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Major Cummins NOx Sensor Issues and Fault Codes

Updated: Jul 8

NOX sensors are installed upstream and downstream of the SCR system to measure the conversion efficiency of NOX to N2. This measured value is a key input to control algorithms that command the injection rate of urea-water solution at each instant of time, as engine conditions dynamically vary in response to the driver’s commands of throttle position and gearing. Sensor errors lead to DEF injection rate being higher or lower than intended. A higher than intended rate can lead to ammonia emissions, which irritate the lungs. A lower than intended rate can lead to excessive NOX emissions and their subsequent health effects. As a preventative measure, regulatory agencies require on-board diagnostics that nearly continuously monitor conversion efficiency.

Should these diagnostics detect a problem with either sensor, the driver is alerted through a lamp on the dashboard and fault codes are recorded in the engine’s electronic control module. To encourage replacement of the faulty sensor, some regulators require than the engine’s power be reduced. The bus or truck journey is terminated, in some cases nearly immediately. Costs associated with unexpected repairs, lost revenue due to interrupted operation, it is great benefit of fleets to identify the failure efficiently and get the parts replaced quickly.

Below we list some of the most popular faulty code related to Cummins NOx sensor. This ‘random event’ failure can be sensitive to ambient humidity and exhaust gas temperature shortly after the engine is started. Sensor life for ‘wear out’ failures would be expected to be functions of the age of the sensor, the duty cycle to which the sensor is exposed, and noise factors such as ambient conditions and installation differences between different truck and bus models.

Cummins Fault Code ( NOx Sensor)


1694 3226 2 "Aftertreatment 1 Outlet NOx Sensor - Data erratic, intermittent or incorrect"

1885 3216 4 "Aftertreatment 1 Intake NOx Sensor Circuit - Voltage below normal, or shorted to low source"

1887 3226 4 "Aftertreatment 1 Outlet NOx Sensor Circuit - Voltage below normal, or shorted to low source"

2771 3226 9 Aftertreatment 1 Outlet NOx Sensor - Abnormal update rate

3228 3216 2 "Aftertreatment 1 Intake NOx Sensor - Data erratic, intermittent or incorrect"

3232 3216 9 Aftertreatment 1 Intake NOx Sensor - Abnormal update rate

3535 1213 9 Malfunction Indicator Lamp - Abnormal update rate NOx limits exceeded due to Insufficient

3545 3226 10 Aftertreatment 1 Outlet NOx Sensor - Abnormal rate of change

3583 5031 10 "Aftertreatment 1 Outlet NOx Sensor Heater - Abnormal rate of change"

3649 5024 10 "Aftertreatment 1 Intake NOx Sensor Heater - Abnormal rate of change"

3545 3226 10 Aftertreatment 1 Outlet NOx Sensor - Abnormal rate of change

3583 5031 10 "Aftertreatment 1 Outlet NOx Sensor Heater - Abnormal rate of change"

3649 5024 10 "Aftertreatment 1 Intake NOx Sensor Heater - Abnormal rate of change"

3681 3228 2 "Aftertreatment 1 Outlet NOx Sensor Power Supply – Data erratic, intermittent or incorrect"

3682 3218 2 "Aftertreatment 1 Intake NOx Sensor Power Supply – Data erratic, intermittent or incorrect"

3717 3226 13 "Aftertreatment 1 Outlet NOx Sensor - Out of Calibration"

3718 3216 13 Aftertreatment 1 Intake NOx - Out of Calibration

3725 3216 10 Aftertreatment 1 Intake NOx Sensor - Abnormal rate of change

3748 3216 20 "Aftertreatment 1 Intake NOx Sensor - Data not Rational - Drifted High"

3749 3226 20 "Aftertreatment 1 Outlet NOx Sensor - Data not Rational - Drifted High"

3988 3265 9 Aftertreatment 2 Outlet NOx - Abnormal Update Rate

4145 3255 9 Aftertreatment 2 Intake NOx Sensor - Abnormal update rate

4452 520668 31 "Aftertreatment 1 Outlet NOx Sensor Closed Loop Operation - Condition Exists"

6458 3216 20 "Aftertreatment 1 Intake NOx Sensor - Data not Rational - Drifted High"

6459 3216 21 "Aftertreatment 1 Intake NOx Sensor - Data not Rational - Drifted High"

6462 3226 20 "Aftertreatment 1 Outlet NOx Sensor - Data not Rational - Drifted High"

6463 3226 21 "Aftertreatment 1 Outlet NOx Sensor - Data not Rational - Drifted High"

6464 3226 2 "Aftertreatment 1 Outlet NOx Sensor - Data Erratic, Intermittent, or Incorrect."

6521 3226 4 "Aftertreatment Outlet NOx Sensor Circuit- Voltage below normal or shorted to low source"

6565 3226 10 Aftertreatment 1 Outlet NOx Sensor - Abnormal rate of change

6581 5031 10 "Aftertreatment 1 Outlet NOx Sensor Heater - Abnormal rate of change"

6621 3216 10 Aftertreatment 1 Intake NOx Sensor - Abnormal rate of change

We have over faulty 500 codes saved in our knowledge base regarding the NOx sensor. You are welcome to contact us if you need further details.


Source” Cummins.com




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