Symptoms of a Faulty NOx Sensor

1. ‌Check Engine Light (CEL) Illumination‌
   The most obvious sign is the activation of the ‌MIL (Malfunction Indicator Light)‌ or ‌SCR (Selective Catalytic Reduction) system warning light‌ on the dashboard. This occurs when the ECU detects abnormal NOx sensor signals‌12.

2. ‌Reduced Engine Performance‌

   • ‌Limp mode activation‌: The ECU may limit power to protect the engine, causing sluggish acceleration and reduced torque‌12.
   • ‌Poor throttle response‌: Delayed or inconsistent engine behavior due to incorrect air-fuel ratio adjustments‌2.

3. ‌Increased Fuel Consumption‌
   A faulty NOx sensor disrupts the ECU’s ability to optimize combustion, leading to ‌10-30% higher fuel consumption‌‌2.

4. ‌Failed Emissions Test‌

   • ‌Excessive NOx emissions‌: The sensor’s failure prevents proper SCR system operation, causing ‌50%+ higher NOx levels‌ than regulatory limits‌2.
   • ‌OBD-II error codes‌: Codes like ‌P2201-P2208‌ (NOx sensor circuit faults) or ‌P20C0‌ (NOx sensor performance) may appear‌13.

   • Diagnostic Methods

   • ‌OBD-II Scanner‌

     • Retrieve ‌specific NOx-related DTCs‌ (e.g., P2201, P2202) to confirm sensor issues‌13.
     • Monitor ‌live NOx data‌ (should fluctuate between 0-2000 ppm under normal conditions)‌3.

   • ‌Visual Inspection‌

     • Check for ‌physical damage‌ (cracks, corrosion) or ‌contamination‌ (soot, oil deposits) on the sensor probe‌3.
     • Verify ‌wiring integrity‌ (loose connections, frayed wires)‌3.

   • ‌Professional Testing‌

     • Use a ‌NOx analyzer‌ to measure tailpipe emissions.
     • Test ‌sensor voltage/resistance‌ (varies by model, typically 0.1-4.5V for signal output)‌3.

     • Key Notes

     • ‌Immediate action‌: Ignoring NOx sensor faults can ‌damage the SCR system‌ and ‌void emissions warranties‌‌2.
     • ‌Replacement cost‌: A new NOx sensor ranges from ‌$200-$800‌, depending on the vehicle model‌3.

     • For accurate diagnosis, consult a ‌certified technician‌ with access to ‌factory-grade diagnostic tools‌‌13.