Smart Junction Box ??
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Laughing Gas
Joined: May 2002
Posts: 875
Likes: 37
From: Ohio
Smart Junction Box ??
I thought I would start a new thread on this problem since I've made some progress. I have some parasitic draw that is killing my battery after about a week on not driving. Testing has isolated the problem to fuse 5 inside the right side kick panel. That fuse is for the keypad illumination, SJB microprocessor, and the brake-shift lock. I disconnected the shift lock and I don't has a entry keypad. Still getting a spike to .140 amps every so often. Googling SJB, the results basically say the fuse box is the SJB. I'm confused and wondering if I've gone as far as I can in diagnosing the draw. Am I missing something here? A 10amp fuse wouldn't control the while fuse panel. Is there a different part called smart junction box microprocessor? Ford-parts.com doesn't give me any clue either.
Thread Starter
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Laughing Gas
Joined: May 2002
Posts: 875
Likes: 37
From: Ohio
Thread Starter
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Laughing Gas
Joined: May 2002
Posts: 875
Likes: 37
From: Ohio
I had to reassemble everything that was setup for testing. The truck is not drivable with the fuse out, basically because of the brake/shift lock. All lighting is off, turn signals, TPMS, door locks, etc. From what I read online, the SJB controls many things and this seems to prove that info. I think I’ll check the connector in the rear tomorrow, which was mentioned as a possible area of corrosion.
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Laughing Gas
Joined: May 2002
Posts: 875
Likes: 37
From: Ohio
Probably too true in my case. What I read was that the fault in the connection would randomly short across the pins and cause a voltage surge. It seems that mine happens way too regular for that.
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Tuned
Joined: Apr 2015
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Likes: 68
From: N.E.Indiana
Is the duration of these spikes really short? How often does it do it( I know, loaded question) Are you ABSOLUTLEY CERTAIN that your battery is solid, 150 mils isn't a lot with all the electronics. Got me wondering if you have a week battery? Trying not to overlook the basics! Make sure your source is solid before you go chasing drain issues down stream. Jim
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Thread Starter
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Laughing Gas
Joined: May 2002
Posts: 875
Likes: 37
From: Ohio
Is the duration of these spikes really short? How often does it do it( I know, loaded question) Are you ABSOLUTLEY CERTAIN that your battery is solid, 150 mils isn't a lot with all the electronics. Got me wondering if you have a week battery? Trying not to overlook the basics! Make sure your source is solid before you go chasing drain issues down stream. Jim
And No, I don’t think the drain stays on for more than a few seconds, so I’m beginning to wonder if that’s really the problem.
Tuned
Joined: Apr 2015
Posts: 282
Likes: 68
From: N.E.Indiana
I feel your pain, how hard would it be to have that new battery tested? wouldn't be the first bad new battery. I reread both posts and I'm just not seeing your drain. rbentnail's suggestion on bms would be an easy test meanwhile. Keep feeding us info as you can, maybe we can help!
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Laughing Gas
Joined: May 2002
Posts: 875
Likes: 37
From: Ohio
I wish I had one to disconnect 🤔 From what I read, they didn’t start until 2011, one year after mine. I did disconnect something coming off the neg cable on the slight chance the truck had a BMS. Made no difference as far as the amperage spike.
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Laughing Gas
Joined: May 2002
Posts: 875
Likes: 37
From: Ohio
I feel your pain, how hard would it be to have that new battery tested? wouldn't be the first bad new battery. I reread both posts and I'm just not seeing your drain. rbentnail's suggestion on bms would be an easy test meanwhile. Keep feeding us info as you can, maybe we can help!
Tuned
Joined: Apr 2015
Posts: 282
Likes: 68
From: N.E.Indiana
As much as I hate to be a parts changer I agree with swapping sjb if you can find one. The thing that's tripping me up on the drain you're seeing is when you see 160 mils on your meter that's an hour not each second or each time you see it. Of course we can only go by what you've seen and we don't know what it's doing when you don't happen to be looking, that can make my thoughts on low drain way wrong. At any rate I think you're doing very well to be new at electrical trouble shooting
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Laughing Gas
Joined: May 2002
Posts: 875
Likes: 37
From: Ohio
The day was shot with Doc appt, watching my grandson and then mowing the grass. Tomorrow, I hope to be catching walleye all day long (sorry folks, gotta have some fun time once and a while). But I think I can get a SJB from Pull-a-part for around $20, providing it’s still in the Donor truck when I get there. If the battery tests OK, then that’s gonna be my next step. Hope it’s a good one! Does anyone know if I need one that would be a direct match up to my engine? Fortunately the one I’m looking at is, but if it’s not available and I’ll be looking for other matches!