SPN 3364 FMI 9: DEF Quality Sensor - Abnormal Update Rate / Communication Lost (Cummins X15)

SPN 3364 FMI 9 - DEF Quality Sensor Communication Lost

**What This Means**: The ECM has lost communication with the DEF quality sensor via the J1939 data link [citation:6]. The DEF quality sensor is a smart device that communicates digitally - when communication fails, this code sets.

📍 Component Location

The DEF quality sensor is typically mounted **in the DEF tank** or **in-line with the DEF dosing unit supply line** [citation:6].

🔍 Diagnostic Steps

**Step 1: Visual Inspection**

• Check sensor connector for corrosion, bent pins, or water intrusion
• Inspect wiring harness for damage, chafing, or rodent damage

**Step 2: Power and Ground Tests**

• Key on, engine off
• Verify 12V power at sensor connector
• Check ground continuity (< 0.5 ohms)

**Step 3: CAN Bus Tests**

• Measure resistance between CAN High and CAN Low: **60 ohms** expected
• Measure voltage on CAN High: ~2.5-2.7V
• Measure voltage on CAN Low: ~2.3-2.5V

⚠️ Important Note

This fault code **cannot be cleared with INSITE** or standard diagnostic tools [citation:6]. It will clear automatically when the communication is restored - start the engine and let it idle for up to 5 minutes after repair [citation:6].