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Phrede 08-30-2010 11:05 AM

Hunting for battery drain
My '08 truck started having it's battery go dead after sitting for about a week. Nothing has changed electrically prior to this starting. I have some electrical mods, but nothing recent. I first disconnected the battery and let it sit, no problem. I then reconnected the battery leaving off anything I have added that goes to the battery, driving lights, power running board,etc, the problem was back.

After blowing the 2A fuse in my meter and ordering a new meter with a 10A capacity, I have found that there is about 600mA draw after waiting a bit from turning off the key. I pulled each fuse individually while watching the meter (under hood lamp is removed). A few of the fuses caused about a .003A difference but nothing major.

I really expected that I would have found a fuse that made a major difference, that would narrow the search, but none did. I disconnected the power distribution/fuse box and the meter dropped to 0.

Now I am left scratching my head. What circuit goes thru the fuse box but is not fused that could be pulling 1/2 amp with the key off? I am thinking normal draw would be .040 A or less. Agreed?

Ideas or suggestions?

Phrede 08-30-2010 12:06 PM


After letting the truck sit a little longer I measured the current drain at about 200mA with all of the fuses removed. F11 seems to have the largest effect causing some big differences when installed then settling down after a while.

I've discovered that the row of smaller connectors on the distribution/fuse block have the largest effect when unplugged. C1,C5,C6 and C7 combined account for around 50mA. Only after removing C2 and C4 together am I able to drop the remaining 150mA. I am now trying to track down these circuits and hope this is the problem.

Any advice is appreciated.

Phrede 08-30-2010 12:42 PM

Updated again:

I have learned the hard way that you must leave the ammeter in the circuit when waiting for things to stabilize (DUH!). Also, it takes pretty long, >15 minutes, for the truck to "go to sleep".

Right now with all connectors in and F11 only I have 650mA after 10 minutes.

Does anyone know why there are 2 different positions for F38? It has 3 socket holes and, of course, 2 pins on the fuse.

RamTech 08-30-2010 01:06 PM

That is for your power outlet. It allows it to come on with the ignition or remain on at all times. The CAN B system typically takes up to 20 minutes to go into sleep mode.

RamTech 08-30-2010 01:13 PM

Have you disconnected the underhood lamp? This could account for your draw on the F11 fuse.

Phrede 08-31-2010 10:29 PM

Fixed but still a mystery
Thanks Randy.

Took out all the fuses, disconnected all of the connectors on the fuse box. Measured, waited, measured, put it back together one step at a time, waited, measured.

In the end I have about 22mA of sleeping current, about what I would expect, and no clue what the problem was.

Sometimes things just happen.

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