Tyre Underinflated Warning On

[Passatier3]

Driving to the the office this morning a message flashed up to say that a tyre was underinflated and that the data would be saved to MMI.

I checked the screen to see if it gave me the pressures and which tyre but it was greyed out.

The orange tyre symbol has also come on.

I pulled over to check the tyres and all seems fine and again after being at work for a few hours - gave them all a thump with my hand and they all seem OK. Will check them with the tyre gauge when I get home.

I did increase the pressures on Sunday as the car was going to be loaded up but did 300 miles and no alerts. Are you supposed to set something if you alter the pressures?

[Wuffles]

Yes, it wants to be told you have changed them so it can monitor the new pressure...or so I have figured out anyway. Had that message a few times, once when I switched the fronts for the rears and once after it had been in the dealers.

[johnsimcox]

As the TPMS in the C7 is based on using the ABS sensor to check a significant variation in the rolling circumference of the tyre, every time you change the tyre pressures you need to reset the system via the MMI screen so it knows that this is the correct tyre pressure/circumference. This also allows it to make adjustments for tyre wear.

[Passatier3]

Thanks Wuffles - Unless you can remember I'll consult the handbook this evening to see how to reset it.

Funnily enough, whilst doing a search, came across a thread by the Passat lads who have a choice between part and full loads and if the pressures aren't as set by VW then they get a warning - how daft is that!

And thanks John, posted at the same time.

Just wondering why it took so long to flash up a warning? Over 300 miles! :D

[Wuffles]

It's easy enough to reset the pressures in the MMI. In car systems probably. It doesn't tell you what they are either, just "set them to this" kind of thing.

[Passatier3]

Cheers, I'll have a play. You mean to say that Passats (Sport) have individual tyre pressure readouts and our Audis don't! Oh, the shame of it! :D

[johnsimcox]

Thanks Wuffles - Unless you can remember I'll consult the handbook this evening to see how to reset it.

Funnily enough, whilst doing a search, came across a thread by the Passat lads who have a choice between part and full loads and if the pressures aren't as set by VW then they get a warning - how daft is that!

And thanks John, posted at the same time.

Just wondering why it took so long to flash up a warning? Over 300 miles! :D
You need to do Car>Systems>Servicing & Checks>TPM>Store TP>Yes, Store Now

The manual seems to suggest that the system alerts to low pressure not over inflation so you may still have an issue, worth checking. If it is just one tyre then it should also indicate which one.

[Wuffles]

First time I had it was when the wheel had been off at the dealers to do something with the brakes, as far as I know they didn't switch tyres around, so it didn't make much sense. It also didn't come on until after 30 miles or so from leaving the dealers and getting home.

[Passatier3]

Thanks chaps, that was quick and easy. Was greyed out when I was driving.

Yes, I will check again when I get home to be on the safe side. I need to drop the pressures back down a bit anyway. Not that it makes much difference with those tyres! :D

[Kieron Mullan]

A word of caution, DO NOT rely on the TPM to advise when your pressures are low (over time). I had the system on my A5 and if the pressures slowly drop over time (broadly equal across the tyres) you can find your pressures down by as much as 10psi and still not get a warning. The ABS system is really designed for punctures.

There's no substitute for a manual check each week etc anyway.

Cheers

[Passatier3]

Absolutely right Kieron - same system on my wife's Mini and as you say pressures can drop over time and there is no alert.

Finding that post about Passat's having real time pressure monitoring has miffed me a bit! As would be nice to have a look at the pressures now and again. That's the trouble I guess with cheaper cars getting better and better specs. because the more expensive (like the A6), but not top of the range cars (A8, Q7 etc.) have the quandary of needing to be perceived as better/more upmarket cars but at the same time can't be seen to be competing with more expensive models with regards to toys, if that makes sense?

I know a couple of guys with Ford Focus' which are better specced. than my A6. I know which I'd rather have though! :D

Designers must be really struggling with what to put into more upmarket cars now to differentiate them from basic family cars.

[skibuddy]

You need to do Car>Systems>Servicing & Checks>TPM>Store TP>Yes, Store Now

So what is being stored? If the loss of pressure is detected by the ABS system in someway, how is tyre pressure measured and stored when the vehicle is stationary? What does a stationary vehicle have to do with relative wheel rotation and ABS? Is the wording in the MMI simply a hangover from previous model where the pressure was actually measured and store by pressure gauges in the tyres?

