Failed cabin heater kills 12 volt

[Ragman]

Had one of our trucks die right after started (about 10 minutes into shift) 12v dead - swapped in new one. Left in heated shop overnight started next morning fine drove 10 minutes dead again.

Swapped in second incase first was bad - no luck truck would go in Accessory but not start. A couple minutes then that battery was dead.

Stuck a 25 amp charger on it and could keep it “alive” but not start. Charger off, truck instantly dead even with new 12 volt.

In the dealer now, told cabin heater issue draining power - $2k fix (off warranty). Never seen a battery killed that fast one heck of a drain/short.

Truck was at 100% charge coming off a LV2 - ambient about -10F - truck has ~80k miles - 23 SR XLT.

First actual repair across fleet so far.

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[ElectrifyingMe25]

Had one of our trucks die right after started (about 10 minutes into shift) 12v dead - swapped in new one. Left in heated shop overnight started next morning fine drove 10 minutes dead again.

Swapped in second incase first was bad - no luck truck would go in Accessory but not start. A couple minutes then that battery was dead.

Stuck a 25 amp charger on it and could keep it “alive” but not start. Charger off, truck instantly dead even with new 12 volt.

In the dealer now, told cabin heater issue draining power - $2k fix (off warranty). Never seen a battery killed that fast one heck of a drain/short.

Truck was at 100% charge coming off a LV2 - ambient about -10F - truck has ~80k miles - 23 SR XLT.

First actual repair across fleet so far.

Did anyone at the dealership explain how the failing cabin coolant heater could cause a large drain on the 12V battery.

For sure the cabin coolant heater is powered from the HV battery. I guess the controls inside the cabin coolant heater module that control the heater use 12V and maybe a relay or solid state component shorted inside that caused the drain.

I just had my cabin coolant heater replaced a few weeks ago, and all is good now. 23, XLT. There was a recall on the '21 - September '23 Trucks. I didn't have any issues with my 12V battery.

I remember reading about issues with coolant valves, associated with the heater, sticking and causing issues. I wonder if a sticky valve could have been draining your battery. When solenoids in valves are energized and if the plunger doesn't shift, the coils can short. I can see where a shorted coil would drain your battery quickly.

It would be nice to learn what the dealer had to replace. Maybe take a look at your invoice. I wonder if they changed the heater and the valve. They only changed my heater module to fix mine.

Luckily, mine was under factory warranty. But, the invoice showed it would have been over $1000.00 if i would have had to pay.

 

[chl]

Some kind of short circuit in one of the resistive heater elements or a bad blower motor/pump will kill a 12v battery PDQ. The stuck valve issue mentioned above will also put a lot of strain on the pump motor. The heating cooling system on the Lightning has a lot of places where things could, and apparently, do go wrong. A lot of plumbing!

These are a heavy load to begin with, but when they go bad, watch out!

But I wonder if you might also have a problem with the DC-DC converter and the BMS that is supposed to maintain the 12v battery?

When you get it back, watch out for that - and keep it on a trickle charger anyway.

 

[TaxmanHog]

The PTC is powered by the 400v HVB.

Something else related to the 12v controls is the culprit.

 

[chl]

The PTC is powered by the 400v HVB.

Something else related to the 12v controls is the culprit.

Yes I just looked that up...

So now I wonder, what did the dealer mean about the cabin heater being the issue?
The electric pumps that push the heat/coolant around I suppose?
The blower too, maybe?
The heated seats I suppose are resistive heat on the 12V system?

It would be nice to have a complete set of wiring diagrams for the Lightning 12V system.

A $2k fix sounds like a very involved repair...

 

[ElectrifyingMe25]

Yes I just looked that up...

So now I wonder, what did the dealer mean about the cabin heater being the issue?
The electric pumps that push the heat/coolant around I suppose?
The blower too, maybe?
The heated seats I suppose are resistive heat on the 12V system?

It would be nice to have a complete set of wiring diagrams for the Lightning 12V system.

A $2k fix sounds like a very involved repair...

I wouldn't be surprised if the cabinet coolant heater was changed first, and then the $20.00 part that really fixed it.

Look at your invoice to see what parts were sold to you.

Good Luck.

 

[chl]

I wouldn't be surprised if the cabinet coolant heater was changed first, and then the $20.00 part that really fixed it.

Look at your invoice to see what parts were sold to you.

Good Luck.

Yes that would be interesting to see from the OP.

The OP said "the dealer...told cabin heater issue draining power - $2k fix (off warranty). Never seen a battery killed that fast one heck of a drain/short...."

