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Detroit Diesel SPN 520372 FMI 16 indicates that the Selective Catalytic Reduction (SCR) system efficiency is below the required threshold. This fault commonly appears when the aftertreatment system cannot properly reduce NOx emissions.
Symptoms
- Check engine light illuminated
- Aftertreatment warning
- DEF warning message
- Engine derate countdown
- Reduced engine power
Cause
This code is typically triggered by contaminated DEF, failed NOx sensors, clogged SCR catalyst, exhaust leaks, or wiring faults within the aftertreatment system.
Can You Keep Driving?
Driving may be possible temporarily, but continued operation can lead to progressive engine derate and speed limitation if not addressed.
Recommended Action
Inspect DEF quality and verify correct concentration. Check NOx sensors and wiring. If necessary, perform SCR efficiency diagnostics and inspect the catalyst for blockage or failure.
SPN 520372 FMI 16 indicates that SCR efficiency is below the required threshold, meaning the emissions system is not reducing NOx levels properly.
Common causes include contaminated DEF fluid, failed NOx sensors, clogged SCR catalyst, exhaust leaks, or improper DEF dosing.
Driving may be possible temporarily, but continued operation can result in progressive engine derate and speed limitation.
Yes. If the issue remains unresolved, the engine control module may progressively reduce vehicle speed to enforce emissions compliance.
Verify DEF quality, inspect NOx sensors and wiring, and perform SCR efficiency diagnostics to identify and repair the root cause.
Related Detroit Diesel Fault Codes
- Detroit Diesel SPN 5246 FMI 0 – Aftertreatment System Fault
- Detroit Diesel SPN 3364 FMI 2 – DEF Quality / Sensor Fault
- Detroit Diesel SPN 3719 FMI 0 – DPF Soot Level High
- Detroit Diesel SPN 520372 FMI 18 – SCR Efficiency Below Threshold Severe
Need Immediate Help With This Fault Code?
If your engine is derating, losing power, or unable to complete regeneration, don’t risk further damage or costly downtime.
Use 4RoadService to locate mobile truck repair, dealer diagnostics, or emergency roadside assistance near your location.
Important Notice
The information provided above is for general informational purposes only and should not replace official OEM service procedures. Always consult the manufacturer’s service manual or a qualified diesel technician before performing repairs. Operating a vehicle with active fault codes may result in further damage.