Circuit DescriptionThe aftertreatment SCR intermediate NH3 (ammonia) sensor is a smart device that communicates with the engine control module via the J1939 data link. The aftertreatment intermediate NH3 sensor performs its own internal diagnostics and reports malfunctions back to the primary engine control module using the J1939 data link. The aftertreatment intermediate NH3 sensor is used to measure the ammonia in the aftertreatment system.

Component LocationThe aftertreatment SCR intermediate NH3 sensor is located in the middle of the aftetreatment SCR catalyst.

Conditions for Running the DiagnosticsThis diagnostic runs when the aftertreatment SCR intermediate temperature has been above 170 C [338 F] for a calibratible period of time while the engine is running.

Conditions for Setting the Fault CodesThe aftertreatment SCR intermediate NH3 sensor reported the resistance of the trim resistor is out of range.

Action Taken When the Fault Code is ActiveThe ECM illuminates the amber CHECK ENGINE lamp and/or the Malfunction Indicator Lamp (MIL) immediately when the diagnostic runs and fails.Diesel exhaust fluid injection into the aftertreatment system is disabled.Engine torque will be reduced if the engine is operated for an extended period of time with this fault active.Conditions for Clearing the Fault CodeTo validate the repair, start and operate the engine to raise exhaust temperatures. This can be done by either driving the vehicle or initiating a stationary regeneration using INSITE™ electronic service tool.The aftertreatment SCR intermediate temperature must be above 170 C [338 F] for 5 seconds before the aftertreatment SCR intermediate NH3 sensor can run its internal diagnostics.

The fault code status displayed by INSITE™ electronic service tool will change to INACTIVE immediately after the diagnostic runs and passes.The ECM will turn off the amber CHECK ENGINE lamp immediately after the diagnostic runs and passes.For On-Board Diagnostics (OBD) engines, the ECM will extinguish the Malfunction Indicator Lamp (MIL) after three consecutive trips where the diagnostic runs and passes.The Reset All Faults command in INSITE™ electronic service tool can be used to clear active and inactive faults, as well as extinguish the MIL for OBD applications.

Shop TalkPossible causes of this fault code include:

A malfunctioning aftertreatment SCR intermediate NH3 sensor probeA malfunctioning aftertreatment SCR intermediate NH3 sensor module

Possible Cause:1) NH3 sensor probe failure2) ECM calibration