What was killing the 12V battery...

If a cooling system valve failed, perhaps it cause damage to the DC-DC converter - if the DC-DC converter went down, no charging the 12V battery...but could it have actually push the 12v battery to the damage point? Hard to imagine that. And you would think there would all kinds of safety error messages if a cooling system valve failed.

I think I read that there have been LV BMS system components fail, and there were recalls about that.

I wonder what exactly the $2k repair involved?

Had one of our trucks die right after started (about 10 minutes into shift) 12v dead - swapped in new one. Left in heated shop overnight started next morning fine drove 10 minutes dead again.

Swapped in second incase first was bad - no luck truck would go in Accessory but not start. A couple minutes then that battery was dead.

Stuck a 25 amp charger on it and could keep it “alive” but not start. Charger off, truck instantly dead even with new 12 volt.

In the dealer now, told cabin heater issue draining power - $2k fix (off warranty). Never seen a battery killed that fast one heck of a drain/short.

Truck was at 100% charge coming off a LV2 - ambient about -10F - truck has ~80k miles - 23 SR XLT.

First actual repair across fleet so far.

I wonder what exactly the $2k repair involved?

Show us the invoice...

Did you reset the BMS after replacing the battery each time?
There is a procedure for that, the BMS has to be reset or the system will not know you replaced a dead battery with a charged on and will load shed thinking the battery is dead.

Very strange.

 

[Ragman]

The invoice was $2,300 and is securely locked in dead truck at dealership - I just went to pick it up.

Yes did the BMS reset dance - 5 hi beam flashes and 3 brake taps or whatever - the dash icon showed the reset each time.

Stay tuned….

 

[chl]

The invoice was $2,300 and is securely locked in dead truck at dealership - I just went to pick it up.

Yes did the BMS reset dance - 5 hi beam flashes and 3 brake taps or whatever - the dash icon showed the reset each time.

Stay tuned….

So...the PTC (heater) is powered by the HVB when the truck is on at 400VDC+

The HVB is also connected to the DC-DC converter to step it down to 12VDC for charging the 12V battery and powering 12V things in the truck.

The charger on the truck takes incoming 240VAC and changes it into high voltage DC providing it to the DC-DC converter and the HVB.

The PTC (heater) also uses this high voltage DC for power, so it must be in parallel with the HVB input to the DC-DC converter and the battery from the charger output.

If the PTC had a short, I suppose the high current could damage the DC-DC converter - I remember seeing in a video somewhere that the DC-DC converter connection is used as a junction point for the high voltage output from the charger. But I don't see how that would affect the 12V battery.

The wiring is under the floor of the frunk (see this video: )

The input J1772 240VAC goes in from the charge port to a charger where it is converted into high voltage DC (rectified and stepped up) and the DC output goes to junction point on the DC-DC converter where it is split and:
1) goes to the input of the converter to be stepped down to 12VDC for charging the battery and powering the 12V truck components and
2) is routed toward the back of the truck and into the high voltage battery to charge it.

Now somewhere on the way to the HVB, the PTC is also connected to the high voltage DC.

That's why the PTC can:
1) be powered by the HV battery when the truck is on or being charged and the battery contactors are closed, or
2) be powered by grid power through the charge port when connected to an EVSE to keep the battery warm if needed and
3) precondition both the battery and the cabin if programmed to do so.

So maybe what went wrong in the heater was some electronic swithc/relay got stuck so that when the truck was off and not being charged (HV not connected to the PTC or DC-DC converter), and was not on an EVSE to get grid power, it somehow drew power from the 12V battery though the DC -DC converter.

That should not happen. The DC-DC converter should be a one way converter not a bi-directional converter that can run in reverse drawing power from the 12V battery into the heater on the high voltage line.

But who knows, maybe the DC-DC converter is bi-directional? Or maybe it has an internal problem causing it to be a two-was street?

I am just not seeing any other way the bad PTC could draw down the 12V battery yet.

Very curious!

 

[chriserx]

I can't say for certain, but I also think that it's likely that the PTC has a 12v input for it's electronic controls. If I'm right, this could be where the draining of the 12v would be occurring, if anyone has a wiring diagram to post we can use it be definitive.

 

[chl]

I can't say for certain, but I also think that it's likely that the PTC has a 12v input for it's electronic controls. If I'm right, this could be where the draining of the 12v would be occurring, if anyone has a wiring diagram to post we can use it be definitive.

Yeah I wonder about that...hard to get the full picture without wiring diagrams...there is a lot of wiring under the hood in these vehicles.

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