2018 579 low voltage disconnect

Discussion in 'Peterbilt Forum' started by Edjahman, May 19, 2020.

  1. pushbroom

    pushbroom Road Train Member

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    LVD is not cecu controlled on your truck. Might not even have one.
    LVD does not have anything to do with the starting circuit anyway,

    The starting circuit goes through a start enable relay that the CECU controls. If voltage drops to the cab the relay trips and power gets cut to the starter. Once that happens the dahs gets full power again so it sends it to the starter then gets low voltage and trips the relay. Hence the click click click.

    Root cause is too much voltage drop to the cab. Clean the cab grounds and powers at the starter and up on the firewall cab mega fuse box.

    You can also pop the speedo and tach panel and bypass the cecu controlled start enable relay. This will let the engine crank til there is no battery juice left regardless of the voltage to the cab. You can jump it with spade terminals and a short piece of wire. The fuse panel lid will id the relays behind the speedo/tach.
    After you jump it only the key controls the start circuit and the CECU cannot intervene for starter overheat/ rpm starter disable.

    20210204_155237.jpg
     
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  3. Roberts450

    Roberts450 Road Train Member

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    @pushbroom cool. Thank you so much. That’s exactly what’s happening. Truck does have an LVD tho as it will cut power to the cab n sleeper if I leave the fridge on over the weekend. Had a 2WS swapped in last year after bad tuning hurt the x15 so dont need all that starter interrupt stuff but mostly I think its the crappy volvo branded batteries that got put in the truck but I’ll be checking over everything this weekend.
     
  4. pushbroom

    pushbroom Road Train Member

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    Bad batts/ dirty connections can for sure cause that but it aint a bad idea to bypass the relay.
    How bad did the X15 blow? Running a converter so the 2ws can talk to the CECU?
     
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  5. Roberts450

    Roberts450 Road Train Member

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    Yeah. I got everything from Kustom Truck since they are in my back yard. The x15 started pushing coolant out of the over flow so it might have just been an egr cooler failure but the sudden dropping of a cylinder was my deciding factor. It still ran but only on 5 with lots of blue/white fuel smoke so most likely just an injector failure but was never really happy with the tuning. Still have the engine and one day I’ll tear it down to find out what went wrong. Ran way to much boost all the time and just sounded way over worked even with just an empty trailer at 65 on the freeway. Only thing I miss is the jake power. The cats getting ruffly .2-.4mpg better then the cummins doing the same work. Had Kustom rate it at a 550. Dont know the exact file but she has just a hint of smoke on the shifts and pulls 28-30psi and 850-900 degrees so Im sure its not a factory tune.
     
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  6. Roberts450

    Roberts450 Road Train Member

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    @pushbroom i feel like a noob. I gave ya my DOT number not my vin the other day. Try 486218 to see about my LVD. Numbers are right above each other on the truck n I looked at the wrong one. Not that is has anything to do with my starting issues but be curious how the LVD is controlled still.
     
  7. pushbroom

    pushbroom Road Train Member

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    It has the LVD module installed to the left of the steering column. Not cecu controlled.
     
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