Car died on side of road and wouldn't start. Looking for the problem.

Maybe it is time for a new ECM. Has anything happened to the car recently or any repairs been made in recent days? Not sure what ECM 672 means.

The used car dealer's mechanic says to try the upstream and downstream o2 sensors.....I tend to think it may be the ECM...Supposedly there was no history of this ever happening before this week according to the dealer. But we have only owned the car for a couple weeks and the dealer mechanic is the last mechanic to do any repairs to the vehicle

The CEL cat eff code was probably a PO420...if so ignore it for now. I too doubt that your ECM is screwed...UNLESS you bought a previously-flooded car, as the ECM sits under the passenger front rug (under glove box). You can pull up the rug from the front and you'll see a plastic shield, under which is the ECM andits harnesses. If they were under water I'd return the car under lemon law as a possible "salvage" status vehicle. State laws vary here.... O2 sensors have their own codes, so that's unlikely. Motor will not crank? Wrench check starter/solenoid operation? If ok car should crank. (If crank but no start check simple cam/crank front sensors as the ECM is "blind" to their function and won't throw a CEL.) I've to date not had to change a solenoid nor starter in any 2006- 2009 similar setup. The good news is that it ran ok for 50 miles, so again I'd look to the starter/solenoid operation, as "no crank" is rare if battery is strong. Need more info....

Just reread that car "died on road". While running?...or after you stopping it and simply trying to restart? The former would suggest it's NOT a starter/solenoid issue, and maybe something goofy like a fuel pump; the latter that it IS starter/solenoid related.

It is my son's car. it just died while driving..and there was quite a bit of moisture found underneath the passenger floormat and I did see that that is the location of the ECM harnesses...ANd since the car was used I didn't think it fell under the lemon laws...

If it's been in a flood zone it MAY have a salvage title. Did you check the received Title carefully. Again, different States offer consumers varying rights re used vehicle purchase. Under Mass law, for example, there would be both a general consumer protection as well a used car law protection. If you can't return this chariot that swam with the fishes at least remove and air-dry the ECM for several days and retry. Depending upon model some are easily uncased so that you can inspect the inner master pc board for wetness and/or residue...as well to speed drying. If no go, chase a pre-owned ECM, being carful to match, including 2-3 character code on outer case if possible, or you may lose an accessory function. Oh...just remembered: you must have your replacement ECM "coded" to your electronic ignition key or it won't start. Most mobile key services (as well Subaru dealer) will match your "new" ECM to existing keys quickly. Subies usually dry out successfully, but of course the ECM may need particular care. Check the top-of- transmission master harness connectors too. Even though they sit higher up, if the flood was severe they'll become oxidized and intermittent.

Thanks! I will definitely try drying the ECM and pursue a return / refund of the vehicle...