According to the Forester’s manual, the Tire Pressure Monitoring System kicks in after the car reaches 25 mph. It evidently takes a while to figure things out after that, because the TPMS light blinked on a mile from home on the way to Mary’s Vassar Farms garden. I pulled into the next parking lot, measured 20 psi in the left rear tire, then found this staring me in the eye:
Well, that certainly simplified the diagnosis!
I unloaded two bags of shredded leaves and a pile of hoses, swapped in the (limited use, donut-style) spare tire, and continued the mission.
The TPMS light wasn’t on when I drove to Squidwrench the previous evening. Judging from the wear, that screw appeared during the various errands following our 800 mile road trip, which is good news of a sort, and depressurized the tire over the course of a day or two.
The receipt from the fix-it folks cautions that a plug is a temporary fix, because “the injury has compromised the integrity of the tire”. On the other paw, the Forester manual tells me “All four tires must be the same in terms of manufacturer, brand (tread pattern), construction, and size. You are advised to replace the tires with new ones that are identical to those fitted as standard equipment” and then provides a checklist:
When you replacing or installing tire(s), all four tires must be the same for following items.
(c) Speed symbol
(d) Load index
(g) Brand (tread pattern)
(h) Degrees of wear
There’s absolutely no way to get an identical replacement tire, let alone one with the same tread wear, but I am so unready to replace all four tires after 12 k miles / 2 years.
We shall see how this works out…