Key Off Draw

This will be quick, just wanted to share the latest key off battery draw complaint I had.

Once I was hooked up I could see there was nearly 5 amps of current!
Anything pulling that kind of load should have been obvious, but no lights were on, no motors or pumps were running, so the first test I did was disconnect the B+ cable from the new alternator:



And after about 30 minutes it fell down to about 20ma.

Good find. Did you busy happen to check it after you installed the alternator or did something happen that led you to test it?

Sent from my moto g fast using Tapatalk

I did not install that alternator, it came in like that.
Just a semi educated guess, plus it was easy to get at

I’m curious if you have a theory as to what it took so long. It seems to me that as soon as you unhooked the B+ the voltage would have stopped back-feeding and the draw would have gone away?

AJeep18 wrote: I’m curious if you have a theory as to what it took so long. It seems to me that as soon as you unhooked the B+ the voltage would have stopped back-feeding and the draw would have gone away?

That does seem a bit weird. Looks like it only dropped to ~1/2 amp when the B+ wire was disconnected. And control wiring appears to have already been unplugged so the alternator couldn't keep anything awake thru' it??

Does the vehicle have a battery current sensor? A 5A reading from it might keep some things awake??

It dropped 4.3 amps with the battery feed disconnected, down to 450ma.
Which did seem awful high to me, but I wasn't ready to go digging around the fuse box just yet since I knew the modules all would still be awake because I just started the draw test.
So I went after a crank no start Yukon in the parking lot while I waited for everything to time out.

And you are correct, I disconnected the control harness to ensure it was just the alternator that was the source of the draw and not some weird fault in the control circuit.

Every time I looked back at it (every 10 minutes-ish?) it stepped down consumption more than 10ma. Eventually on one of my passes by the car it had fallen to 20ma.

Oh I see, I didn't look at the picture close enough. :blush:

Nice one !
I had that a few years back -- didn't have much in the way of diagnostic equipment at the time so it took me a bit of scratching around. It was an even bigger drain it was a Lucas Magneti Marelli so pulled 3 blade multi plug at the alternator --- big fat spark ! problem found
Now if I see a big current drain I go straight amp clamp the alternator and wiper motor first.

Must be one of those new cold start aids that keeps the engine bay warm !

Good find.

Yeah, I'm sure the critters under the hood didn't mind cozying up around that thing at night.