[Wuffles]

It's just an annoyance for me.

If I have a blow out, on non-run flat tyres (which I presume these are) then I'll know about it. I won't be waiting for something to tell me there may or may not be a drop in pressure when I've seen it make stuff up in the past :confused:

[Kieron Mullan]

So what is being stored? If the loss of pressure is detected by the ABS system in someway, how is tyre pressure measured and stored when the vehicle is stationary? What does a stationary vehicle have to do with relative wheel rotation and ABS? Is the wording in the MMI simply a hangover from previous model where the pressure was actually measured and store by pressure gauges in the tyres?

ABS or indirect TPMS primarily uses the ABS system to measure the rotational differences between each wheel/tyre combination in conjunction with differential sensors and a specialised software programme. When you press 'store' in the MMI, in effect all you are doing is resetting the system, so the programme can relearn the rotational differences over the next 20-40 mins of driving and as long as they are within the software parameters, the system accepts the revised calculations.

The significant shortcoming is if you have slow puncture and top the pressure when you get home and leave the car overnight without driving it, you could be asking the system to recalibrate based on 'what is now' a potentially lower pressure than when you pressed 'store'. And, as long as the rotational difference is within the software parameters, it will accept the now 'incorrect' pressure, leaving you to drive round wearing out your tyre due to under inflation until the parameters are exceeded. A manual check is the best way to keep on top of it, and only use the TPMS as notification of a puncture or flat tyre. By the way, different tyre types (due to tyre wall stiffness /manufacturing methods) and spirited driving over a bumpy road can also set the system off.


It's just an annoyance for me.

If I have a blow out, on non-run flat tyres (which I presume these are) then I'll know about it. I won't be waiting for something to tell me there may or may not be a drop in pressure when I've seen it make stuff up in the past :confused:

AFAIK, Audi does not fit run flats as OEM, these are only fitted as an aftermarket purchase - why anyone would though is beyond me, unless you want a really stiff ride.

Cheers

[royclark]

AFAIK, Audi does not fit run flats as OEM, these are only fitted as an aftermarket purchase - why anyone would though is beyond me, unless you want a really stiff ride.

Cheers

Can you fit runflats to standard alloys ?

[jbanfie]

We've had the ABS based rotational difference system on the wife's Mini's for the past 3 years and our experience is that it is really good and caught a couple of slow punctures that we had fixed for £10 each rather than waiting for the tyre to get ruined by running on a flat tyre.

The dealer set the tyre pressures on the A7 10 months ago and I've not touched them since (other than checking the pressures from time to time) they are good as gold!

[Wuffles]

Had them on an E46 BMW convertible - which didn't require a service for the roof every few miles either - and the ride was just as hard as you'd expect from a thin walled tyre, but not overly. The run flat element only kicked in if the tyre blew, you're not constantly running on the hard bit afaik.

[johnsimcox]

It's just an annoyance for me.

If I have a blow out, on non-run flat tyres (which I presume these are) then I'll know about it. I won't be waiting for something to tell me there may or may not be a drop in pressure when I've seen it make stuff up in the past :confused:
Don't blame Audi it is an EU directive (Latest News - European legislation on TPMS imminent (http://www.techeurope.co.uk/tech/news/view/35/European-legislation-on-TPMS-imminent)) that all newly launched cars from November last year and all new cars from November next year must have a TPMS as standard. Most manufacturers have adopted the VAG approach of measuring rotational variation via the ABS system as it is much cheaper and maintenance free compared to the systems that require special valves etc (imagine the hassle at your local Kwik-Fit when they do not have the right replacement valves for your specific car)

[johnsimcox]

Can you fit runflats to standard alloys ?
AFAIK runflats require special alloys that are designed to work with the larger beading on the tyre to keep the flat tyre on the rim

[Wuffles]

I recall the tyres also had a very handy anti kerbing protruding rubber ring which I am positive my Wife would love to have on this car too - I'll pop out and ask the front alloys in a minute, I'm sure they'll agree.

Didn't have any issues getting tyres fitted by a local indy place, just had to make sure they were ordered in for next day - they were very low profile and not the sort of thing Kwik Fit would have stocked anyway I wouldn't have thought.