I have a 2003 5.9L diesel 3500 When its below 60 degrees outside and truck is cold (has been sitting for more than 4 hours)....The alternator will not charge at idle...or anything below 2000 rpms for that matter. Once i put the truck in drive and start driving, i have to get the rpms up before it hits second gear....then the alternator activates and starts charging. If i just let it sit there and idle....the alternator will start charging after maybee 5 minutes or so. Untill then, it just sits there and the lights dim every time the intake grid heaters cycle on and off while its cold. This issue just started this year.

 

That's all perfectly normal. The grid heater cycling will cause the lights to dim/get bright until the ECM sees certain conditions. I know it monitors intake air temp, coolant temp, and vehicle speed. Does the transmission shift fine after it has gone "through the gears" once? The ECM will not allow the transmission to shift "normally" until the trans fluid reaches a certain temp. (I can't remember the exact temp off the top of my head) When was the last time you changed fluid/filters and adjusted your bands?

 

yes it shifts good gage my dad has a 2005 and his doesn't do it. was trying to find out why the alternator wasn't charging when the truck was started why does it wait for a while to start charging?

 

We have a voltage gauge and not an amp-meter gauge in our trucks. I'm not sure why you think the alternator is not working? The gauge doesn't tell you if the alternator is working or not.

 

Have you had a load test done on your batteries?