Tyre pressure warning system

[Hammer2001]

Drove the car this morning for the first time in a few days.
Noticed a rough rumbling when I pulled away and stopped to find a completely flat passenger side rear tyre.
Thankfully a puncture that was repairable so didn't have to pay out for a new tyre.

The car gave no warning on the Tyre pressure warning monitoring system.

Before when I've had a puncture (and I've had 3 in 2 years with this car compared to one in 20 years with my previous cars!)
the system has issued a warning whilst driving.
Anyone know how it works? Does it only issue a warning if there is a large pressure drop and therefore would not warn for a slow puncture that happens when the car is off?

will teach me to visually check all 4 tyres before I get in in future!

[M1tchy]

If you go onto the "car" menu, then servicing on the right hand side there is an option to set the tyre pressures. once you have inflated them and they are all correct you need to tell the system that they are right so they can then monitor any differences in pressure.

[Hammer2001]

Yes M1tchy, I do that whenever I top up my tyre pressures.

It's just there was no warning. Considering the tyre was completely flat I would have expected it to flag a warning immediately when I started the car.

[mr.ots]

The tyre pressure monitor will only indicate a puncture when the car is moving as it monitors the rolling resistance at each wheel. A tyre with less pressure will create a higher rolling resistance when in motion. There is no monitoring of the actual pressure within the tyre.

[Hammer2001]

Thanks mr.ots.
I probably did not get above 20 while driving down the road, due to the rumbling sound. I decided to stop and check before I went any quicker.
So maybe the system will only detect over a certain speed?

[wildbore]

The tyre pressure monitor will only indicate a puncture when the car is moving as it monitors the rolling resistance at each wheel. A tyre with less pressure will create a higher rolling resistance when in motion. There is no monitoring of the actual pressure within the tyre.

I think that the system is measuring the rolling circumference of the wheels via the ABS speed ring sensors. An under-inflated tyre has a smaller rolling circumference.

[richlean]

I think it also needs to drive a certain distance to be sure of its numbers, and avoid false alarms. I forgot to reset it after changing to winter tyres, and drove for a few minutes before the warning came on. I suppose it's designed around slow punctures.

[ukgroucho]

Yes it uses the ABS sensors as I understand it. I think they went away from the monitor embedded in each wheel because of the additional complexity and also because they were very prone to being destroyed by over-enthusiastic tyre changing folks.

I have had mine go off twice... once for all 4 wheels indicating they were under pressure. I put this down t having collected the car early July when the temp were up around 30C so Audi will have set the pressures and 'calibrated' the system at that ambient temp. In late Sept / Oct we had a cool spell and I think that was enough to drop the pressures 2 or 3 PSI so it went off for all 4 wheels - but I'd driven maybe 4 miles.

Second one was a slow puncture from a nail... too close to the side wall to save the nearly new tyre of course.

[fest0r]

Using nitrogen should help with pressure fluctuations.

[ukgroucho]

Using nitrogen should help with pressure fluctuations.

I've tried it but it makes me dizzy

[mr.ots]

I think that the system is measuring the rolling circumference of the wheels via the ABS speed ring sensors. An under-inflated tyre has a smaller rolling circumference.
It is the abs sensors that are doing the measuring.

[folkwagen]

Is it possible to add tpms to an A6 C6 2007, some kind of software upgrade only. It would be useful. I had the esp light come on several times on the very morning of my National Car Tes, same as DOE in UK. It would go after a stop/restart and a few hundred yards. I was hoping it would stay off during the test. Just before the test I checked tyre pressures, and found one with only 18psi and a slow puncture. Pumped up and esp light has stayed off. This got me thinking, it would be handy if this could be programmed to alert soft tyres.

[johnsimcox]

Is it possible to add tpms to an A6 C6 2007, some kind of software upgrade only. It would be useful. I had the esp light come on several times on the very morning of my National Car Tes, same as DOE in UK. It would go after a stop/restart and a few hundred yards. I was hoping it would stay off during the test. Just before the test I checked tyre pressures, and found one with only 18psi and a slow puncture. Pumped up and esp light has stayed off. This got me thinking, it would be handy if this could be programmed to alert soft tyres.
Suspect not. On the C6 Audi offered the more advanced Tyre Pressure Monitoring system with sensors in the wheels. With the EU mandating that cars should have Tyre Pressure Loss sensing they adopted the cheaper ABS sensor solution. Doubt the C6 has the necessary functionality in the ABS and MMI system to allow it to be activated

[Tripletrouble]

I managed to hit a lump of metal on the M1 yesterday. I thought I had got away with it but 5 minutes later the low pressure warning chimed in.
I pulled over and sure enough the tyre was "soft" and slowly deflating. Just my luck it was a new tyre which I had to have replaced today as the sidewall had a minute hole in it.
The lump in question was one of those handles truck drivers use to tension curtain siders with, it made a hell of a bang when it hit the underside of the car!

