SPN 4364 FMI 18?

[JMBT]

Jimeneztrans84, also check the simple stuff. Mine has thrown this code often since new. It can be, and I would say is often, set by poor quality DEF fluid. If you have no other codes. I would first check for leaks, use the DEF pressurizing test on insite, then get under and look for leaks. Then replace the DEF pump filter if it has been in longer then 50K. Then unplug both NOX sensors and reseat them with a little di-electric grease. Then clear the code. If it comes back, which mine never has after the above, then pull and inspect the decomposition tube for deposits, and look into replacing the nox sensor or sensors.
4364 18 is such a BS code quickserve even says "do not replace parts because of it unless other codes are present"
If connected to insite during a regen and both sensors are reading stable, I would leave them be. When one goes bad it will usually throw its own code. I have replaced the in 3 times and the out twice in 600K.