Where does the truck measure its voltage from?

Discussion in 'Volvo Forum' started by loudtom, Dec 25, 2020.

  1. loudtom

    loudtom Road Train Member

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    The truck is a 2012 VNL. The reading from the alternator is 14.2v, and at the batteries it is 14.1v, but the dash can display anywhere between 12.8-13.8v. I've tightened all of the battery terminals and the ground from the battery, as well as the starter lugs. There was one morning that the low voltage warning happened, but the inverter was still getting over 12v, and the truck showed no hesitation when it started up. Everything else works like it should, no codes or problems, it just gives a false reading. Which wire or component should I look at next?
     
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  3. Snailexpress

    Snailexpress Road Train Member

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    Two big wires and studs on the firewall. Buried under air lines. Outside and inside connections. From there to power distribution bus where are fuses.
     
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  4. loudtom

    loudtom Road Train Member

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    I checked the voltage on those studs when I replaced the trailer supply pass through fitting, and it came back fine. I guess I'll have to check the wires coming off of them.
     
  5. flood

    flood Road Train Member

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    the low voltage alarm is set for 12.2
     
  6. loudtom

    loudtom Road Train Member

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    This was the 11.6 one or whatever, where the sleeper lights don't work and the LEDs on the switches start flashing. I've got my own inverter off the batteries that I wired into the power outlet, so it doesn't get affected by the truck's voltage cut out. It shuts itself off when it gets low, and it gets its reading directly from the battery.
     
  7. silver dollar

    silver dollar Medium Load Member

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    I'm having the exact same problem on my '04 VNL. I finally gave up on it. If and when you find the problem, please post it. Thanks
     
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  8. 401-Alex

    401-Alex Light Load Member

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    I have an 05 vnl 670 same deal new batteries. Random low voltage alarm even after 10 minutes of a full days drive. Truck also randomly just clicks when you go to start it like a bad starter. I have new starter ,new ignition switch,New battery cables, new starter solenoid. Truck always starts just sometimes takes 2 turns of the key
     
  9. Inderjit

    Inderjit Light Load Member

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    On the left side of the firewall where all the air and electrical enter the cab.
    There are two brass studs on the pass-through panel where the power and ground
    go into the cab. make sure they are clean tight inside and outside. At the top
    of where the pass-through panel is bolted to the firewall there are several ground studs.
    Make sure the connections are clean and tight.
    Follow the two cables from the power and ground at the pass-through panel and
    make sure the other end of both cables have a clean tight connection.
    Do you have a battery disconnect switch? if so make sure the connections on it are good as well.
     
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  10. loudtom

    loudtom Road Train Member

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    Cleaning the grounds and tightening them up got me up to 13v, but cleaning the positive ends got me back up to 14v. However, the maxi fuse connected to the truck was the main problem. It ended up vibrating loose internally or something, so when the truck went over a bump, it would lose all of its power. After removing the fuse and running directly to the battery, it hasn't shut down or lost power, but I do suspect that cable end is going to need to be cut and a new end crimped on it. The voltage now runs between 13.7-14.0 without any HVAC or lights running.

    I had to cut off the wires to the original fuse because the nuts were rusted to it. The one I used to replace it was a cheap one, so the plastic housing fell apart and the copper inside split. I'm also going to focus on securing my cables better so they won't move around or vibrate as much.
     
    Last edited: Feb 4, 2021
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  11. silver dollar

    silver dollar Medium Load Member

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    Thanks for posting this. But, I'm not familiar with the maxi fuse that you speak of. Where is it located?
     
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