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farmtrucknw · 05-01-2026, **(Subject: Spn5746 fmi 4 )**

I have a 2017 Prostar I'm trying to track down what's making it throw this. The cummins code is 4156. Ive been looking for broken wires, run continuity tests on wires and checked and changed fuse and relay in the def pdm behind def tank. Doser injector ohm out OK. Any help appreciated.

Rawze · 05-02-2026, **(Subject: Spn5746 fmi 4 )**

What is the engine ser#?

fault 4156 is for the DEF heater relay coil/circuit, and not for the Doser unit itself.

farmtrucknw · 05-02-2026, **(Subject: Spn5746 fmi 4 )**

79915243

(05-02-2026 )Rawze Wrote: What is the engine ser#?

fault 4156 is for the DEF heater relay coil/circuit, and not for the Doser unit itself.

farmtrucknw · 05-19-2026, **(Subject: Spn5746 fmi 4 )**

Any help on this? Would one of the line heaters cause it to throw this?

Rawze · 05-19-2026, **(Subject: Spn5746 fmi 4 )**

(05-19-2026 )farmtrucknw Wrote: Any help on this? Would one of the line heaters cause it to throw this?

maybe monitor the input using Insite software?.

farmtrucknw · 05-21-2026, **(Subject: Spn5746 fmi 4 )**

Finally got my own Insite set up. I noticed in there under features and parameters I can disable the doser unit heater relay. I did that and I can clear my codes and my derate condition. My assumption is that will be fine in warmer weather like now but won't work well in the winter and I'll be back to looking for the real problem?

farmtrucknw · 05-25-2026, **(Subject: Spn5746 fmi 4 )**

So disabling didn't work but I finally was able to track down this corroded wire and got this fixed properly. I don't know why this gave me so much mental gymnastics but i just had to trust what that code was telling me. Something is wrong in that relay circuit. How it had a break in the wire and corrosion like it did i have no idea.

Rawze

(05-25-2026 )farmtrucknw Wrote: So disabling didn't work but I finally was able to track down this corroded wire and got this fixed properly. I don't know why this gave me so much mental gymnastics but i just had to trust what that code was telling me. Something is wrong in that relay circuit. How it had a break in the wire and corrosion like it did i have no idea.

Thanks for the feedback.

Maybe also do a stepped back overview pic or 2 of where that was?... that way someone else can look there on that same make/model truck if they are facing the same thing.