Intermittent parasitic draw

[high mileage]

Guys, I have a draw that happens randomly. Sometimes if I leave the truck parked it'll drain the battery in 2-4 days, other times it'll be fine for a week or more.

New alternator and charge cable, replaced the agm battery twice. I've now done a full parasitic draw test and the only circuit that had mV was the info circuit, which only had 1.8mV.

Am I screwed? What's next here?

 

[Fless]

Confirm for us that the mV reading was across the fuse test points.

Depending on fuse size, has that reading been converted to A (or mA) using the appropriate Power Probe Fuse Voltage Drop chart? (Estimated draw varies by fuse size and amp rating.)

Resources – Power Probe

powerprobe.com

 

[high mileage]

Confirm for us that the mV reading was across the fuse test points.

Depending on fuse size, has that reading been converted to A (or mA) using the appropriate Power Probe Fuse Voltage Drop chart? (Estimated draw varies by fuse size and amp rating.)

Resources – Power Probe

powerprobe.com

Voltage drop across fuse test points. That way you never interrupt the ground on the battery. 1.8mV=.0018v

 

[Fless]

Voltage isn't current; that there is voltage drop indicates that there is current flowing in that circuit. But the voltage drop needs to be converted to current, so use the linked chart for the fuse type and size on that circuit and calculate the estimated current draw. We haven't been told the fuse type or its amp rating.

For example, if that's a 10A Mini Fuse with a voltage drop of 1.8 mV, there could be 1/4 A or so flowing:

To confirm the actual full draw when asleep, I would recommend connecting an ammeter inline in the negative cable where it connects to the battery. Then let everything fall asleep and see what the actual full system draw is. Maybe then pull the fuse in question to see if the draw drops accordingly. Monitor it for a while to see if anything is intermittently waking. Shoot for 25 mA or, ideally, less than that. 10 or 15 mA is a great number.

If there is anything aftermarket like an alarm system, radio, AFM disabler, etc., those are suspect. But you may need to look at wiring diagrams to see what's on that particular circuit.

 

[high mileage]

Voltage isn't current; that there is voltage drop indicates that there is current flowing in that circuit. But the voltage drop needs to be converted to current, so use the linked chart for the fuse type and size on that circuit and calculate the estimated current draw. We haven't been told the fuse type or its amp rating.

For example, if that's a 10A Mini Fuse with a voltage drop of 1.8 mV, there could be 1/4 A or so flowing:

View attachment 488848

To confirm the actual full draw when asleep, I would recommend connecting an ammeter inline in the negative cable where it connects to the battery. Then let everything fall asleep and see what the actual full system draw is. Maybe then pull the fuse in question to see if the draw drops accordingly. Monitor it for a while to see if anything is intermittently waking. Shoot for 25 mA or, ideally, less than that. 10 or 15 mA is a great number.

If there is anything aftermarket like an alarm system, radio, AFM disabler, etc., those are suspect. But you may need to look at wiring diagrams to see what's on that particular circuit.

It's a 10a mini fuse. The problem is I can't catch this idiotic draw, it happens randomly. I think what I'll do is to wait til it dies again then test with an inline ammeter while it's dead. It does have an afm disabler- should I disconnect that in the meantime?

 

[Fless]

Are you saying that the 1.8v drop on the INFO fuse isn't always there? I think I misunderstood from your initial post.

If it IS always there when the vehicle is asleep, that's enough draw to affect a battery. Maybe not overnight but within a day or two of sitting. I'd probably benchmark/document it by installing an ammeter now and seeing what the reading is. If it's consistent and repeatable, then while monitoring the ammeter I'd consider removing the AFM disabler to see how it affects the draw.

I don't see an "INFO" fuse in the online fusebox diagrams, unless I missed it -- where is it?

 

[mikez71]

I think INFO fuse is for the VCIM/onstar?

 

[Fless]

I still don't see it. If I'm looking at the correct diagram, F12 is the Onstar fuse: