manjack

I have a 2005 F-150 with the "petite" (4.6 liter) V-8. A couple of weeks ago the check engine light came on, and the code reader didn't register anything. That's when I learned that the diagnostic circuit and the cigarette lighter are on the same fuse -- which was blown. I replace the fuse, got the code reader to power up, but it came up with no codes (ran through 01 to 05 with nothing) and then said "ERR." The reader couldn't reset the light.

I disconnected the battery for five minutes and the light went out, but now it keeps coming back on, this time without the fuse blowing. Same thing: no codes, and the light won't clear with the reader (have to disconnect the battery). Once reset like that, it will light up again after 15 to 30 minutes of driving (doesn't seem to matter how many startups).

Any ideas are appreciated.