Cummins fault code 6517
SCR Catalyst Conversion Efficiency: reading below normal (least severe)
What it means
Cummins' description: Aftertreatment SCR Catalyst Conversion Efficiency - Data Valid But Below Normal Operating Range - Moderately Severe Level.
SPN 4364 is Aftertreatment 1 SCR Conversion Efficiency. FMI 17 means the value is somewhat below normal. It's the mildest 'low' level, often an early warning.
The SCR (selective catalytic reduction) catalyst uses DEF to turn NOx into nitrogen and water. The ECM compares NOx before and after the catalyst to judge how well it's working. If it isn't, EPA rules require the engine to warn the driver and then derate.
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 one-time code with no lamp, or the amber lamp clears after a few drive cycles and fresh DEF.
Schedule a repair
Amber lamp with SCR efficiency or NOx codes that keep returning. Schedule diagnosis. These usually get worse, and inducement timers can be running in the background.
Stop and get help
Blinking lamp, inducement countdown, or the engine is already derated to low power or 5 mph. Stop and get it diagnosed. Clearing codes alone won't reset a real inducement.
Common causes
The sensor reading itself is out of range or the condition is real, so look at the system:
- Bad or diluted DEF, or not enough DEF being dosed
- Crystallized or clogged DEF doser
- Failing NOx sensor (very common)
- SCR catalyst contaminated by oil or fuel, or worn out
- Exhaust leak ahead of the sensors
- Upstream engine problem raising NOx: EGR fault, boost leak
What you can check before calling
- Check DEF level and quality first. It's the cheapest fix
- Look for exhaust leaks or soot tracks at clamps ahead of the catalyst
- Write down any countdown or derate message on the dash before it changes
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
Related SCR catalyst and inducement codes
- 6569 SPN 4363 FMI 3
SCR Outlet Temperature Sensor Circuit: circuit voltage high / shorted high - 6571 SPN 4363 FMI 4
SCR Outlet Temperature Sensor Circuit: circuit voltage low / shorted low - 6597 SPN 6928 FMI 31
SCR System Cleaning Inhibited Due to System Timeout: condition exists - 6634 SPN 7848 FMI 14
SCR System Conditions Not Met for Active Cleaning: special instructions - 5654 SPN 6881 FMI 13
SCR Operator Inducement Override Switch: out of calibration - 5653 SPN 6881 FMI 9
SCR Operator Inducement Override Switch: abnormal update rate
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 6517 mean?
Cummins fault code 6517 is J1939 SPN 4364 FMI 17: Aftertreatment SCR Catalyst Conversion Efficiency - Data Valid But Below Normal Operating Range - Moderately Severe Level. In plain terms: scr catalyst conversion efficiency: reading below normal (least severe).
Can I keep driving with Cummins code 6517?
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 6517?
SPN 4364 identifies the part or system (Aftertreatment 1 SCR Conversion Efficiency). FMI 17 describes the type of failure: reading below normal (least severe).
What usually causes Cummins code 6517?
The most common causes are: bad or diluted DEF, or not enough DEF being dosed; crystallized or clogged DEF doser; failing NOx sensor (very common).
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.