If your truck is stuck in derate and flashing the dreaded SPN 5246 FMI 0 or SPN 5246 FMI 15, it’s usually related to your aftertreatment system—most often the result of a failed regen, DEF quality issue, or a sensor problem.

Here’s how to clear SPN 5246 using a diesel laptop and get your truck back on the road.

🛠 What You’ll Need:

• A diesel laptop diagnostic kit

🔄 Step-by-Step: Clear SPN 5246

1. Connect your adapter to the truck and launch your diagnostic software

2. Establish connection with the ECM

3. Check for additional codes (common companion faults: SPN 3364, SPN 3058, SPN 4334)

4. If regen was recently interrupted, attempt to run a parked regen

5. Once soot level and temp are normal, go to the fault code list

6. Select SPN 5246 and click “Clear Code” or “Reset Aftertreatment System”

⚠️ Still Won’t Clear?

• Make sure all sensors (DEF level, NOx, temp) are functioning

• Check that there are no DEF quality or dosing errors

• Ensure no blocked lines or frozen DEF

• A failed component (e.g. NOx sensor or DEF module) may require replacement before the code will clear

💡 Pro Tip:

SPN 5246 is a protective code—not always the root issue. You’ll often need to fix the underlying problem before clearing it.

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