I have a malfunction in one of the "black boxes" inside my car as well (might be something like what Trigger posted about) that needs a rest on occasion to heal over itself.
Something to do with the main ECM and how it gives me an intermittent code for a non-functioning oxygen sensor, which is still shiny, after being replaced last year.
Disconnecting the battery for about twelve hours seems to fix it for a month or two.