Cummins Fault code 3226.4

Spn 3226 Fmi 4 equals Nox sensor circuit failed low. Says it's either a one off thing, reset and carry on, or if it's persistent then change the Nox sensor. Which you have done. If you didn't clear the codes after installing the new sensor, it should clear itself after three successful starts.

 

I was going to suggest maybe some bad wires to the sensor, but yes if the def isn't coming through, that will make the Nox reading go up. But I thought that would be a different code.

 

Double check your code and reconfirm the actual NOx sensor that you changed. There are two NOx sensors. They can be confused. The one on the engine itself, after the turbo is actually the "inlet" sensor. It gets confused all the time as being the outlet because it is after the turbo. The true outlet NOx sensor is after the DPF. The inlet and outlet NOx sensors are two completely different part numbers and not interchangeable even though they look identical and will plug into each others location. We have seen this many times, the wrong sensor got changed and the same code is active awards.

 

Did you confirm they installed the correct part number?