P0251

[BigDiesel]

Truck set the voltage idiot light today. Plugged my code reader in and pulled a P0251? Everything I've read about this is either the optical sensor circuit or a faulty pmd or ip. Funny thing is my truck hasn't skipped a beat. It's running better than ever, no power loss, excessive black smoke, or any other issues. Optical sensor guru's???

[DmaxMaverick]

Check/clean the grounds and all the battery terminals.

[DaveBr]

http://www.thedieselpageforums.com/tdpforum/images/icons/icon1.gif
If you are using an additive in your fuel it could be the problem. I had this happen to me. I changed to a different additive and that was the end of the problem. If this is not the problem and the grounds don't help then it's time for a new I.P.

[BigDiesel]

Didn't set a code today, but my voltage goes from 12 up to 14.5 sporatically. The voltage light stays on till my truck hits 2400rpm and that's also the point where my tach starts working again. Truck runs great, no misfires, hesitation, nothing.
The ip is only about 2 yrs old with maybe 45000km on it and I use stanadyne perf formula almost every tank.
Could it be the voltage regulator in my alternator?
Checked my cables. Connections good. Battery's are only 6-7 weeks old.

[DmaxMaverick]

It's the alternator. Your battery idiot light, varying voltage, and sporadic tach are the pointers. Either find a wire harness issue, or replace the alternator.