My Legacy died while driving (not a safe design) and displayed the Er HC code on the odometer. Had CAA tow to nearest Canadian Tire and they charged me $120 just to pull codes and told me they couldn't fix it and to take to Subaru dealership instead. Didn't really want to go to dealership (past bad experiences). So had CAA tow car to my house. Searched online for troubleshooting suggestions/tips. Finally came across a slow blow fuse (SBF #7) that was blown. Don't know why it was blown but replaced it and car came back to life! Pulled some codes P1714, P1718, P0700 and cleared them using the scan tool and so far so good.
But don't know what caused the SBF to blow - could have been the combination of dash cam and OBD reader constantly plugged in sucking too much power at startup? Didn't see any loose ground wires or anything.
