18432/P2000/008192

Possible Symptoms

• MIL (Malfunction Indicator Lamp) ON
• DTC stored in ECM
• Possible loss of power (limp mode)
• Increased NOx emissions
• Fuel economy concerns during regeneration cycles

Possible Causes

• NOx Catalyst efficiency below threshold
• Faulty or aging NOx Catalyst
• Faulty Oxygen Sensor 1 Before Catalytic Converter -GX10-
• Faulty Oxygen Sensor 1 After Catalytic Converter -GX7-
• Faulty or slow Exhaust Gas Temperature Sensor(s)
• Poor quality fuel or incorrect sulfur content
• Exhaust leaks upstream or around NOx Catalyst
• Adaptation values for O₂ sensors not realized
• Low reductant consumption or dosing malfunction

Monitoring Conditions

• Monitor Strategy: NOx Efficiency Below Threshold
• Malfunction Criteria:
  • O₂ signal post NOx Catalyst < 0.95
  • O₂ signal pre NOx Catalyst < 0.045
  • Mass of reductant consumption < 0.9 g
• Enable Conditions:
  • Regeneration demand for NOx Catalyst = ON
  • Adaptation of O₂ sensors pre and post NOx Catalyst = realized
  • Engine speed 1,000 – 2,750 RPM
  • Upstream turbine temp 50 – 850 °C
  • Temperature of upstream NOx Catalyst 220 – 550 °C
  • Engine coolant temp 40 – 105 °C
  • Fuel temp < 90 °C
  • Accelerator pedal position > 1.0 % and < 100.0 %
  • Engine run time > 240 s
  • Barometric pressure > 750 hPa
• Monitoring Time Length: 10.0 s
• MIL Illumination: 2 DCY

Possible Solutions

• Check Oxygen Sensor 1 Before Catalytic Converter -GX10-
• Check Oxygen Sensor 1 After Catalytic Converter -GX7-
• Check Exhaust Gas Temperature Sensors
• Inspect for exhaust leaks before and around NOx Catalyst
• Verify reductant (AdBlue®) dosing and consumption
• Check for correct fuel quality (low sulfur, per manufacturer spec)
• Replace faulty O₂ sensor(s) or EGT sensor(s) as necessary
• Replace NOx Catalyst if efficiency cannot be restored

Special Notes

• This fault indicates the ECM has determined that the NOx Catalyst is not reducing emissions efficiently enough under monitored conditions.
• Aged catalysts or sulfur-contaminated fuel are common causes.
• Always verify O₂ sensor functionality and exhaust tightness before replacing the NOx Catalyst.
• Repair information and test procedures vary by engine; always confirm with the official factory repair manual.