When in idle my Battery meter seems to go up to 18V then drops down to 14V then back up again. This does it every time i start my truck, Checked batteries with volt meter and they both are putting out 12.55 v when truck is not running. Any idea's?????


Chad...

 

Grid heater cycling?

 

How do i check to see if it is cycling?? Dumb question sorry

 

That does not tell you anything. If you want to check the condition of your batteries you have to check them under load. Which in most cases means pulling them out of the truck and taking them to Cambodian Tire or Napa etc.

What kind of voltage do you have with the truck running? IIRC, should be at least 14.4 volts.

Do you have any codes?

Your are not familiar with the grid heaters? When its cold the grid heaters will cycle and draw 90+ amps to heat the air entering the combustion chamber. This causes the voltage to swing wildly as the grid heaters turn on and off. The grids stop cycling until the truck is warmed up sufficiently or until it reaches 18 mph (I think).

 

Multimeter on the connections of the grid heater.

 

If he is spiking up to 18V, then there is a voltage regulator problem. Neither of my trucks has ever gone over 14.4V, and thats in the real cold weather. Days like today, it is around 13.7 and hot summer days its around 13.2V. The dash gauges are a very rough estimate. Fire up the truck and use a multitester to check the voltage as it swings. Hopefully its not up at 18V.

 

oh, I didnt catch the part about the 18V..

 

Ok ill try doing this after work, right now super buzy trying to get my Rig and equipment rigged out and on the road. The period 1 road bans go on Monday from Hwy 16 south, break up is here. Boooooooo!!!

 

No codes, voltage is 14.81 on both batteries. for some reason it didnt swing when i tried it, ill try again tomorrow.

 

The voltage is regulated from your PCM. The older trucks use a volt regulator module. I wonder if something is up with the alternator field coil. Thats the part the engages the alternator to charge and not to charge.