I have read all the threads about all the notorious codes, but I have a completely stock 04 wrx wagon. No catless downpipe, no catback, no intake. I have replaced the O2 sensor and p0139 still comes back. Now it only comes on every once in a while. But when it does, it will stay on for a day or more and then go dormant for a few days. I could just ignore it if it does no harm or doesn't rob power. Any thoughts?
hEY 04 REX,THERE IS A SUBARU REPROGRAM FOR P0139 DUE TO SPARK KNOCK,MAYBE YOU HAVE A FUEL QUALITY ISSUE OR TOO LOW A OCTANE...THE SPARK KNOCK MAY NOT BE HEARD BUT THE ECU IS CATCHING IT.I SUGGEST A REPROGRAM AND DOUBLE CK FOR ANY VACUUM LEAKS THAT COULD LET FRESH AIR IN AND SLOW THE RESPONSE OF THE REAR O2 FROM RICH TO LEAN OR VICE VERSA.GOOD LUCK!
So to do this, do I have to go get it tuned or is it a dealership issue? I run 92 octane all the time and use additives every once in a while. And a vacuum leak is possible. I noticed shortly after I bought the car I found a short piece of vacuum hose just sitting in the engine compartment, and on the end of it there was a (pistol) reducer. I didn't know what it was for but it wasn't connected to anything and it didn't seem to affect anything.