2021 Freightliner M2 - Cummins B6.7 - Fault Code P225D NOx Sensor Stuck

Question

Got a 2021 M2 with the Cummins 6.7. Fault code P225D11 is active: 'NOx Sensor 1/2 Stuck - High'. The truck runs fine, no derate yet, but the light is on and we need to pass inspection. I've tried clearing it with a generic tool but it comes back immediately after the second start cycle.

I checked the wiring to the downstream NOx sensor and everything looks intact. Is this just a bad sensor or could it be related to the DEF dosing? The truck only has 45,000 miles so it seems early for a sensor failure, but I know these are sensitive.

NightShiftNate · Accepted Answer

✅ Confirmed fix: This was actually a software logic issue addressed in a Cummins TSB. The ECM was too 'sensitive' to NOx sensor fluctuations during warm-up. I performed a calibration update (flash) to the latest revision using Cummins Insite, and the P225D code remained inactive. No parts were actually needed.

RamRunnerRay · Answer

P225D on the B6.7 is almost always the sensor itself. The internal ceramic element gets 'poisoned' by sulfur or just fails from thermal shock. Before replacing, verify you have 12V and ground at the sensor plug and about 2.5V on the CAN Hi/Lo lines. If power and data are there, the sensor is toast.

2021 Freightliner M2 - Cummins B6.7 - Fault Code P225D NOx Sensor Stuck

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