Alphatero

I just had a heart stopping moment.
Driving along the highway at 85 and a loud beep goes off and the center display shows "Sudden loss of tire pressure"
I was waiting for the blowout to flip me over, but the car still felt stable so I slowed down and got off the next exit
I looked at the 4 tires and they looked OK, and then I manually checked each pressure and each showed over 40 (its hot out)
Its bad enough these low profile tires blow out with the least little thing, but I dont need this aggravation.
I cursed, reset the MMI tire pressure and drove on
The car is scheduled for service next week so I will add this to their to-do list
Has anyone had a false positive like this before?

superswiss

My initial guess is that the system wasn't properly reset before and you just perpetuated the issue by resetting it while the tires are hot. Only reset the system when the tires are cold and you've verified that the cold tire pressure is correct. Most Audis use what's called indirect TPMS. After resetting they need about 20 minutes of driving to learn all the necessary parameters. Only once the learning phase is done will the system work correctly and alert in a real situation. As soon as possible, reset the system when the tires are cold and you are sure the cold tire pressure is correct. One of the issues I have run into is that when the car is serviced, the tires are usually warm from having driven to the dealership. So they then check and adjust the tire pressure potentially before the tires had sufficient time to cool down and reset TPMS and now the system is not working optimally. Whenever I bring in my cars for service, I request they don't mess with the tire pressure. Here in CA it is mandatory for them to check and adjust tire pressure unless the customer opts out. I always check the tire pressure regularly myself and reset TPMS in case of the indirect systems. My current car has direct TPMS showing actual pressures and tire temperatures in the instrument cluster, and resetting TPMS stores the actual pressures as reference instead of parameters that feed a spectrum analysis algorithm that then determines if pressure is low. The indirect systems need to be meticulously reset whenever pressure is adjusted or wheels are changed or anything else in the wheel assembly is touched, otherwise they won't work correctly, and the reset must be done when the tires are cold.

BobaPanda

Yeah the TPMS system just looks at the RPM of each wheel and compares them with each other.

@Superswiss do you reset the TPMS that often? Even after I fill my tires up with air I don't reset the TPMS most times. I only reset it if it flags it, I check the tire pressure, and it looks okay.

superswiss

Yep, I check my tire pressures every two weeks and reset TPMS. As I said, my current car has direct TPMS, so now I don't reset TPMS anymore as long as I inflate the tires to the previously stored pressures. But with the indirect TPMS system there's much more than RPM that goes into them. The first systems only compared rational speeds, but these suffered from the obvious issue that if all 4 tires lose air at the same time there never was a difference in rotational speeds and they failed to detect the air loss. Today's systems are very sophisticated and actually measure oscillations through the ABS sensors that are directly related to tire pressure and digital signal processing algorithms evaluate these oscillations and can determine loss of pressure in one or more tires and can even pinpoint the exact tire(s) with air loss. Things like temperature changes etc. ultimately affect these algorithms so they only work properly if you rest the system and let it learn the new base parameters every time you make an adjustment.

Alphatero

superswiss - thank you for the detailed explanation of indirect TPMS.
But that doesnt address my question of why such a sudden false positive
The last time I set the TPMS in the MMI the tires were cold and I had just added air where necessary (several weeks ago)
So there is no "user error" here
Any other ideas?

davedavez

Yup, same heart-stopping thing happened to me about 6 months ago. Highway speeds, right rear tire sudden loss of pressure. No actual pressure loss. No fault codes either. Hasn't happened since, but certainly instills a certain amount of doubt in the system.

gguy

Sigh. Any TPMS system is subject to errors. Period. There are good and bad perspectives to all of the different styles. I have asked at four different tire stores now about the system that Audi uses. Every store tells me that the system that Audi uses is more simple and much more reliable. They all said to be very happy that Audi uses this system.

uberwgn

When the iTPMS is not correctly set up by the user, it will produce these errant warnings. The car must have the correct pressure threshold stored so it can do its monitoring.

superswiss

Not sure, but the only other thing I can think of is that they have a bug in the C8 or your particular one is malfunctioning. Audi's software quality has unfortunately somewhat gone into the crapper lately. Lots of issues in conjunction with the new touch MMI. The VW group as a whole is having real trouble with their software these days. They've all moved to the same underlying system, and all are showing similar issues, whether it's VW, Audi or even Porsche. Not saying that Mercedes and BMW are far better, they all struggle with this as it isn't one of their core competencies, but the VW Group seems to have a particularly rough time at the moment. Daimler just entered a partnership with Nvidia and they are planning to completely overhaul their tech by 2024. I'm curious of the results.

The iTPMS system as such that Audi uses has been in use since around 2010 and fundamentally works quite well. It's a third-party system that is well regarded. I've never had issues with it in my 2013 RS5. Some folks gripe over the fact that it doesn't show actual pressures in the instrument cluster and regularly question how well it works, but overall aside from perhaps some specific software bugs lately, it does the job and iTPMS saves customers from the expense of an additional set of sensors for winter wheels and having to replace them when the battery dies. Audi has started to offer direct TPMS in their performance models, first optionally and now it's standard on all RS models and the R8 as far as I know. Same for Mercedes-AMG and I believe BMW M. On these performance cars direct TPMS makes more sense, because they are also meant to be taken to the track and being able to keep an eye on the tire pressure and temperatures on the track is kinda important. But for normal daily driving, iTPMS is more than sufficient.

My guess is the dealership will send you away with we can't reproduce it and all they'll do is reset the system again, unless there is a known issue that Audi has a software update for or the car logged an error. Certainly worth bringing it up with your service advisor just in case there is a known malfunction.

doctorharrison

Happened to me twice in 13 months. Pulled over, inspected tire profiles and concluded, rightly so, it was an error message. My recommendation is to carry a tire gauge with you to ease your anxiety.