Engine/Transmission (1998.5 - 2002) Charging Issue

[jhoughton]

I have a 99 3500 that is only charging at 13. 7 volts. This problem only started a few months ago. So far I have checked the battery cables, Grid heater relay. I replaced the alternator with a 200 amp output with no differance. Looking for other ideas. Truck starts strong and fine always. Next idea was to check all the grounds. Others may have seen this before and have an answer. Thanks in advance.

 

[WestTN]

13. 7 volts would be about right for the temperatures we are experiencing in TN.

Battery chemistry is temperature dependent. In the winter months it will be around 13. 6 to 13. 8. Yoru are most likely right on the mark.

 

[B.G. Smith]

!3. 7 or 13. 8 volts is about the minimum charging rate. Probably wouldn't keep the batteries charged in short trip driving. The regulator is part iof the PCM and is not servicable seperately. It might be possible thart the batery sensor is causing the voltage to be low, it is located under the drivers side battery. You can check it to see if it is within specs, it has two leads, disconnect the leads and connect an ohm meter to the sensor leads, at 75-80 degrees F, the reading should be 9000 (9K) to 11000 (11K) ohms. If out of spec then that might be the problem. bg

 

[jhoughton]

I'll check the battery sensor. This was doing it on a trip to Washington where the temps were near freezing in the mountains coming back. Thanks for the thought.

Jim

 

[B.G. Smith]

If you are reading the gage on the dash, it is not very accurate. If you hook up a volt meter at one of the batteries at startup you should see a high voltage right after the engine starts then taper off to 13. 7 or so after the battery charges back up. bg

 

[WestTN]

The charging rate varies with temperature because it is a chemical reaction. 13. 7 @ 90 degF will recharge the batteys as fully as 14. 7 @ 32 degF. Chemical reactios are temperature dependent.

 

[Sticks]

Start your truck, turn the cab fan on high, all your lights (including the dome and cargo lights) hazzards, radio, and any other accessories. Hold the throttle at about 1500 RPM and see what the volts read with a meter hooked to either battery.

If you are still seeing 13+ you are fine.

 

[ichoplin]

Glad I found this thread. Just noticed my dash "indicator" reading straight up 14. I've had several CTD's and they have all read to the right of 14 volts. Been a little worrisome as I drive long distances at night. I checked my batts with a voltmeter while the motor was hot and running and it showed 13. 84 volts.
So can I relax and put my alternator rebuild kit in the toolbox? Btw, truck starts fine and everything seems normal.
Thanks,
Ian