Need guidance diagnosing DEF heater line #3 open circuit

Discussion in 'Kenworth Forum' started by tiddlytanker, Nov 21, 2020.

  1. tiddlytanker

    tiddlytanker Light Load Member

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    May 4, 2017
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    I had code SPN 4356/FMI 5 pop up on my T680 with a mx-13 engine. It seems to be an open circuit code for line #3 (its labeled C on the electrical connector). I went out an bought a multimeter to try and diagnose.

    I am not getting any voltage from the connectors on the problem line or good lines. Maybe I am using the multimeter wrong?, i have never used one before. Im guessing the truck only sends power when it needs to be heated? I did see videos of people getting 12v and 3v on each of the pins but can not find anyone doing it with paccar.

    For resistance I am getting 5ohms on the problem line and around 14 on the two good ones. Does anyone have any way to know the specs for this? Can't find anything at all for paccar online. Closest thing I found is this 804-12.pdf - SPN 4354/FMI 5, SPN 4355/FMI 5, SPN 4356/FMI .EPA10, DDEC VI, DD13, DD15, DD16, SPN but its for detroit.

    The part number for the hose is: M50-6031-71132200
     
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  3. AModelCat

    AModelCat Road Train Member

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    A lot of modern electronics will not send any voltage into a circuit if the ECM detects an open or short in the circuit. Thus if you unplug a circuit to check for power, you will not see anything. You'd have to backprobe the connector with spoons so that the connector can remain connected.
     
    tiddlytanker Thanks this.
  4. tiddlytanker

    tiddlytanker Light Load Member

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    Minot, ND
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    Makes sense, at some points I did see it 7 volts flash on my multimeter every few seconds (happened on the good connector too). Which makes me think maybe the truck was probing to see if something was connected. Probably going to end up letting the shop deal with it. Need to take it in for recall work anyways.
     
  5. QUALITYTRUCK

    QUALITYTRUCK Road Train Member

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    Set your meter where it will "beep" when you touch the probes together. Now unplug the line in question and touch the 2 probes to each of the 2 contacts(on the line, not the truck side) If it beeps then line is good. No beep, then replace heater line.
     
    spsauerland and tiddlytanker Thank this.
  6. tiddlytanker

    tiddlytanker Light Load Member

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    May 4, 2017
    Minot, ND
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    Pretty sure the heating line has a complete circuit. So its either the harness that powers it or it just came lose somehow and triggered the code. From experimenting with the other heaters, once the code is tripped it wont go away on its own. Going to have the codes cleared tomorrow and see what happens
     
  7. tiddlytanker

    tiddlytanker Light Load Member

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    May 4, 2017
    Minot, ND
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    The next day I when I started the truck all the codes cleared, including the ones I set off testing the other cables. 2000 miles later and I have no faults.
     
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