When SPN 3719 FMI 16 sets, the ECM is reporting an aftertreatment or emissions-system fault associated with the component named in this code.
SCR, NOx, temperature, pressure, catalyst, heater, wiring, and DEF-delivery faults use different diagnostic strategies, so diagnose the specific component rather than assuming a dosing problem.
When SPN 3719 FMI 16 sets, the ECM is reporting an aftertreatment or emissions-system fault associated with the component named in this code.
SCR, NOx, temperature, pressure, catalyst, heater, wiring, and DEF-delivery faults use different diagnostic strategies, so diagnose the specific component rather than assuming a dosing problem.
Exact thresholds and component layouts vary by OEM calibration.
Confirm whether the fault is ACTIVE and review companion codes and live data before replacing parts.
Modern aftertreatment systems use temperature sensors, NOx sensors, pressure sensors, heaters, catalysts, DEF equipment, and model-based ECM checks together.
The ECM compares sensor signals and expected system behavior. A fault can therefore be electrical, sensor-related, catalyst-related, mechanical, or caused by another upstream condition.
The diagnostic path should follow the component named by the code instead of assuming every SCR or NOx fault is a DEF dosing problem.
This is the classic “I’ve been idling all week and now it hates me” code. The truck needs a full regen, and it needs you to stop killing the regen halfway through.\n\nIf it comes back quickly, you’ve got a root cause (sensor data, exhaust leak, or restriction).
The DPF differential pressure sensor is usually mounted on/near the firewall or aftertreatment bracket. It connects to the exhaust via two small pressure tubes (pre- and post-DPF). Check the tubes for soot blockage, cracks, water intrusion, and heat damage.
Tip: Soot blockage or water in the DP tubes is a very common cause of erratic differential pressure readings.
If your tool can’t run actuator tests, you can still diagnose a lot with careful inspection + repeatability testing.
Critical aftertreatment faults can trigger rapid derate or inducement depending on OEM calibration and companion faults.
Exact behavior depends on ECM calibration and which companion faults are active.
If the fault repeats after clearing, diagnose it as ACTIVE and review companion codes and live data before replacing parts.
The videos below are embedded using YouTube’s official player. We do not host or claim ownership of this content. Use it as a visual reference and always confirm with diagnostics for your exact truck configuration.
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