Case IH 2771 – Engine Control Module (ECM): Aftertreatment 1 Outlet Nitrogen Oxide (NOx) Sensor Update Rate Abnormal

Indicates a communication failure or an invalid data transfer rate on the J1939 data link between the Engine Control Module (ECM) and the SCR Outlet NOx sensor. This will often trigger an amber warning light, a check engine light, and can result in an engine protection torque derate (limp mode).

• VESTRUM CVX
• Steiger series
• Magnum series

1. 1

   Use an electronic service tool (like Cummins INSITE or Case IH EST) to confirm Code 2771 / SPN 3226 FMI 9 is active.

2. 2

   Visually inspect the passenger-side/exhaust aftertreatment wiring harness. Look for melted wires, chafing, or false contacts that could cause a ground issue.

3. 3

   Disconnect the NOx sensor and inspect the connector for damaged pins, corrosion, or moisture.

4. 4

   Ensure the termination resistance on the J1939 data link is within the specified range of 54 - 66 Ω to rule out data corruption.

5. 5

   Verify that the sensor is receiving proper battery voltage. If the voltage is below 11 VDC (on a 12V system), troubleshoot the power supply circuit.

1. 1

   Power Down

   Turn the keyswitch off and disconnect the batteries to prevent electrical shorts during repair.

2. 2

   Harness Repair (If Applicable)

   If the diagnostic checks revealed a melted or damaged sensor harness, repair or replace the harness section before replacing the sensor.

3. 3

   Remove the Old Sensor

   Locate the SCR Outlet NOx sensor near the exhaust stack/DPF unit. Use a 22mm O2 sensor socket and a 3/8 drive ratchet to remove the sensor. (A torch may be required if the sensor is seized in the exhaust pipe).

4. 4

   Install the New Sensor

   Thread the new NOx sensor into the exhaust outlet and tighten to OEM torque specifications. Route the wiring safely away from extreme heat sources and plug it into the harness.

5. 5

   Restore Power

   Reconnect the batteries.

6. 6

   Verify Repair

   Connect your electronic service tool and clear the inactive fault codes. Perform a parked regeneration to verify the repair and ensure the SCR system is reading NOx conversion correctly.