OK. 2009 C6.5 A6 Avant, 3.0T, 142K miles. Just got new summer tires mounted, on the drive home I got an underinflation alarm. No biggie, checked the pressures, left front was 2-3 pounds lower than the other 3. Got them even, reset pressures in the MMI like always. But then, about 10 minutes into the drive, I get a "TPMS Malfunction" error? Checked the pressures, all good, reset pressures in MMI again, everything clears- then it does it again. And again.

Took it to my excellent indie shop (Dubwerx) and they hooked it to the VAG, read as an "intermittent different size wheel error"??? They cleared the ABS module and re-loaded the software- it seemed to fix it, but after 20 minutes of driving it came back on.

The car does NOT use TPMS sensors in the wheels, it uses the ABS system to monitor different rolling speeds. The ABS and traction control do not show errors and work fine. The shop is thinking a bad ABS module, but we are doing research first. Any thoughts or suggestions?

 

FIXED! Turns out it was a software issue and Dubwerx found a patch. Evidently the TPMS software (which uses rotational speed info from the ABS system) went "out of range" due to overall wear in the system- just enough that the software read a rotational issue but resetiing the pressure in the TPMS wouldn't hold, then eventually led to the "TPMS Malfunction" error message. The computer literally thought the wheels must be different sizes! Software patch installed, no problems since.

Dave