I'll just have to wait and see - if it happens again, it might mean I have a slow puncture. However, if that were the case, I thought the MMI could indicate which tyre was affected.

All advice gratefully received!

 

 

[oake]

Further to the above, I'm now struggling to understand what my tyre pressures should be. The manual refers me to the plate on the driver's door, photo attached:

My tyres are 225/45 R17, and there are three sets of pressures on the plate for that tyre size. I assume the left hand symbols represent number of passengers, so I would need 35 psi front and back if the back seats were regularly occupied. However, my back seats are 99% unused, so I need to apply one of the other two sets - but which one?

The second group seems to suggest I should look in the manual, judging by the little "book" symbol, but the manual simply refers me back to the plate on the door.

If the figures were broadly similar, I'd toss a coin and take my chances, but they're quite significantly different.

I'd be grateful for any advice.

 

[WPAWS]

see what this sight gives you mate

https://www.tyresafe.org/check-your-pressures/

[niedzial1983]

The sensor is built in in the valve in each wheel , there is aslo a reciver above the wheel arch that picks up the signal. And yes the system will alert about any drop in pressure as this is saftey device 

[oake]

4 hours ago, Paul A6 said:

see what this sight gives you mate

https://www.tyresafe.org/check-your-pressures/

Thanks Paul. I got an answer from Audi on the interpretation of the figures on the door plate.

The bottom set, with four symbols on the left, are for fully loaded, with four passengers, as I suspected.

The first set, 35 psi front and 32 psi rear, are their standard recommendation for normal driving.

The second set, 30 psi front and 28 psi rear, are recommended for a comfortable ride.

The site you linked to suggests about 32 psi front and 29 psi rear, which are within Audi's range, and I think I'll use those.

Thanks again.

[oake]

5 hours ago, niedzial1983 said:

The sensor is built in in the valve in each wheel , there is aslo a reciver above the wheel arch that picks up the signal. And yes the system will alert about any drop in pressure as this is saftey device 

Thanks Piotr, but I'm not sure my system is as sophisticated as the one on your A6.

All I got was a generic message telling me that there had been a loss of tyre pressure - no indication of which tyre was affected - and I'm sure the system you describe could provide a more specific message.

Also, I found no evidence that any individual tyre contained less pressure than its partner on the same axle, which is why I was trying to establish what the pressures should have been, in case the system was expecting higher pressures generally for some reason.

I'll just have to monitor it and see what happens.