Powerboost - Totally Dead

[FaaWrenchBndr]

Replaced main battery first before even knowing of the small 2nd battery. It is reading around 12.7v - 12.8v consistently.

OK, did you reset the BMS after replacing the main battery?

Sponsored

 

[FaaWrenchBndr]

That battery is fine and strong 12.8v. But it is like a dead brick without that small battery voltage higher. Nothing works, can't jump, can't do anything.

pull the small battery out and put it on a charger. You have other problems, whether it be a blown fuse or like mentioned before the isolator being blown. For some reason that small battery is not getting charged.

I would strongly suggest you not attempt to, jumpstart by connecting to that small battery . Charge it and then get to a shop.

 

[dejoli]

OK, did you reset the BMS after replacing the main battery?

Yes. If I pull the small battery, charge it back up to 12v, it works great and as it should. No issues starting, etc. Both electric and ICE. Starts runs, drives normal.

But just letting it sit, the small battery drains and then nothing again.

 

[HammaMan]

I would not jumpstart that small battery. It is not for starting the engine. It is for maintaining voltage for electronics while you are in electric mode.

The battery in the engine compartment is what needs charged and/or jumped

The small batt is simply a transient buffer for the DCDC and is only separated from the under-hood batt during rolling starts for ~1 second. Both batts remain in parallel all other times and putting a charge to either of them charges both of them. The aux batt is best thought of as a capacitor with a tiny bit of reserve capacity while the truck sits.

The PB is moreso awakened than jump started. 'Parked' starts are performed by the traction motor via the HVB. The only situation where the flywheel starter would be used is if the truck had a depleted HVB by being left in the accessory key position (uses HVB/DCDC to provide 12v power until the HVB hits ~41% SOC) -- If it was parked hot, and left in accessory until the HVB hit 41%, when the battery cools down overnight and becomes less excited / registering lower SOC, only then will the flywheel starter engage. If the HVB SOC reaches 35% the truck won't do anything and goes into stop safely now, aka tow to the dealer, and wants an external HV charger connected to bring up the HV SOC. (this was the last known logic, subsequent updates may have changed this lower threshold) -- It should also always be assumed it needs to perform a flywheel start. The aux batt isn't an easy area to connect up to with cables. It doesn't matter either way where a charger is connected. There are 2 125a fuses on the aux batt's 4ga wire -- the one in the BCMC may not be serviceable. I've taken it apart and found no way to remove that fuse, though I didn't try to (service manual indicates the fuse is serviceable). There were no obvious indicators as to serviceability when it was removed.

 

[nitrobass24]

Something is killing the aux battery, but the truck should still start with it disconnected. I'd check all of your fuses before going to the dealer. I had several that were not pushed in all the way from the factory.

 

[dejoli]

Something is killing the aux battery, but the truck should still start with it disconnected. I'd check all of your fuses before going to the dealer. I had several that were not pushed in all the way from the factory.

Checked all of them. Couldn't find anything blown, many were loose/not pushed in all the way. So pushed them all in. Disconnected or with the low voltage, truck will not start. Lights don't work, walk up sentry doesn't work, no dash lights, it's truly a brick without the aux battery charged.

 

[dejoli]

The small batt is simply a transient buffer for the DCDC and is only separated from the under-hood batt during rolling starts for ~1 second. Both batts remain in parallel all other times and putting a charge to either of them charges both of them. The aux batt is best thought of as a capacitor with a tiny bit of reserve capacity while the truck sits.

Charging the main battery did nothing to the aux battery. Left charger on main overnight and aux was still reading 3.2v. Pulled and charged it and within a couple hours, was up to 12v. put it back in, started right up. Then would drain. Main battery is not draining. Just the aux battery.


If it's low (under 10v), it's not starting, no lights, etv.above 10v on the aux will start/function as normal.

But with the aux low, nothing works and it's draining in 24 hours to less than 3v. Main battery is still 12.8v while the aux drained out.

