2018 dash misreporting battery voltage on ACC

[MoParts]

Laramie, premium dash. I was outside a welding supply shop waiting for them to open first thing in the morning and listening to music on the 8.4 uConnect system/USB input. I had the key on ACC. Just for S&G I cycled through the display, which I normally keep on coolant/oil/trans temp, to look at the fuel filter and oil life displays. I was a bit surprised to see that those were not reporting properly but chalked that up to possibly the ECU being off. What really surprised me is that the voltage readout said "<8v". I started the truck and it went right to 13v then 14v. Both batteries were new in mid-2020 when I bought the truck and I have never seen any symptoms of weak battery.

Can anyone shed any light on this? Are we unable to monitor actual battery voltage on these systems with the key in ACC position?

 

[csuder99]

Yup. The battery voltage is not measured by the instrument cluster but the PCM which in turn sends the info to the cluster. With the PCM off there are no messages to update the cluster and the cluster shows a programmed default. You should see the correct voltage with the key in "run" but the engine not running though.

 

[MoParts]

Hmm. Thanks, I suspected as much. I've sat and listened to music much longer and was just a bit shocked when I saw that.

 

[BossHogg]

What the designers should have done is to show no voltage if an accurate reading isn't available. My 2015 3500 does the same thing which, at first, scared me and forced me to measure the battery voltage which read normal. I just picked up a 2022 RAM, I'll have to see if the battery voltage reported still behaves the same.

 

[MoParts]

Agree. Gone are the days when the voltmeter was a bit of wire wound around a core and swinging a needle, which always reflected reality(more or less)...