What is XCMG XE750D Fault Code 3111-5 SPN4355 FMI5?

Fault Code 3111-5 (SPN 4355 FMI 5) indicates a Current Below Normal or Open Circuit condition in the Diesel Exhaust Fluid (DEF) Doser Inlet Pressure Sensor circuit. This fault is part of the Selective Catalytic Reduction (SCR) system that controls emissions on the XCMG XE750D excavator.

SPN 4355 specifically monitors the DEF doser inlet pressure, which measures the pressure of diesel exhaust fluid before it enters the dosing injector. FMI 5 signifies that the Engine Control Module (ECM) is detecting lower-than-expected current flow through the sensor circuit, typically indicating an open circuit, damaged wiring, or sensor failure. This fault is critical because the SCR system must maintain proper DEF pressure to meet emissions standards. Without accurate pressure readings, the ECM may trigger engine derate or prevent the machine from starting after shutdown, significantly impacting productivity on job sites.

Common Symptoms

When fault code 3111-5 is active on your XE750D, you may experience:

• DEF/SCR warning lamp illuminated on the instrument cluster (amber or red depending on severity)
• Engine power derate after a grace period, reducing machine performance by 25-40%
• Operator display message indicating SCR system malfunction or DEF pressure fault
• Engine may not restart after shutdown if fault persists beyond compliance countdown
• Increased fuel consumption due to ECM operating in failsafe mode with altered injection timing

Potential Causes

The most common technical causes for this fault code on used XCMG excavators include:

• DEF doser inlet pressure sensor failure due to crystallized urea contamination or internal sensor element degradation
• Damaged or corroded wiring harness between the sensor and ECM, particularly at connection points near the exhaust system where heat cycling causes connector pin corrosion
• Broken or frayed sensor wires at known rub points along the chassis rail where harness routing contacts frame members
• Faulty ECM connector pins (specifically the sensor supply voltage and ground circuits)
• Poor electrical ground connection at the sensor mounting location due to rust accumulation on used machines
• Water intrusion into sensor connector from pressure washing or environmental exposure

How to Troubleshoot and Fix Code 3111-5 SPN4355 FMI5

Step 1: Visual Inspection Begin by locating the DEF doser inlet pressure sensor on the SCR system (typically mounted on the DEF supply line near the dosing module). Inspect the sensor connector for corrosion, bent pins, or moisture. Check the wiring harness for visible damage, particularly where it routes near hot exhaust components or rubs against frame members—common wear points on used excavators.

Step 2: Electrical Testing Using a digital multimeter, perform these checks with the ignition off:

• Measure resistance between sensor connector pins (typically 2-pin connector): should read approximately 50-150 ohms (consult XCMG service manual for exact specification)
• Check supply voltage at the sensor connector with ignition on: should read approximately 5 volts from the ECM
• Test ground circuit continuity between sensor ground pin and chassis ground: should read less than 1 ohm

Step 3: Component and Harness Testing Disconnect the sensor and inspect for DEF crystallization around the sensor threads—a common issue on used machines with contaminated DEF. If electrical tests pass but fault persists, use XCMG diagnostic software (or compatible J1939 scan tool) to monitor live sensor data. Compare actual pressure readings against expected values during DEF system priming. For used excavators, carefully inspect harness routing and secure any loose sections that may have shifted over time, causing intermittent opens.

Step 4: Repair or Replace If sensor resistance is out of specification or no supply voltage is present, trace wiring back to the ECM connector checking for breaks. Replace damaged harness sections using proper gauge wire and weatherproof connectors. If the sensor itself has failed, replace with genuine XCMG parts to ensure proper calibration. After repairs, clear fault codes and perform a complete SCR system function test to verify proper DEF pressure readings.

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Disclaimer: This guide provides general troubleshooting information for educational purposes. Always consult the official XCMG service manual and qualified diesel technicians for your specific machine. Improper SCR system repairs may result in emissions non-compliance and further engine damage.