If you're a trucker or shop owner, you've probably seen codes like SPN 3719 or SPN 5246 pop up on a scan tool or dash. These codes are more than just warnings—they’re signals your truck is about to enter derate, regen, or even shut down if ignored.
Here’s a breakdown of the most common SPN codes and what to do when you see them.
🔧 What Is an SPN Code?
SPN stands for Suspect Parameter Number. It tells you which system or component is triggering the fault. Combined with an FMI (Failure Mode Indicator), you get a full picture of what’s wrong.
🚨 Top 5 SPN Codes Every Diesel Operator Should Know
1. SPN 5246 FMI 0 – Aftertreatment Derate Active
This code usually appears when a regen has failed or been skipped. It means your truck is headed for a 5 MPH derate unless you clear the fault and complete a successful regen.
2. SPN 3719 FMI 16 – DPF Soot Load Too High
Indicates your Diesel Particulate Filter (DPF) is full. You’ll need to perform a forced regen to prevent a shutdown.
3. SPN 4364 FMI 18 – NOx Sensor Performance
A failed NOx sensor affects emissions and can trigger a derate. If left unresolved, it can also impact fuel economy.
4. SPN 102 FMI 18 – Mass Air Flow Too Low
Often related to dirty sensors, clogged intake, or turbo issues. This one can trigger limp mode if airflow doesn’t improve.
5. SPN 132 FMI 31 – EGR Valve Malfunction
Common in trucks with lots of idle time. A stuck or failing EGR valve can create cascading emissions problems.
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Clear inactive or resolved faults
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Perform forced regens
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Test sensors and reset parameters
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Avoid dealer visits, downtime, and tow bills
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