[ukgroucho]

Ugh sorry to hear that... been there with my allroad with a nail near the edge so no repairable - and with quattro you run into this issue of not wanting the tyres to be too different in tread cos it winds up the diffs so generally you rotate front and rear to get similar wear and then do a complete change of a set - throwing a replacement tyre in midway causes confusion.

You said it delivered a bit of a bang to the underside... you might want to get that checked in case it damaged the 'skirt' (underbody pan) or other stuff like the exhaust system.

[Borab0y]

Thats the problem with the indirect system, you need to drive it a while before it realises you have a problem.

Regulation 64, which covers the TPMS laws in europe, says it has to inform the driver within 10 minutes which means you could be driving on a flat for up to 10 mins before the system tells you.

The direct systems generally have a box in each wheel arch that forces the sensor within the tyre to transmit it's data when you either key on or as soon as you start moving and therefore informing you straight away, although, in the ever increasing need to cost save, the box in the arches are being removed and the TPMS ecu needs to receive data from a moving sensor before it will display the low pressure lamp, which usually takes about a minute of driving above 15kph.

[chesterfield]

Using nitrogen should help with pressure fluctuations.
I tend to fill mine with 78% nitrogen.

[jbn]

I tend to fill mine with 78% nitrogen.

...which can be had for free at most garages (gas stations) :banghead:

Ironically I was reading this thread over the weekend, and today shortly after setting off, a couple of minutes after I had felt something was a little odd the alert came on advising that my front passenger tyre was low; which indeed it was. Depending on exactly where I picked up the offending nail I had driven either a couple of kilometres or only about 600 metres. Either way, it works but the question is bit like Schrödinger's Cat: had I not read the thread would I then still have needed the alert this morning!

[fest0r]

...which can be had for free at most garages (gas stations) :banghead:

I think chesterfield was just making a little joke ;)

Just for clarity, using pure nitrogen to fill your tyres will lower the percentage of oxygen to roughly 5% depending on pressure.

It’s open to debate, but nitrogen is a non-reactive gas (unlike oxygen) so in theory fluctuates less during heat/cold cycles. It also lowers the chance of moisture in the air line which definitely does cause fluctuations.

The other supposed benefits such as being less corrosive and not losing pressure as quickly are also contested, but at the very minimum it’s not any worse than bog standard compressed air.

[johnsimcox]

I think chesterfield was just making a little joke ;)

Just for clarity, using pure nitrogen to fill your tyres will lower the percentage of oxygen to roughly 5% depending on pressure.

It’s open to debate, but nitrogen is a non-reactive gas (unlike oxygen) so in theory fluctuates less during heat/cold cycles. It also lowers the chance of moisture in the air line which definitely does cause fluctuations.

The other supposed benefits such as being less corrosive and not losing pressure as quickly are also contested, but at the very minimum it’s not any worse than bog standard compressed air.
...also Nitrogen molecules are larger and therefore less able to get though the gaps between the molecules in the tyre wall meaning that pressures will not drop over time. That said in reality for the vast majority of us it will make precious little difference

[jbn]

Yeah... I remember the composition of air from science classes in school ;) but actually it does make a small difference as you (fest0r) and johnsimcox note. I'm a physicist not a chemist - Schrödinger's Cat was just my little joke.....

[AudiNow]

With the tyre warning system should you be able to see the BAR that each individual tyre pressure is at?With my RS6 I was able to but it seems with my BITDI I cant, it just lets me store the new tyre pressures but doesnt show me which each individual tyre pressure is currently at

[jbn]

As noted further up this thread and elsewhere, the system uses the output waveform from the ABS sensors to detect that something is wrong with the rotation of the wheel => tyre pressure. This is why it also takes time to alert and only when moving. Reseting the system does not store the current pressures, it resets the waveform recorded so that the next output is recorded as the basis for comparison. You can over or underinflate your tyres as much as you like, reset them, and then the car will make no comment until there is a substantive change in the pressure of at least one tyre from that baseline.

[johnsimcox]

With the tyre warning system should you be able to see the BAR that each individual tyre pressure is at?With my RS6 I was able to but it seems with my BITDI I cant, it just lets me store the new tyre pressures but doesnt show me which each individual tyre pressure is currently at

RS6 may be different (not had the pleasure of driving one) but as far as I know all C7s have the ABS Sensor based system whilst the C6 had the more expensive tyre valve sensor as an option.


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[vwcabriolet1971]

There are 2 distinct types of VAG tyre pressure monitoring systems . The cheaper type works off the ABS sensors and sensors underinflated tyres by sensing that one wheel is turning more quickly than the others due to the smaller rolling radius. This type is normaly called a "flat tyre indicator " as it does not sense tyre pressure directly. The other more expensive tyre valve type has individual pressure sensors at each wheel. Some more upmarket models show these tyre pressures on a dashboard display ( for all 4 tyres). This type was an expensive option.