How to Reset the DEF Level Sensor on a Paccar MX-13

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

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