Medium and Heavy Trucks
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On the code the MID 128 is engine, the SID 231 IS THE J1939 control circuit, FMI 8 is electrical fault. So the engine is saying it can't talk to other ECM's or it can't hear them. The twisted green and yellow wires are the data link (J1939) circuit. I need you to check these wires in the inside cab diag plug. The pins are labeled "C" & "D". with the key off and using a multi meter in the ohms position you should have 60 ohms. If you have more or less there is a fault in that circuit, either a green or yellow wire rubbed thru or broken wire or another faulty ECM is interrupting the circuit. It's a hard job but most likely it's outside of the bulkhead and you have to trace the 2 wires from the pass thru at bulkhead all the way to the Engine ECU. You have to take time and inspect very carefully.
The VECU & EECU either work or they don't, there is nothing in the middle.
I hoped this will help you and please rate my help for you today,
Now if you have 120 ohms on the data link there is a resister missing. It looks like a gray plug the has no wires coming out of it. It plugs into the j1939 harness in the fuse & relay center. So there is a twisted yellow & green wires with a plug with nothing plugged into it. thats where the resister goes. Its about 1 inch long and gray. Sometimes they don't clip and fall out. See if you can find it or go to the dealer and buy one. There needs to be 2 of them in the circuit, 1 in eecu and one in fuse & relay center. Thats how we get 60 ohms in the circuit. That is the first step and has to be corrected before starting on anything else.
This is what the terminating resister looks like. Its light gray and about 1 inch long and about 1/4 inch wide.
It should be in with all the wiring and fuses and relays.
Here is the locations of the newer style resisters, I will send a picture of the new style resisters
new style resister
I'm not sure which style you have in this truck. It's near the time that they changed over.