Aftertreatment 1 Outlet NOx Sensor - Abnormal Update Rate
The CUMMINS-2771 (Cummins) diesel fault code means: Aftertreatment 1 Outlet NOx Sensor - Abnormal Update Rate. This is a moderate severity code.
- Keep driving?
- Yes, but fix soon
- DIY difficulty
- advanced
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What Are the Symptoms of CUMMINS-2771?
- Amber Check Engine lamp
- Often logged together with other aftertreatment, DEF or SCR faults
- SCR dosing may be limited while the outlet NOx reading is missing
What Causes CUMMINS-2771? (Most Likely First)
- Outlet NOx sensor module not sending its J1939 message at the expected rate: lost power, ground or CAN connection to the sensor High
- ECM battery feed or ground connector with damaged, bent or corroded pins (Navistar found connectors 1027, 9253 and 9260 behind clusters of these faults on 2013 ProStar/LoneStar/TranStar/9900i) High
- Failed outlet NOx sensor module Medium
Can I Still Drive with CUMMINS-2771?
Yes, but fix soon. CUMMINS-2771 is rated moderate severity. It is not an immediate stop-driving fault, but it will not clear itself — book the repair rather than ignoring it.
Frequently Asked Questions
What does Cummins fault code 2771 mean?
Fault code 2771 means Aftertreatment 1 Outlet NOx Sensor - Abnormal Update Rate (SPN 3226 FMI 9): the NOx sensor after the SCR catalyst is not updating its reading on the J1939 network as often as the engine ECM expects. It is an amber-lamp fault.
Is 2771 a Cummins-specific code?
The number 2771 is Cummins' own fault code; the underlying fault is the J1939 pair SPN 3226 FMI 9, which any tool reading the engine ECM will also show. The description here is the one Navistar prints for the 2013 Cummins ISX15 in its International trucks.
Mechanics Guide Step-by-step diagnosis
How Do You Diagnose CUMMINS-2771?
Read all active codes. If three or more aftertreatment, DEF or SCR update-rate faults are active at once, Navistar's procedure is to inspect the ECM power and ground connectors before touching any sensor.
Check the battery-box connectors for the ECM positive and negative feeds for corrosion, bent pins and seating; repair per the wire-repair procedure and reseat.
With power and grounds proven, check the outlet NOx sensor's own power, ground and CAN wiring at the sensor connector.
Only then replace the outlet NOx sensor module if it still fails to report.
Sources 2
This page is built from documented references. Verify against your own service info before repair work.
- Navistar iKNow article IK0800426 "Cummins ISX 15L with Multiple ECM Faults" (rev. 2, June 2014, filed with NHTSA)fault table for 2013 LoneStar, ProStar, TranStar and 9900i with the Cummins ISX15: SPN 3226 / FMI 9 / Cummins FC 2771 / amber lamp / "Aftertreatment 1 Outlet NOx Sensor - Abnormal Update Rate"; names the ECM battery-feed and ground connectors as the common cause when several such faults are active together.
- SAE J1939-73Application Layer: Diagnostics (defines the SPN/FMI fault-identifier framework)
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