Powertrain Malfunction / Reduced Power: Fix #34

[chl]

Agreed with everything except grounding, I'd think the system remain grounded even without the battery. As far as the edit about the DCDC not able to handle spikes, it may be true, but I don't think its very likely since there really isn't that much 12v draw in the truck without accessories and it's not very spiky. What I do think is more probable is that the 12v BMS and/or DCDC converter detects no battery and halts but even that would make me ask more questions like why?

Yes, when he said he disconnected the battery and the truck turned off, I wondered what wires he removed from the battery and why the DC-DC converter did not keep the truck powered with the wire or wires removed.

Maybe the load was too much for the DC-DC converter without the battery?
Or maybe somehow that disconnected the DC-DC converter when he disconnected the battery?

It would make sense that the DC-DC converter would be grounded with or without the battery connected to the system ground, so you are probably right, which means I guess the reason the truck turned off was the load was just too much for the DC-DC converter to carry.

The DC-DC converter and the battery (neg via the BMS sensor) would be in a parallel connection with the rest of the 12v system.

But I thought, maybe where the negative is connected to the BMS sensor is a junction point where the DC-DC-converter is connected to a separate wire that goes to the truck ground, and that might have been disconnected when disconnecting the battery.

From the outside it looks like one big wire and connector to the BMS sensor but I haven't removed it to be sure.

Without wiring diagrams or dissecting it myself, a lot of guess work.

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[chriserx]

I'm gonna go do some testing this week with my power supply acting as the battery, if you haven't heard from me by Wednesday, PM spam me until I do it

 

[El Duderino]

My experience with boost and buck converters is they use a 12v signal line for enable and if you remove the 12v source (battery in this case), it shuts off the converter instantly. I would say that is case with a Lightning also.

 

[elizarrj]

I got my truck back today from the dealer. As suspected, they found the 12 Volt battery was bad. They checked everything behind it, and all checked out. Hopefully, my issue is resolved. I did take my battery checker with me, as I suspected the battery would be low due to transit, long time on shelf, etc. The battery did test low. So, I took the truck for an extended drive and came home and put on my trickle charger. It did charge for like 30 seconds and then went green. The Battery Maintainer I got was a Noco Genius 1. The battery appears to have charged up during my drive. Finger crossed.

 

[ScottC]

I feel like i'm 24 hours behind you with round two at a Dealer. Towed my car on Friday before the holiday weekend. They said batt was dead (again) and charged it (again). I'm having them hold onto it and recheck it for a couple days. Good luck.

 

[elizarrj]

I feel like i'm 24 hours behind you with round two at a Dealer. Towed my car on Friday before the holiday weekend. They said batt was dead (again) and charged it (again). I'm having them hold onto it and recheck it for a couple days. Good luck.

Well, that is a bummer. I hope they find what is really causing the issue.

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