Fault codes SPN 3720 FMI 0 and FMI 15 warn that the Diesel Particulate Filter ash load has reached or exceeded acceptable limits. These codes don’t affect performance immediately—but if ignored, they can lead to regen failures or require DPF replacement.

What Do These Codes Mean?

• SPN 3720 = Aftertreatment 1 DPF Ash Load %

• FMI 0 = Data valid, above normal range (most severe)

• FMI 15 = Data valid, above normal but least severe level

FMI 0 signals a more urgent condition, while FMI 15 is informational. Both indicate it’s time to service or replace the DPF.

Symptoms & Impact

• Maintenance light illuminates at key-on

• No immediate engine derate or performance loss

• Will not self-clear without DPF service and reset

• If left unchecked, may lead to regeneration failure or catalyst damage

Common Causes of SPN 3720

• DPF has exceeded its service life with excessive ash

• Differential pressure sensor is triggering the ash load alert

• Ash counter not reset after DPF cleaning or replacement

🔧 How to Diagnose & Resolve

1. Connect your diesel laptop and identify SPN 3720 FMI 0 or 15.

2. Confirm DPF ash percentage via live data or ECM parameters.

3. If ash is too high: clean or replace the DPF (OEM or certified cleaner).

4. Run the “Aftertreatment Maintenance Filter Installation” reset using your tool:

   • Cummins Insite or Diesel Tech

5. Turn the key off for ~100 seconds, then restart to confirm the code clears.

Tool Required

• Diesel laptop

Quick Pro Tip

SPN 3720 FMI 15 often appears as a mileage-based reminder rather than a failure—so it isn't urgent immediately. Fix within a few weeks to avoid regen issues. FMI 0 is more pressing and needs faster action

Final Takeaway

Codes SPN 3720 FMI 0/15 indicate your DPF’s ash capacity is maxed or near max. It’s informational—but it demands preventive maintenance. Service the filter, perform the ash counter reset, and use your diesel laptop to confirm the code is permanently cleared.