Cummins fault code 6621
Intake NOx Sensor: abnormal rate of change
What it means
Cummins' description: Aftertreatment 1 Intake NOx Sensor - Abnormal rate of change.
SPN 3216 is Aftertreatment 1 Intake NOx. FMI 10 means the reading changed faster or slower than is physically possible, which points to a sensor or wiring problem, or a real sudden change.
NOx sensors sit in the exhaust before and after the SCR catalyst. They measure nitrogen oxides so the ECM can control DEF dosing and confirm emissions are under control. Each sensor has its own small control module and talks over the J1939 network.
What the lamp means
This code normally doesn't turn on a dash lamp. It's logged in the ECM for a technician to see, and often explains another active code.
Green, yellow, red: three ways this can look
The same code can be a quick fix or a reason to shut down. Match your situation to the closest example.
Keep an eye on it
A NOx code shows up once with no lamp, often during cold start or warm-up, and clears.
Schedule a repair
Amber lamp with a NOx sensor code that keeps coming back. It's typically a sensor replacement, and it should be done before it triggers SCR inducement.
Stop and get help
NOx codes alongside a derate or inducement countdown. Get it in now. The truck will keep losing power until the emissions system reads correctly.
Common causes
The sensor reading itself is out of range or the condition is real, so look at the system:
- Aging NOx sensor reading wrong
- Exhaust leak near the sensor
- Real high NOx from an EGR, DEF or SCR problem
- Sensor contaminated by oil or coolant
What you can check before calling
- Look for exhaust leaks or soot near the sensor locations
- Check the sensor connectors and that the sensor modules are mounted and dry
- Note whether other SCR or DEF codes are active at the same time
Clearing the code without fixing the cause usually brings it right back, and on emissions systems it can restart derate timers. For the bigger picture, read our guide: DEF warning lights and derate: what diesel drivers need to know.
Engines and sources
Listed by Cummins for: QSB 6.7, QSL 9, QSX 15, QSB 4.5, QSF 3.8 (With SCR), QSG 12. Cummins uses the same fault code numbers across its electronic engines, including on-highway models like the ISB/B6.7, ISL/L9 and ISX/X15, though not every code applies to every engine or software level. Source: Cummins Tier 4 Fault Codes. Always confirm with Cummins service information (QuickServe) for your engine serial number.
Same SPN, other failure types
- 1885 SPN 3216 FMI 4
Intake NOx Sensor Circuit: circuit voltage low / shorted low - 3228 SPN 3216 FMI 2
Intake NOx Sensor: erratic or intermittent signal - 3232 SPN 3216 FMI 9
Intake NOx Sensor: abnormal update rate - 3718 SPN 3216 FMI 13
Intake NOx: out of calibration - 3725 SPN 3216 FMI 10
Intake NOx Sensor: abnormal rate of change - 3748 SPN 3216 FMI 20
Intake NOx Sensor: data drifted high - 6458 SPN 3216 FMI 20
Intake NOx Sensor: data drifted high - 6459 SPN 3216 FMI 21
Intake NOx Sensor: data drifted low
Related NOx sensors codes
- 6582 SPN 3228 FMI 2
Outlet NOx Sensor Power Supply: erratic or intermittent signal - 6581 SPN 5031 FMI 10
Outlet NOx Sensor Heater: abnormal rate of change - 6565 SPN 3226 FMI 10
Outlet NOx Sensor: abnormal rate of change - 6521 SPN 3226 FMI 4
Outlet NOx Sensor Circuit- Voltage below normal or shorted to low source: circuit voltage low / shorted low - 6464 SPN 3226 FMI 2
Outlet NOx Sensor: erratic or intermittent signal - 6463 SPN 3226 FMI 21
Outlet NOx Sensor: data drifted low
Look up another code
Cummins fault code (like 1922), J1939 SPN and FMI (like SPN 3251 FMI 0), or an OBD-II code (like P0420).
Questions
What does Cummins fault code 6621 mean?
Cummins fault code 6621 is J1939 SPN 3216 FMI 10: Aftertreatment 1 Intake NOx Sensor - Abnormal rate of change. In plain terms: intake nox sensor: abnormal rate of change.
Can I keep driving with Cummins code 6621?
Usually, yes. This code doesn't normally turn on a lamp by itself, but check for other active codes that might be more serious. Look at the green, yellow and red examples on this page to judge your situation.
What is the SPN and FMI for Cummins code 6621?
SPN 3216 identifies the part or system (Aftertreatment 1 Intake NOx). FMI 10 describes the type of failure: abnormal rate of change.
What usually causes Cummins code 6621?
The most common causes are: aging NOx sensor reading wrong; exhaust leak near the sensor; real high NOx from an EGR, DEF or SCR problem.
Diesel down in the Midlands?
We work on Cummins-powered pickups, vans and medium-duty trucks across Lexington, Columbia and the Midlands, on site at your yard or roadside.