4WD + Headlights = Loss of Power???

I just came home from work for lunch and since over the last 24 hours we received about a foot of snow I was in 4WD. I was not in 4 because of the snow, but rather for traction as I pull onto the highway from the side road my office is on.

Anyway, I have about 1/2 mile drive to the highway and am going about 30 mph (speed limit is only 25). It's still blowing and snowing up here so while driving along I turned on my headlights. As soon as I turned the headlight knob, the whole truck shuddered and lost power. What the heck?? It scared me for a brief moment it was such a violent shudder and the loss of power was so severe I thought the truck actually stalled.

The truck didn't stall, but it didn't quite run the same either. There are no lights on the dash (I had an issue with the Jill descent feature during the run) and everything appears normal.

Anyone else ever have this happen or have any ideas what the heck happened?

I tried to turn off the off road mode while driving above speed. A fail safe must be in these trucks so some thing with that might be messing up. With mine I just drove to the farm shop and shut it off and waited a min and it started back up with no issue. With computers some times they need to be rebooted I'm sure the trucks are the same.

First ive heard of this.. the battery could has a bad cell or the alt took a big draw, maybe the belt got wet and slipped.. is it still doing this now?

I'm thinking you where in limp mode is why it didn't seem to run the same with shutting it off and restarting should reset it's self. I would recommend doing that at a safe location if all gages look ok.

I agree sounds like battery issue.. "slow speed" (not driving highway speed) cold, seat heaters, short trips at lower speed.. Low battery state and during on headlight dropped voltage just enough to cause computer to trip out..

-Greg (aka squatting dog)

I'm home for lunch now and I didn't pull into the garage in the off chance it doesn't restart and I need a tow. A restart "fixed" my Jill descent issue during the run so I'm hoping all will be fine when I start it in a few... Very strange. Like I said, it was such a severe shudder I think I jumped as much as the truck did.

I thought I destroyed my truck when I shut off the off road mode it was violent. that is what makes me think yours went into limp mode. fingers crossed for ya.

Ms. MI Raptor said:

I'm home for lunch now and I didn't pull into the garage in the off chance it doesn't restart and I need a tow. A restart "fixed" my Jill descent issue during the run so I'm hoping all will be fine when I start it in a few... Very strange. Like I said, it was such a severe shudder I think I jumped as much as the truck did.

Click to expand...

Got to load test the battery and check what the alt output is... Unless its still under warranty... then you know what to do... lol

Well, just drove back to work and repeated exactly what I did on the way home but nothing happened. I guess that's good and bad. The truck's a 2012 with 20,000 miles so I'd much rather it break now under warranty than later... But at least I have the extended warranty so a couple years for this to happen again.

My old boss has a 2010 BMW M3. He usually took very short trips and was having issues similar to yours. BMW told him the alternator does not put out enough wattage at idle and low speeds to serve all the functions of the vehicle, and at these low speed the battery draw is increased to compensate.

There is a clutch in the alternator that varies the output, and for some reason, maybe they can only go so low.

Perhaps your battery was low due to cold temps, heavy draw and what not, like Pooping Dog said, and the head lights drew enough last power that it freaked the ECU out.

I would say drive faster and watch for it happening again.