2002 Forester L
So, about 6 months ago my 9 year old Forester, with about 133,000 miles started throwing a CEL for the Cat., that would come on, go away, come back, go away, come back, etc. etc. I changed out both O-2 sensors, 4 spark plugs, and put on a new wire set. The pain continued. I had read about modifying the downstream sensor with with a spark plug non-fouler set on this very forum. I bought a set at the local Auto Zone for less than $5.00 with tax, printed out the instructions, modified the set as suggested on the link below, and installed it at my last oil change - at 140,000 miles. It took no more than 15-20 minutes. Hallelujah - 400-500 miles later and no CEL. It was a very simple procedure, except for a pretty tight fit between the exhaust pipe and floor panel. But it fit, with no touching or clanking and the f***ing CEL appears to be history. Three things to do, make sure you buy the 18mm set, there's more than one size, disconnect the battery and turn the lights and ignition on to drain the electrical system - this will eliminate the code memory, and unplug the sensor so you don't twist the harness while trying to reinstall it.