jawildman

2008, 3500, 25K miles.

This weekend (which was the first one below 40deg since I bought the truck) I was driving at idle and the lights dimmed, glanced at the volt meter and it was around 10V. then it waved back and forth a few times and settled in just below 14V like normal. It did this a couple times, usually right after I started it. I did not have a separate volt meter with me. Each time, all the other electronics (fan, radio, etc) seemed to continue working fine.

I've checked the batteries for correct water, all the connections look very clean, though I have not pulled any of them. Hand held voltmeter shows 12.5V on the batteries with the engine off, 14+ with the engine on. Dash voltmeter is still very slow to come up to 12-14V. I rigged up a pig tail today and plugged in the handheld unit to the various power sockets in the cab. Voltage varied between 13.6V and 14.2V while driving. The dash meter never went over 14V.

Oh, and I had the local dealer change the oil on Friday (first occurrence was Saturday night).

My questions:
1) Hope this is the right forum, ie a 2008 is a gen 3?
2) At no time with the engine on have I seen the handheld unit below 13.6V. Shouldn't it always be above 14V with the engine on?
3) Is there anything the mechanic could have loosened to cause this (oh, you need a new pcm....)
4) How do I diagnose this?

I pull trailers with this truck and did short out the 30A fuse to the trailer a couple months ago.

CE Zero

jawildman;
I've been wondering the samething myself. I just thought it was the normal charge cycle after starting but it went away over the summer and is coming back with the cold weather, so now I'm thinking it might be related to the amount of time it takes to warm the Plugs and replacing that draw. Mine goes away after a couple minutes at the most. Mine will make a small click noise draw down the lights then click again a few seconds later and return to normal. Generally quits after 4 or 5 repetitions.
Dana

tryNto

There are no Plugs to heat up...
Our Trucks use a Grid Heater that heats the incoming air...
It cycles on & off as needed, Hence the Volt meter wavering and the lights dimming...
Completely normal....
Charging voltage, 13.5-14.6 is Fine...

jawildman

Thanks a bunch!!