NOx Inlet or Outlet Sensor Failure (200K+ Mile Normal Wear)
The VOLVO-MACK-NOX-SENSOR-FAILURE (Volvo/Mack D/MP Series) diesel fault code means: NOx Inlet or Outlet Sensor Failure (200K+ Mile Normal Wear). This is a serious severity code.
- Keep driving?
- Yes, but fix soon
- DIY difficulty
- intermediate
- Estimated cost
- $400-$900
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Common Symptoms
- Amber Check Engine Light and SCR efficiency warning
- Progressive derate warning (55 mph then 5 mph)
- NOx reading frozen or stuck at a value
- Failed emissions test
- Increased or decreased DEF consumption
Probable Causes (Ranked by Likelihood)
- NOx sensor aged past typical service life (200-300K miles) Very Likely
- Contamination from DEF crystallization around sensor tip Likely
- Heat-damaged harness at sensor pigtail Possible
- SCR thermal event caused sensor damage Possible
- Connector corrosion Less Likely
Step-by-Step Diagnostic Procedure
Connect Volvo PTT or Mack Guided Diagnostics and read inlet/outlet NOx live values for plausibility; a frozen reading confirms sensor failure.
Inspect harness for heat damage or white urea crystallization at connector.
NOx sensors are $350-$500 each and come with integrated pigtail — sensor comes as an assembly.
Replace the offending sensor; if both are over 200K miles, replace both proactively.
After replacement, run the SCR self-test procedure via PTT or Guided Diagnostics and clear codes.
Verify the SCR conversion efficiency returns within spec after a warm-up cycle.
Frequently Asked Questions
What does Volvo/Mack code NOX-SENSOR-FAILURE mean?
Volvo/Mack code NOX-SENSOR-FAILURE (NOx Inlet or Outlet Sensor Failure (200K+ Mile Normal Wear)) is a serious-severity diagnostic trouble code set on D11/MP7, D13/MP8, and D16/MP10 diesel engines in Volvo VNL/VNR and Mack Anthem/Pinnacle/Granite/Titan trucks. It indicates a fault in the NOx sensor system and should be read with Volvo Premium Tech Tool (PTT) or Mack Guided Diagnostics.
Can I drive a Volvo or Mack truck with code NOX-SENSOR-FAILURE?
Short distances may be acceptable to reach a repair facility, but the fault will escalate to derate (typically 55 mph then 5 mph on aftertreatment faults). Do not defer diagnosis beyond a shift.
How much does it cost to fix Volvo/Mack code NOX-SENSOR-FAILURE?
Typical repair falls in the range $400-$900. Sensor/wiring repairs are at the low end; EGR cooler, NOx sensor set, DEF pump, injector, or head work runs at the high end. Volvo PTT or Mack Guided Diagnostics is normally required for calibration and parameter programming.