2001 subaru outback h6 died while driving, no warning. Turns over good but won't start back. Computer says o2 sensor which has been on for 100000 miles. don't have locations od relays or sensors. Help

Hello, The Oxygen (o2) sensor will not cause a no start typically, because on cold start, the engine doesn't even pay attention to this sensor to create proper fuel and air mixtures. To find out what is going on, a proper diagnostic test must be performed to find out which one or ones of the following needed elements are at issue: 1) Fuel delivery 2) Ignition spark 3) Air coming into the intake -- either restricted or too much 4) Exhaust flow restricted Is there a check engine warning light illuminated? If so, testing can start there to find out what trouble codes might be present, aiding with clues as to where to start looking for your problem. If not, each system I listed must be tested to see if it is working properly. A well trained technician with a good diagnostic tool that has data monitoring capabilities and a shop manual to use for reference will be able to get to the bottom of your concern with little difficulty.