Electric phantom

[CNCwell]

My battery keeps draining. I had the battery and alternator tested and both are good. The truck starts right up with a jump pack and runs fine while I'm driving. After it has ran for 20 minutes or so the battery has enough charge to start the TB for about an hour, after that it dies again. I have checked to ensure that all the light switches are off and cant find any bare wires making contact and causing a drain. Do you guys have any ideas for further trouble shooting?

[navigator]

I did some research on this a few months back for a senior at our church. He had a similar issue in his mini-van. Below is what I can remember reading when researching his van. Most of it will apply to most any platform.



There are a couple of ways to check for a parasitic drain. Do some searches to get familiar. I would have to search to refresh my memory. If you(or a previous owner) have made any upgrades that might be the first place to start looking. Think about if you have any electrical upgrades (lights, amps, aftermarket alarm, remote start etc) or is everything stock?

One way is to check your fuses while the truck is off to see what has power, one might be obvious.

The best way I have read (and again my memory is foggy) has to do with disconnecting one of the battery cables (I can''t remember which, likely the negative) and connecting your volt meter in between the battery and the cable. I think in a lot of newer cars when you disconnect the cable and then jump it with your meter there is an initial draw you have to wait out the system resets, buses etc. If I recall that is about 10 minutes. After that initial draw your meter should show how much draw you have while off. You can then start pulling fuses and see which ones cause the meter to drop and by how much. The one that causes the largest drop is likely the culprit.

To verify you can pull that fuse (after a full charge) and see if your battery dies again.

[navigator]

If you find a good write up on checking for the parasitic drain, post the steps here to help the next guy out and make sure to let us know when you find it.

[CNCwell]

If you find a good write up on checking for the parasitic drain, post the steps here to help the next guy out and make sure to let us know when you find it.

Thanks for the info, I will begin researching now. I'll let you guys know what I find.

[The Roadie]

I've written this up a few times on the other sites. In general, disconnecting the battery cable resets all the modules and you will never find one that failed in the usual way that when it's running, it fails to go to sleep when it should.

I have a clamp-on DC ammeter which is rare and expensive, but is only one of two ways to measure milliamps in a power feed without disconnecting it to install a series ammeter. The other is to separately hook up the series ammeter from the battery terminal to the load while the load is connected the usual way, then disconnect the usual way. This is easier if your battery has independent top terminals.

Some modules stay awake for a while, and some intermittently wake up like OnStar so they can listen for remote unlock commands. And some small draw is normal, like under 20mA, that runs the remote keyfob receiver circuit in the LGM.

But in general, be HIGHLY suspicious of any aftermarket entertainment material, remote starts, and head unit adapters to retain chimes and steering wheel controls.

Look for inadvertently turned on lights, like the vanity mirror or glovebox or underhood lights if you have the rare 2002 that have those lilghts.

Pull the OnStar module - high failure rate.

Pull DDM and PDM connectors.

Otherwise, you can pull fuses one at a time after you stop and see if the issue goes away, then trace that circuit and see what it feeds. That way can take days, however.