 

[FaaWrenchBndr]

Yes, that is crazy, the rear battery is essentially just an ox battery. It gets charged the same way that the main battery has charged. There is an isolator. Did you check the fuse at the rear battery?

 

[HammaMan]

Charging the main battery did nothing to the aux battery. Left charger on main overnight and aux was still reading 3.2v. Pulled and charged it and within a couple hours, was up to 12v. put it back in, started right up. Then would drain. Main battery is not draining. Just the aux battery.


If it's low (under 10v), it's not starting, no lights, etv.above 10v on the aux will start/function as normal.

But with the aux low, nothing works and it's draining in 24 hours to less than 3v. Main battery is still 12.8v while the aux drained out.

Did you play with the battery isolator module? It's sitting beside the under hood batt. I discovered early on if some modules are disconnected / not powered / cannot talk to the bus, the truck will drain the batteries entirely to dead. In my case I'd connected the massage seats to a switched circuit and that was enough for modules to not sleep and it'd completely drain the batteries.

The fact that your batts had different voltages is a clear sign of an issue as they're always connected together.

 

[scott011422]

For whatever reason, it sounds like the battery isolator is bad. Its not being tied back into the underhood battery. Or something else like a bad wire or connection. But there is no connection there to see 2v at the aux and 12+ under the hood. So your aux is the only thing powering the truck electronics. Which is why its getting sucked down so fast and why the truck is a brick when it dies.

 

[dejoli]

I have not played/checked the isolator. Is it obvious when looking at the battery where it's at?

Like I shared at the beginning too. When the aux battery was reading 3.2v - the live side of Fuse 1 was also 3.2v, whereas the input on the main fuse block was 12.8, as was the battery as well. Would this point back to an isolator issue as well? My dealer is an hour away so avoiding going down would be good.

 

[scott011422]

I have not played/checked the isolator. Is it obvious when looking at the battery where it's at?

Like I shared at the beginning too. When the aux battery was reading 3.2v - the live side of Fuse 1 was also 3.2v, whereas the input on the main fuse block was 12.8, as was the battery as well. Would this point back to an isolator issue as well? My dealer is an hour away so avoiding going down would be good.

Yes, Its attached to the left side of the underhood battery. You'll see a large red wire going from the battery to it.

 

[dejoli]

So just ran and tested it again quick. When I pull the aux battery, I get nothing. No lights, can't start, no dash lights. Truly just dead.

In the fuse block, I get 12.7 volts on the mine line in and the other 4 side outputs are at essentially 0. When I had the aux battery hooked up, those would read the same voltage as the aux battery.

isolator is connected and wires are tight. Not sure what else I could test on that?

 

[HammaMan]

So just ran and tested it again quick. When I pull the aux battery, I get nothing. No lights, can't start, no dash lights. Truly just dead.

In the fuse block, I get 12.7 volts on the mine line in and the other 4 side outputs are at essentially 0. When I had the aux battery hooked up, those would read the same voltage as the aux battery.

isolator is connected and wires are tight. Not sure what else I could test on that?

Ambiguous language, take a pic and notate what you're trying to say.

Check continuity between studs in the BCMC as well

 

[scott011422]

Thats odd then. Because there is a fuse for the AUX battery (F212) and if that were bad, Your truck wouldnt do anything different if the battery were charged. So that fuse has to be good. I'm still leaning toward your isolator. There is a short red wire that goes from the underhood battery into the top of the isolator. There is another red wire that comes out of the bottom, Does the voltage on that bottom wire match the voltage of that underhood battery?

According to the diagram, your junction box isn't getting power from the underhood battery.

Basicly the way it works is the BISG, flywheel starter and BMS Sensor are all driven directly off of the underhood battery. Both batteries are tied into the junction box. During starting events the Isolator disconnects the underhood battery from the junction box, leaving the entirety of the rest of the truck to run off the AUX battery for the duration of the cranking event.

For whatever reason, you are not seeing that connection from the underhood battery to the junction box. Unless the junction box went bad.

Sponsored