No you're not doing anything wrong Stanton500 has this problem seems to do with the year they don't seem to with the OBDII readers. I can't remember what the outcome was now. Not sure if it was the two black plugs with the forester that was done in the end. But I know it won't work like it does on anything around 2001 onwards the OBDII scanners.
I would say your diagnostic would be spot on, but check for pipes that might be split or lose :)