I had a tread separation near the sidewall on a tire so I had to buy one tire, I put it on the rear. Since my tires had 20K+ miles on them I knew the new tire would have a slightly different diameter. I haven't had any issues or codes but I'd like to know if slightly different diameter between the front wheels can cause any harm to the drive train. I would usually replace the whole set but these had plenty of usable tread left. Three appear to be 7/32s remaining with the newer tire at 8/32s. It's time to rotate this tire to the front. Thanks! I searched and found a thread that indicated it might cause problems: Interesting warning light -Video attached | PriusChat
1/32 I'd say you'd be OK. I understand Subaru (and some other brands) 4 wheel/all wheel drive vehicles are notorious for wanting the owner to change all four tires when one goes bad. My recollection is if the tires are within 3/32 you are OK to replace only one. Do an internet search to confirm as need be.
