I've had my '03 HO 3500 for 6 years (bought at 110k; now has 158k), and it always bothered me that my voltmeter shows about 13v before and after engine start, and takes about 2 minutes before the voltage jumps up to about 14.8v on the gauge?

It's done it since I bought the truck, so I guess (?) it's normal, but I'd like to know why.

It does it if it's the first start of the day, or when the engine is warm.

I actually measured the battery voltage yesterday after start, but before the instrument panel meter rose, and it was showing 14.4 volts (instr panel meter showing about 13v), so I gather the alternator is charging right away after the engine is running, so why does the panel meter take so long to respond?

I have a diesel tech who owns an '04 and he said his does the same thing (says it's controlled by the PCM) so I shouldn't worry about it (I was thinking maybe it was time for a new alternator), but I am curious...

Normal? If normal, what's it doing/why?

 

This time of year the lower voltage is probably due to the grid heater drawing power. Mine sometimes cycles so I can see the meter go up after running a minute and then back down before the engine heats up.

 

I disconnected the grid heater fusible link so it they cannot draw any current and it STILL acts the same.

On the other board, other folks say theirs does it the same because the gauge is PCM powered and programmed to act that way.

They said the Gen 2 trucks would vary like you said, but the 3rd gen just lies for 2 minutes or so every start.

Go figure!

 

I think that is pretty normal. The gauges seem to be driven by the ECM, which might be why it responds slowly. I believe the computer also regulates/controls alternator output.

 

Its normal. I kinda think the computer doesn't even start the charge process until after several seconds of run time and if the grids are on its delayed until they stop cycling. Its got to be a tremendous electrical load in the winter at night with a start and then grids and headlights and full blower motor running defrost or what ever.




47