Parasitic Draw

[kbuskill]

tested today, alternator is good (not drawing) and the draw is from the wire heading to under hood fuse box. I think I need to check the 3rd fuse box left to steering column.

can someone help identify what is the last wire (in attached pic) heading to?

thanks

View attachment 255055

I don't have a PPV but my guess would be that it leads to the starter just like all the other Non-PPV trucks.

 

[ramchol76]

I don't have a PPV but my guess would be that it leads to the starter just like all the other Non-PPV trucks.

thanks!

 

[RichardCranium]

If you run out of things to check on that power distribution block, I'd recommend doing how we handled parasitic draws on BMW's when I still was a tech. We had some models with 60+ modules, so parasitic draws were often as common as oil changes. FML.

Open the hood, trunk, all doors......manually trip the latches and detents so the vehicle things they are all closed. You should be able to verify this by interior and underhood lights going on. Allow the vehicle to sleep. For most BMW's in my days as a master tech (2001-2009), I was lucky in the fact that BMW used the gear selector indicator in the floor shifters as a light that also represented the sleep status of the car (when the indicator was out, the car was asleep). Not sure on GMT900's, maybe a GM tech or someone in the know on the forum can provide a visual indicator.

Once the truck is asleep, monitor the draw and start pulling fuses. Some are going to affect the draw, but you should be able to narrow down your culprit that way for sure. And 2.5A is pretty damn sizable, I don't know the specs of the GMT800 but I am sure its something like 20-40mA.

A lot of different modules causes issues with BMW's, but more often than not, especially on the lower models, the issue was the engine fans.

 

[bladenbullet]

it is not necessary to pull fuses and that can lead you on a wild goose chase if one circuit effects another (eg retained accessory power)...if you place a voltmeter across the terminals on the fuse it will read a very small voltage drop across the fuse if the circuit is active...this gives you an opportunity to keep the circuit alive while you look into it's operation or schematic...it will also give you an opportunity to see if multiple circuits are drawing without prematurely shutting them down...a removed fuse may stop a draw altogether if it is a module...then the whole process has to begin again to retest what is keeping the module alive (eg one of those switches you tripped that may have multiple contacts)

 

[Fless]

The internal diodes in the alternator are well known as sometimes going bad and causing a draw. Just unplug the alternator, when you see the draw on your DVOM, and if it goes away, the alternator should be replaced. Many other things can cause a draw but the alternator test is simple and fast. If unplugging the alternator does not stop the draw, then you start looking elsewhere and unplugging other items and pulling fuses till you find the culprit circuit.

When you say "unplug" the alternator, are you talking about the multi-wire connector, or the large DC cable?

 

[OR VietVet]

The multi wire connector.