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many def and dpf codes

Discussion in 'International Forum' started by Ed's Bus Shop, Dec 30, 2025.

  1. Dec 30, 2025 #1
    Ed's Bus Shop

    Ed's Bus Shop Bobtail Member

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    Dec 30, 2025
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    Hello. I am looking for help with my 2017 IC ce300 school bus with a Cummins ISB engine. I am getting many DPF, DEF, and also VGT codes. I already switched out the DEF sending unit witch I have had problems with in the past. Can anyone help figure this problem out?
    OEM CODE 1894, 6688, 3868, 6652, 3232, 2771, 4152, 4151, 5177, 4677, 4572, 6613, 3714
    I tried clearing the codes and all of them came back with key on engine off.
     
    Last edited: Dec 30, 2025
    Ed's Bus Shop, Dec 30, 2025
    Ed's Bus Shop, Dec 30, 2025
    #1
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  3. Dec 30, 2025 #2
    Heavyd

    Heavyd Road Train Member

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    All those codes are components not communicating to the engine. They all share the same power supply except for the VGT. When you have a bad power supply, the VGT will not be included because it has a different power supply. After that they all share the same communication wires. Now welcome to one of the most complicated diagnostics in commercial trucks there is. Datalink troubleshooting. With the key off you should have about 60 ohms of resistance between the yellow and green wires at any sensor connector that is coding. Find one you can get to easily and check there. DO NOT use the turbo VGT. If you are getting 60 ohms, then it is possible a sensor has failed and it is corrupting the data on the whole network. The only way to find this is to unplug a sensor one at a time to see if the rest of the codes go inactive. 90% of failed sensors are Nox sensors, so I would start with those.
     
    Heavyd, Dec 30, 2025
    Heavyd, Dec 30, 2025
    #2
    QUALITYTRUCK, dosgatos and Ed's Bus Shop Thank this.
  4. Jan 8, 2026 #3
    Ed's Bus Shop

    Ed's Bus Shop Bobtail Member

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    Dec 30, 2025
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    Sorry it took so long to get back to you. I measured ohms across both NOX sensors and only had 11 ohms. Started unplugging sensors and found when i unplugged the VGT Actuator and all my DPF and DEF code went inactive. I ordered a new actuator just waiting to see if this fixes the problem.
     
    Ed's Bus Shop, Jan 8, 2026
    Ed's Bus Shop, Jan 8, 2026
    #3
    Heavyd Thanks this.
  5. Jan 10, 2026 #4
    Heavyd

    Heavyd Road Train Member

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    The VGT has the other terminating resistor built into it, so with it unplugged, you should get 120 ohms across the datalink pins. With all the other sensor codes going inactive, I think you found it. The VGT actuator is also a high fail item.

    Keep us posted!
     
    Heavyd, Jan 10, 2026
    Heavyd, Jan 10, 2026
    #4
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