What is XCMG XE750D Fault Code 45782 SPN655 FMI5?

Fault Code 45782 (SPN655 FMI5) indicates an Engine Coolant Temperature (ECT) sensor circuit current below normal or open circuit condition on the XCMG XE750D excavator. This diagnostic trouble code (DTC) is triggered when the Engine Control Module (ECM) detects abnormally low current flow through the coolant temperature sensor circuit, typically indicating an open circuit, high resistance, or sensor failure.

SPN 655 specifically monitors the engine coolant temperature sensor, while FMI 5 designates a current below normal or open circuit fault. This code is critical because the ECM relies on accurate coolant temperature data to control fuel injection timing, idle speed, engine protection systems, and diagnostic functions. On used XCMG excavators, this sensor failure can trigger engine derate modes or prevent cold-start enrichment, severely impacting machine productivity.

Common Symptoms

• Check Engine Light or malfunction indicator lamp (MIL) illuminated on the instrument cluster
• Engine runs excessively rich or lean, causing rough idle or black smoke from exhaust
• Difficulty starting in cold weather due to improper fuel enrichment
• Engine derate mode activated, limiting power output and hydraulic performance
• Cooling fan runs continuously at high speed regardless of actual engine temperature

Potential Causes

The most common technical reasons for Code 45782 on used XCMG XE750D excavators include:

• Damaged or corroded wiring harness between the ECT sensor and ECM, particularly at harness rub points near the engine block or frame rails
• Failed coolant temperature sensor due to internal open circuit or age-related degradation
• Loose or corroded electrical connectors at the sensor or ECM terminals (common in machines with 5,000+ operating hours)
• Broken or chafed wires in the sensor signal circuit caused by vibration or improper previous repairs
• ECM internal fault affecting the sensor supply voltage circuit (rare but possible on high-hour machines)

How to Troubleshoot and Fix Code 45782 SPN655 FMI5

Step 1: Visual Inspection Perform a thorough inspection of the ECT sensor wiring harness from the sensor to the ECM. On used excavators, check for wire chafing at known rub points near engine mounts and hydraulic lines. Inspect the sensor connector for corrosion, moisture intrusion, or bent pins.

Step 2: Electrical Testing Disconnect the coolant temperature sensor connector. Using a digital multimeter (DMM), measure resistance across the sensor terminals. A functioning sensor typically reads 2,000-3,000 ohms at room temperature. An infinite (open) reading confirms sensor failure. Check continuity in the wiring harness between the sensor connector and ECM pins to identify open circuits.

Step 3: Sensor Replacement and Verification Replace the ECT sensor if resistance values are out of specification or the circuit shows an open condition. Before installing the new sensor, apply dielectric grease to connector terminals to prevent future corrosion. Clear fault codes using XCMG diagnostic software or a compatible scan tool, then run the engine through temperature cycles to verify repair.

Disclaimer: This guide provides general troubleshooting information. Always consult the XCMG XE750D service manual and consider professional diagnostic assistance for complex electrical issues or if unfamiliar with high-voltage systems.