2009 Audi S5: Waking Up to a Low Tire
October 29, 2009
What a way to start the day. Yesterday morning I was greeted by a low tire warning a minute or so after I left my driveway in the 2009 Audi S5. But that's not to say the tire went low somewhere in those first couple hundred yards--it doubtlessly dipped below the trigger point while the car sat overnight.
The delay comes from the way most TPMS systems operate. The in-wheel pressure sensors and their transmitters are battery powered, but the need for long battery life means they don't broadcast continuously. Update intervals range from once per minute to once every three minutes, and reports are not necessarily issued at engine start.
And that's why I got a half-mile or so down the road before the warning came on.
I drove directly to my neighborhood gas station, where the normal-looking left front proved to be at 28 psi instead of the 39 psi that's specified for an S5 front tire. I topped if off and drove on to the office without further incident.
The reason for this pre-dawn delay was a leaking plug/patch installed last month after Brent picked up a large hunk of debris.
According to our trusty local tire store, the guy who installed this plug went a little overboard and bored too large a hole, causing our slow leak and making it impossible to re-repair. So we've had to install a new matching Dunlop 255/35ZR19 tire at a cost of $330. Total damage with tax, tire disposal fee, mounting and balancing came to $396.18.
The good news is this: TPMS saved the day again. We've had more than a half-dozen experiences like this, in which leaking tires that never actually looked low never had a chance to develop into roadside flats.
My gripes? The S5's TPMS minimal system does not have position intelligence or a direct pressure readout, so I had to check all four tires with my own gauge to find the low tire. On top of that, the system requires a manual system reset through the MMI screen after you reset your pressure (and the trigger threshold) to whatever accuracy your handheld gauge possesses. Most cars do this automatically.
Dan Edmunds, Director of Vehicle Testing @ 10,985 miles