CM850 Electronic Control System – FAULT CODE 2771

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Overview

Circuit: Aftertreatment Outlet NOx Sensor Circuit SMALL | MEDIUM | LARGE

Circuit Description

The aftertreatment outlet nitrogen oxides (NOx) sensor is a smart device and receives commands from the engine electronic control module (ECM) via the J1939 datalink. The aftertreatment outlet NOx sensor receives power and a ground directly from the battery. The aftertreatment outlet NOx sensor performs its own internal diagnostics and reports malfunctions back to the primary engine ECM using the J1939 datalink. The aftertreatment outlet NOx sensor is permanently attached to the NOx control module. The aftertreatment outlet NOx sensor is used to measure the outlet NOx emissions from the engine.

Component Location

The aftertreatment outlet NOx sensor location can vary depending on engine application. It is usually located in the exhaust system at the outlet of the aftertreatment catalyst.

Shop Talk

On-Board Diagnostics (OBD) Information (Euro 4 Stage 1+ Certified Engines):

• The ECM illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
• An engine torque derate will be activated after 50 hours of engine operation with the fault code active.
• The ECM turns OFF the malfunction indicator lamp (MIL) after 1 ignition cycle that the diagnostic runs and does not fail. The MIL lamp can not be cleared using the INSITE™ electronic service tool.
• The fault code will be cleared from memory after 400 days or 9600 hours of engine operation.

The NOx sensor is permanently attached to the NOx control module. They are serviced as a single component and can not be replaced individually.

Possible causes of this fault code include:

• The aftertreatment outlet NOx sensor is not receiving power from the battery supply circuit in the OEM harness. This could be caused by an open circuit in the power supply wire, blown NOx sensor fuse, or low voltage supplied by the battery.
• Open return circuit on the aftertreatment outlet NOx sensor circuit between the battery circuit aftertreatment outlet NOx sensor.
• Open or short circuit on the J1939 datalink circuit between the engine ECM and aftertreatment outlet NOx sensor.
• Intermittent communications between the aftertreatment outlet NOx sensor and the primary engine ECM on the J1939 datalink.
• A damaged engine ECM
• Incorrect engine calibration.

Refer to Troubleshooting Fault Code t05-2771