Hunter013
Senior Member
2015 Peterbilt 567 with ISX15. Truck came back one day saying its DPF was full. I was able to regen it and run it one more day while I was looking for options on a DPF and DOC. Then it came back with a derate code of 2976 DEF dosing unit temp - data erratic. We checked harness and volts. Everything ohmed out and took a load test successfully, and volts were within spec. I put on a new DEF dosing unit and codes 3559 DEF dosing unit supply low and 3558 DEF dosing unit supply high popped on. I checked voltage and everything was within spec. I put the original DEF dosing unit back on and then it would go between 3558 and 3559 being active separately and together randomly. We ended up taking out all the harnesses and inspecting them and didn't find anything. Now when we initially check codes with engine off, the following codes are active: 1921, 3559, 2976, 3135, 1879, 3133. When we start it and it runs for a minute, only 1921, 3135 and 2976 come active. I hate to say the ECM internally failed without a better diagnosis first. What else can I check?