Alternator/ Battery

[BigSilver]

2003, 6L, 2500 Chevy Suburban, 208,000km;

 

After lengthy driving, if I switch on the vehical's low beam lights, the engine goes into limp mode and a code p1518 becomes registered.

 

Replaced the battery twice so far in under a year.

 

Using a Shumacher 12000A charger, I checked the alternator condition, and it reports 100% effective.

 

Installed a freshly charged battery and drove for about an hour, and then rechecked the battery; the charger indicated only 65% capacity remaing in the battery; and yes, limp mode came on as soon as the low beams were powered up.

 

The voltage gauge on the dash never dipped below 14v. During a cold start, the voltage gauge displayed one mark above 14v, but as the engine warmed up the gauge droped to 14V.

 

Is the PCM controlling the charge cycle of the battery, or has the alternator had its life? (Read a few posts that the new alternator's outputs are controled by the PCM. If so is there a DIY work around, without the need for dealership involvement?)