What is XCMG XE750D Fault Code 3110-6 SPN4354 FMI6?

Fault Code 3110-6 (SPN 4354 FMI 6) indicates a voltage issue with the Diesel Exhaust Fluid (DEF) Tank Level Sensor circuit—specifically, the system is detecting a voltage above the normal operating range or a short to positive voltage. This code is part of the J1939 diagnostic protocol used in modern diesel engines and affects the Selective Catalytic Reduction (SCR) aftertreatment system on the XCMG XE750D excavator.

SPN 4354 refers specifically to the DEF Tank Level Sensor, while FMI 6 designates a "voltage above normal or shorted high" condition. The Engine Control Module (ECM) continuously monitors the DEF level sensor circuit for proper voltage signals (typically 0.5-4.5V). When voltage exceeds threshold limits, this fault triggers.

This is critical for the XE750D because the SCR system requires accurate DEF level monitoring to maintain emissions compliance. Failure to address this code can result in engine derate or shutdown per EPA/Euro emissions regulations, severely impacting machine productivity.

Common Symptoms

• DEF level gauge reading 100% constantly or displaying erratic/frozen readings on the monitor
• Amber or red warning lamp illuminated on the instrument cluster related to aftertreatment system
• Engine derate notification appearing after a countdown period (typically 50-100 engine hours)
• Reduced engine power or limited maximum RPM if the fault persists beyond warning period
• Frequent DEF system-related alarms even after refilling the DEF tank

Potential Causes

The most common technical failures causing this high voltage fault on used XCMG excavators include:

• DEF tank level sensor internal failure causing short circuit to positive voltage (common after 5,000+ hours)
• Damaged or chafed wiring harness between the sensor and ECM, particularly at routing points near the fuel tank mounting brackets
• Corroded or moisture-contaminated connector pins at the sensor plug (DEF is hygroscopic and attracts moisture)
• Short circuit in the harness due to pinched wires during previous tank removal or maintenance
• ECM internal fault in the sensor supply circuit (rare, but possible in high-hour machines)
• Poor grounding connection at the DEF tank assembly causing voltage feedback

How to Troubleshoot and Fix Code 3110-6 SPN4354 FMI6

Step 1: Visual Inspection and Connector Check

Begin by accessing the DEF tank level sensor located on top of the DEF tank assembly. Disconnect the sensor connector and inspect for corrosion, bent pins, moisture intrusion, or crystallized DEF residue. On used excavators, this connector frequently shows corrosion due to DEF vapor exposure. Clean contacts with electrical contact cleaner and verify the connector seal integrity.

Step 2: Sensor Circuit Voltage Testing

With the sensor disconnected and ignition on (engine off), use a digital multimeter to measure voltage on the ECM supply wire at the harness side connector. You should read approximately 5 volts (reference voltage from ECM). If voltage reads significantly higher (7V+) or battery voltage (24V), there's a short to positive voltage in the harness—trace the wiring for damage.

Step 3: Sensor Resistance and Ground Testing

Measure resistance across the sensor terminals with the sensor disconnected. Compare readings against XCMG specifications (typically 50-350 ohms depending on temperature). An open circuit or infinite resistance indicates sensor failure. Also verify ground circuit continuity from the sensor ground pin to chassis ground—resistance should be less than 5 ohms.

Step 4: Harness Inspection for Used Equipment

On used XE750D excavators, physically trace the DEF sensor harness from tank to ECM. Pay special attention to areas where the harness passes near sharp edges, mounting brackets, or hydraulic lines. Look for wire insulation wear, exposed copper, or heat damage. Repair any damaged sections with proper gauge wire and heat-shrink connections.

Step 5: DEF Quality and Tank Condition

Verify DEF quality using a refractometer (should read 32.5% urea concentration). Contaminated or crystallized DEF can damage sensors. Inspect the DEF tank interior for sediment or contamination that might affect sensor operation.

Step 6: Component Replacement and Verification

If testing confirms sensor failure, replace with a genuine XCMG or OEM-equivalent DEF level sensor. After installation, clear fault codes using XCMG diagnostic software or a compatible J1939 scan tool. Run the engine and verify the DEF level reads correctly and the fault does not return.

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Disclaimer: This guide provides general diagnostic information for experienced technicians. Always consult the official XCMG XE750D service manual for model-specific procedures, torque specifications, and safety precautions. If you lack proper diagnostic tools or experience with high-voltage electrical systems, consult a certified XCMG technician or authorized service center.