During the post start (After starting) heater grid cycle, my volt meter stays at 12 for the duration, it does not cycle between 12 and 14 like I'm reading about other peoples trucks doing. After the 2-3 minute cycle the volts come up to 14, but shouldn't my volt meter be cycling as well? If so what could be wrong? What tells the heaters to cycle? JD

 

I believe if it is COLD outside then it will cycle. If it is NOT cold, it does not need to cycle.

 

I know that, what is my volt gauge supposed to be doing during the cycle?

 

It sometimes will cycle down from 14 to 12 but not always. It all depends on how cold.

 

If you would take the time to click on "User CP" up above and edit your signature, we would have an idea of what vehicle you are refering to. Thanks,

 

Thanx FMB...

 

Have you pulled any codes? (Engine stays off... Key to Run, Off, Run, Off, Run... read codes in Odometer... Will be letter P followed by 4 digits... says P-done when done". Post any codes.

 

I've got a 1650 code for bus comm. but I don't think it's related. I'm hearing that some of the trucks volt meter will cycle with the grid cycle and some won't. Not too sure what the rhyme or reason is. Wondering exactly what tells the grids to cycle. JDX

 

Once you start moving (over 25 MPH) the grid heaters no longer cycle. Are you moving?

 

No, after start up. During the 2-3 min. cycle.

 

Jet, mine will stay at 12v also until cycle is over. read some where that the ecm controls alternator charging, so to protect it from over current draw (grid heater draws about 200amps) ecm shuts down alternator. On others it may not or cycles it on and off. someone will correct me if wrong.