What is XCMG XE750D Fault Code 1627-5 SPN931 FMI5?

Fault Code 1627-5 (SPN 931 FMI 5) indicates a Coolant Level Sensor Circuit Current Below Normal or Open Circuit condition in the XCMG XE750D excavator's engine management system. This code is triggered when the Engine Control Module (ECM) detects abnormally low current or an open circuit in the coolant level sensor wiring, preventing accurate monitoring of engine coolant levels.

This fault is critical for the XE750D's diesel engine protection system. Without reliable coolant level data, the ECM cannot properly safeguard against overheating, potentially leading to catastrophic engine damage. The coolant level sensor acts as a first-line defense, alerting operators before temperature sensors detect actual overheating. On used excavators, this code often appears due to age-related wiring degradation rather than actual coolant loss.

Common Symptoms

• Coolant level warning light illuminated on the instrument cluster, even when coolant reservoir appears full
• Engine derate mode activated, limiting machine to reduced power output (typically 50-70% capacity)
• Intermittent or persistent alarm sounds from the cab warning system
• Diagnostic display showing error code 1627-5 or SPN 931 FMI 5 on machine monitor
• Possible engine shutdown in severe cases where ECM enters protective mode

Potential Causes

The most common technical causes for this fault code on used XCMG XE750D excavators include:

• Corroded or damaged sensor connector at the coolant reservoir—particularly vulnerable to coolant vapor exposure and moisture ingress
• Open circuit in wiring harness between coolant level sensor and ECM, often caused by harness chafing near the engine mount points or along the chassis frame
• Failed coolant level sensor due to internal component degradation (typical lifespan 3,000-5,000 operating hours in harsh conditions)
• Broken or frayed wires in the sensor pigtail, especially common where harness flexes near the radiator assembly
• Poor ground connection at sensor mounting point or ECM ground terminal
• ECM pin corrosion at the sensor circuit input terminals (less common but possible in high-humidity environments)

How to Troubleshoot and Fix Code 1627-5 SPN931 FMI5

Step 1: Visual Inspection Begin with a thorough inspection of the coolant level sensor located on the coolant expansion tank. Check the sensor connector for corrosion, pushed-out pins, or moisture contamination. On used excavators, examine the wiring harness routing from the sensor to the ECM for visible damage, especially where it contacts frame members or passes near hot engine components. Look for chafed insulation, exposed copper, or areas where zip ties have crushed the wire bundle.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and check resistance across sensor terminals (typical specification: 100-300 ohms at room temperature, but verify with XCMG service manual). Test continuity from sensor connector through the harness to the ECM pins—there should be less than 5 ohms resistance. Check for voltage supply at the sensor connector with ignition on (typically 5V reference voltage from ECM). Any open circuit or resistance above specifications indicates wiring problems.

Step 3: Component and Circuit Verification If wiring tests pass, substitute a known-good coolant level sensor to eliminate sensor failure. Before replacing any components on used machines, thoroughly clean all connector terminals with electrical contact cleaner and apply dielectric grease to prevent future corrosion. Use XCMG diagnostic software (or compatible J1939 scan tool) to monitor live sensor data and verify the ECM is receiving proper signals. Clear codes after repairs and perform a full operational test cycle.

Critical for Used Equipment: Inspect harness routing for modifications from previous repairs, aftermarket installations, or wear patterns indicating long-term vibration damage. Replace entire harness sections rather than splicing if multiple damage points exist.

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Disclaimer: This guide provides general troubleshooting information. Always consult the XCMG XE750D service manual for exact specifications and procedures. If unfamiliar with electrical diagnostics or heavy equipment systems, seek assistance from a certified XCMG technician or qualified diesel mechanic.