2018 Freightliner Cascadia SPN 3216 FMI 9 - SCR NOx Inlet Sensor Data Erratic

Question

My DD15 is stuck in a 5 MPH derate and I keep getting a code for the inlet NOx sensor. The dashboard shows an SCR failure warning and I cannot initiate a parked regen to clear the countdown timer. I checked the connector at the sensor and it looks clean but the code keeps coming back as active immediately after clearing.

Dave Kowalski · Accepted Answer

Solution was a failed NOx Inlet Sensor (Part # A0101532228). I replaced the sensor and found a chafed wire in the overlay harness about 6 inches back from the connector. After repairing the wire and installing the new sensor, I used DiagnosticLink 8.0 to perform the SCR Low Temp Burn-off which cleared the 5 MPH derate and allowed the SCR inducements to reset. Total cost was about $580 for the sensor and two hours of labor.

Marcus Bell · Answer

You need to check the resistance of the CAN lines at the sensor plug. Pin 3 and 4 should show roughly 60 ohms with the batteries disconnected; if it's 120 or 0, you have a harness break or a short in the frame rail loom.

backyard_bart · Answer

If you are in a derate, a simple sensor swap won't fix it. You will need DiagnosticLink software to perform an SCR Efficiency Test and a 'Reset DEF Derate' command once the new hardware is detected.

torque_terry · Answer

Before replacing the sensor, check the Power Distribution Center (PDC) fuses for the Aftertreatment Control Module. If the ACM isn't getting clean power, it will drop the CAN link to the NOx sensors first.

2018 Freightliner Cascadia SPN 3216 FMI 9 - SCR NOx Inlet Sensor Data Erratic

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