What is XCMG XE750D Fault Code 45663 SPN651 FMI6?

Fault Code 45663 (SPN651 FMI6) indicates a current below normal or open circuit condition in the J1939 data link communication system. This fault code specifically relates to the CAN bus communication network that allows the engine control module (ECM), hydraulic controllers, and display systems to exchange critical operational data. SPN 651 monitors the integrity of the J1939 serial data communication link, while FMI 6 signals that the electrical current is abnormally low or the circuit has an open connection.

For the XCMG XE750D excavator, this communication failure is critical because it disrupts real-time data exchange between the engine management system and machine controllers. When this code activates, the ECM cannot properly coordinate with hydraulic systems, potentially causing performance degradation or entering protective derate modes to prevent equipment damage.

Common Symptoms

• Warning lights illuminated on the instrument cluster, often accompanied by "Check Engine" or communication error messages
• Reduced engine power or hydraulic performance as the machine enters derate mode to protect systems
• Intermittent loss of gauge readings including RPM, fuel level, coolant temperature, or hydraulic pressure displays
• Erratic operation of electronic functions such as throttle response or automatic idle shutdown
• Complete failure of machine diagnostics or inability to communicate with diagnostic software tools

Potential Causes

On used XCMG XE750D excavators, this fault typically stems from physical deterioration of the CAN bus wiring harness. Common causes include:

• Damaged or corroded connectors at ECM, instrument cluster, or junction points where moisture infiltration causes high resistance
• Chafed or broken wiring along harness routing paths, especially near articulation points, cab mounts, or engine bay areas where vibration and heat cause insulation breakdown
• Failed termination resistors (120-ohm resistors) at CAN network endpoints that maintain proper signal integrity
• Faulty ECM or controller modules with internal communication circuit failures, more common in high-hour machines
• Poor ground connections at chassis or engine block grounding points causing voltage reference issues
• Aftermarket accessory installations that improperly tap into the CAN network creating signal interference

How to Troubleshoot and Fix Code 45663 SPN651 FMI6

Step 1: Visual Harness Inspection Begin with a thorough physical inspection of the J1939 CAN bus wiring harness. Trace the yellow and green twisted-pair communication wires from the ECM through junction boxes to the instrument cluster and other controllers. Look for obvious damage, chafing points where harnesses contact metal edges, melted insulation from exhaust heat, or connectors with corrosion or bent pins. Pay special attention to harness routing near hydraulic lines and moving components on used machines.

Step 2: Connector and Ground Testing Disconnect the main ECM connector and instrument cluster connectors. Inspect for moisture, corrosion (white or green deposits), or oil contamination in pin sockets. Clean connectors with electrical contact cleaner and apply dielectric grease. Using a digital multimeter, verify chassis ground integrity by measuring resistance between ECM ground pins and battery negative terminal—readings should be below 0.5 ohms. Check for voltage drops across ground connections under load conditions.

Step 3: CAN Bus Continuity and Resistance Check With all modules connected and ignition off, measure resistance between CAN High (CAN-H) and CAN Low (CAN-L) terminals at the ECM connector using a multimeter. You should read approximately 60 ohms (two 120-ohm termination resistors in parallel). Readings significantly higher indicate an open circuit or missing termination resistor; readings near zero suggest a short circuit. Disconnect modules one at a time to isolate the faulty segment. For used excavators, check termination resistors at network endpoints, as these components fail over time.

Step 4: Advanced Diagnostics with XCMG Software Connect XCMG diagnostic software or compatible J1939 scan tool to the machine's diagnostic port. Monitor live CAN bus traffic and verify all controllers are communicating. Check for intermittent dropouts or error rates exceeding 5%. Perform bidirectional tests commanding specific modules to verify two-way communication. If software cannot establish communication, suspect ECM failure or main harness breaks. Freeze frame data may reveal if the fault occurs during specific operating conditions like high vibration or temperature extremes.

Step 5: Component Replacement and Verification If diagnostics identify a specific failed component, replace the ECM, damaged harness section, or faulty controller module. When replacing harnesses on used machines, route new wiring away from sharp edges and secure with proper grommets and protective loom. After repairs, clear fault codes and operate the machine through a complete work cycle, monitoring for code recurrence. Verify all instrument displays function correctly and diagnostic software shows clean communication with all modules.

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Disclaimer: This guide provides general troubleshooting information for educational purposes. Always consult the official XCMG XE750D service manual and qualified heavy equipment technicians for diagnosis and repair. Improper repairs to electronic systems can cause further damage or safety hazards.