Changing a single tire will not change your alignment. It sounds like all the tires will be similar in tread depth so you should be fine. Thanks for the question!
Even in AWD there is usually a threshold of thread difference. I believe Subaru says there should be no less than 2/32nds difference between all tread depths. It all depends on the manufacture.
For example: If i bought 4 new tires and 4 months later a have to replace one of them I most likely can get away with doing just that one tire because there is no significant difference in tread depths.
Like DB stated you most likely have banded sensor being an early ford TPMS system. There are cheaper sensor tools that will simply trigger the sensor and make sure it is sending data.
Thanks for the question!
Thanks, db4690. That gives me a much better understanding of the system. I always like to diagnose up to a certain point before I enlist the services of a repair shop. At least I will have an idea if the system is working as it should with that tool, and then I can look at replacing the sensors, which, as others mentioned, certainly have marginal batteries by now.
Actually Subaru is very vague on tire matching. , only stating the following:
When you replacing or installing tire(s), all four tires must be the
same for following items.
(a) Size
(b) Circumference
© Speed symbol
(d) Load index
(e) Construction
(f) Manufacturer
(g) Brand (tread pattern)
(h) Degrees of wear
But obviously they are never identical. Even 4 new tires from the
manufacturer are not identical in circumference. There has to be some
tolerance. But Subaru is silent on this.
So I went to Tire Rack:
Here are recommendations from some of the manufactures that Tire Rack
currently serves for matching the tires used on their four-wheel drive
and all-wheel drive vehicles. Additional recommendations from other
Original Equipment Vehicle Manufacturers is (sic) pending.
Audi: As published in their vehicle owner’s manual, “rolling radius
of all 4 tires must remain the same” or within 4/32-inch of each other
in remaining tread depth.
Porsche: Cayenne within 30% of the other tire on the same axle’s
remaining treadwear. (!!!)
Subaru: Within 1/4-inch of tire circumference or about 2/32-inch of
each other in remaining tread depth.