If your Paccar MX-13 is showing a DEF level warning even after refilling, chances are the DEF level sensor is stuck or out of sync. This is a common issue—and one that can lead to derate if ignored.

Here’s how to reset or recalibrate the DEF sensor using a diesel laptop.

🛠 What You’ll Need:

• Our Diesel laptop that supports Paccar engines

• RP1210 adapter (like Nexiq USB-Link 2 or 3)

• Truck parked with ignition on, engine off

🔄 Step-by-Step: Reset DEF Level Sensor on MX-13

1. Plug in your adapter and launch your diagnostic software

2. Connect to the MX-13 engine ECM

3. Go to Aftertreatment System > DEF Tank Level Sensor

4. Select “Relearn” or “Calibrate DEF Level Sensor”

5. Follow on-screen instructions:

   • Make sure DEF tank is at least ¾ full

   • Confirm no active DEF system faults

6. Click Start and let the recalibration process complete (2–5 minutes)

7. Power cycle the ignition and confirm warning is cleared

⚠️ If It Still Won’t Reset:

• Check for DEF contamination

• Inspect the DEF quality sensor

• Look for SPN 1761, SPN 3364, or SPN 5246 codes

• You may need to replace the tank module if the sensor fails calibration

💡 Pro Tip:

Many shops charge $300+ for this reset alone. A diesel laptop gives you that power anytime, anywhere—especially when paired with regen and code clearing capabilities.

👉 Need a Paccar-compatible scanner? Click here to shop diesel laptop kits