What is XCMG XE750D Fault Code E1370 (2) SPN5392 FMI31?

Fault Code E1370 (SPN5392 FMI31) indicates a "Condition Exists" error with the Diesel Exhaust Fluid (DEF) Quality Sensor circuit on the XCMG XE750D excavator. This code is part of the Selective Catalytic Reduction (SCR) aftertreatment system, which monitors the purity and concentration of the DEF solution used to reduce NOx emissions.

SPN5392 specifically refers to the DEF quality sensor, while FMI31 signals that a condition exists where the sensor has detected abnormal DEF quality, contamination, or dilution. For the XE750D's Tier 4 Final/Stage V compliant engine, this system is critical—prolonged operation with this fault can trigger engine derate modes or prevent the machine from starting after shutdown, severely impacting productivity on job sites.

Common Symptoms

When Code E1370 is active on your XCMG XE750D, operators typically experience:

• DEF/SCR warning lamp illuminated on the instrument cluster (amber or red)
• Engine power deration (reduced horsepower by 25-40%) after a grace period
• Frequent DEF system fault messages displayed on the monitor
• Increased diesel exhaust opacity or black smoke during operation
• Engine shutdown prevention after the machine is turned off (inducement mode)

Potential Causes

This fault code commonly appears due to several factors, especially in used excavators:

• Contaminated or diluted DEF fluid (most common—water intrusion, expired DEF, or incorrect fluid added)
• Failed DEF quality sensor due to crystallization buildup or internal element degradation
• Corroded electrical connectors at the DEF tank sensor harness (common on machines operating in wet/muddy conditions)
• Damaged wiring harness from rubbing against the DEF tank mounting brackets or frame rails
• DEF tank heater malfunction causing improper fluid temperature readings
• ECM software calibration issues requiring updated programming

How to Troubleshoot and Fix Code E1370 (2) SPN5392 FMI31

Step 1: Verify DEF Fluid Quality Drain a sample of DEF from the tank into a clean container. Check for discoloration, sediment, or unusual odor. DEF should be clear and colorless. If contaminated, completely drain and flush the DEF tank, then refill with fresh ISO 22241-compliant DEF fluid.

Step 2: Inspect the DEF Quality Sensor Located inside the DEF tank, remove the sensor assembly and inspect for crystallization buildup around the probe. Clean gently with distilled water—never use scrapers or abrasives. Check the sensor connector for corrosion or moisture intrusion, common on used XE750D models.

Step 3: Perform Electrical Diagnostics Using a multimeter, check sensor resistance (typically 1000-3000 ohms at 20°C, consult XCMG service manual for exact specs). Inspect the wiring harness from the sensor to the ECM, particularly where it routes near the DEF tank mounting points—a known rub-through location on older units.

Step 4: Check with Diagnostic Software Connect XCMG diagnostic software or compatible J1939 scan tool to monitor live DEF quality sensor voltage (should read 0.5-4.5V). If readings are erratic or out of range despite good connections, replace the sensor.

Step 5: Clear Codes and Test After repairs, clear fault codes, perform a SCR system reset through diagnostic software, and run the machine under load for 20-30 minutes to verify the fix.

Disclaimer: This guide provides general troubleshooting information. Always consult the XCMG XE750D service manual and consider professional diagnostic assistance for complex electrical or emissions system issues. Improper DEF system repairs may violate emissions regulations.