What a Conundrum - Very low Voltage to Cab

[Diablo106]

We have a 2020 Ram 1500 Bighorn with an eTorque 5.7L hemi engine.

Now the issue:
Dash does not light up and neither does the ignition switch - fresh new 12 volt battery but the 48V battery is totally dead with a new one on order. Only getting 1.6V on high current fuses N3 and N4 as well as at the main functions in the cab going to all of the modules. Can shoot power (with a power probe) to one of the fuses for the main functions and get unit to start.

Some of the other fuses in the cab get the full 12 volts ie. Horn and cargo light

Anyone ever dealt with this before?

 

[BossHogg]

There isn't much troubleshooting info in your post. My first suggestion and this comes from watching YT videos and reading posts with similar issues, is check grounds.

 

[DanAR]

Most of the equipment including the starter run on 12 volts so it should start with a good battery. But the generator that restarts the motor in stop/start mode works off the 48 volt battery and also through a step down converter I guess, charges the 12 volt battery. I’m not sure what else might run off of 48 volts other than the converter and relays for the stop/start. So I don’t think you will go far with a dead 48 volt battery unless the generator will still power the converter with a dead 48 volt battery.

Just speculating - there’s a lot of electronics and crap in one of these.

 

[markabby]

We have a 2020 Ram 1500 Bighorn with an eTorque 5.7L hemi engine.

Now the issue:
Dash does not light up and neither does the ignition switch - fresh new 12 volt battery but the 48V battery is totally dead with a new one on order. Only getting 1.6V on high current fuses N3 and N4 as well as at the main functions in the cab going to all of the modules. Can shoot power (with a power probe) to one of the fuses for the main functions and get unit to start.

Some of the other fuses in the cab get the full 12 volts ie. Horn and cargo light

Anyone ever dealt with this before?

where are the "N" fuses? all i see are "F" ones.

oops....never mind.

 

[Diablo106]

There isn't much troubleshooting info in your post. My first suggestion and this comes from watching YT videos and reading posts with similar issues, is check grounds.

This is what I've done so far:
Checked all grounds in the engine bay, on the chassis, and in the cab
Pulled each harness one at a time to see if breaker stops tripping on power probe (probe showing voltage going up to 24V on the circuits with low voltage) and determined that there is an issue in the main cab harness (can't tell if it's one of the modules and wasn't sure if it would be anything to do with the battery module in the back)
I tried to get a Schematic for the cab and a list of circuit specs so I could figure out which circuit is being overloaded to see if that was causing the voltage drop but mitchell1 ProDemand didn't have much info and the dealers were of no help

 

[Diablo106]

Most of the equipment including the starter run on 12 volts so it should start with a good battery. But the generator that restarts the motor in stop/start mode works off the 48 volt battery and also through a step down converter I guess, charges the 12 volt battery. I’m not sure what else might run off of 48 volts other than the converter and relays for the stop/start. So I don’t think you will go far with a dead 48 volt battery unless the generator will still power the converter with a dead 48 volt battery.

Just speculating - there’s a lot of electronics and crap in one of these.

I know most of it runs off of the 12V system, but I was under the impression that the 48v battery module also tied into the main cab harness (the harness that goes to the stereo, instrument panel, etc.) I'm wondering at this point if the module is shorted out and causing a massive draw/short on the main cab harness

 

[BossHogg]

It looks to me like you have done about all you can and now need to graduate to the schematic level of circuit tracing. This is so frustrating, and even more so for those who have the skills to troubleshoot at the schematic level. We can't get a schematic; if we do, there is no guarantee we have the correct information.

I watch Eric O from the South Main Auto channel on YouTube. In my years of automotive, this guy is in the top 1% of troubleshooting smarts, and he is equally frustrated by the wrong information he gets from his PAID subscription services.

The question is, where do you go from here? The dealer? You will likely pay for a lot of wasted diagnostic attempts without a cause of the issue. I don't think many dealers have truly qualified and trained service techs. My dealer, who is no longer a preferred dealer, once had a really good tech, he worked on both my diesels and he was very competent, so much so he didn't have to put up with dealer BS and moved on.

Your option may get to the point where a trade and purchase is the best way forward.