All stock 2004 MM. No noticeable performance hit at all.
Got first light +/- 6 weeks ago. Codes were P0172 (lean indicator bank 2?) and P1235 (full pump driver circuit out of range). Reset, went a few days and came on again. Very trusted mechanic - Pikes Peak champ Clint Vahsholtz, total Ford guy - did full diagnoses with all the high tech gear. Nothing wrong. But just had fuel filter replaced with generic (along with thermostat and trans service with trans kit) a few weeks before.
He then consulted his own online sources and found these & similar codes sometimes triggered by non-Motorcraft filter. Pressure drop across filter just different enough. He replaced filter with Motorcraft, no charge, and Check Engine lights went away.
Until Monday, got one again. P1235. Showed reading of 8010 above normal max of 8000 (whatever those numbers mean...) Not really significant, Clint said.
Reset Check Engine light again; waiting for next time...
Any connection to this? Normally live and drive at 8500 feet. Every time, light only came on after driving down to Colorado Springs at 6000 feet.
Any suggestions would be much appreciated. Right now only solution seems to be to replace full pump assy. or fuel pump control module, or both. I don't want an important fault to be masked by this minor one. Not willing to drive around with Check Engine light on all the time.