What is XCMG XE750D Fault Code 2602-5 SPN3659 FMI5?

Fault Code 2602-5 (SPN 3659 FMI 5) indicates a current below normal or open circuit condition in the Diesel Exhaust Fluid (DEF) Pump Motor circuit. This code specifically points to insufficient electrical current reaching the DEF pump motor, which is responsible for delivering diesel exhaust fluid to the Selective Catalytic Reduction (SCR) system on the XCMG XE750D excavator.

This fault is critical for emissions compliance and machine performance. The SCR system requires precise DEF injection to reduce harmful nitrogen oxide (NOx) emissions. When the ECM (Engine Control Module) detects current flow below the expected threshold (FMI 5), it triggers this code. On used excavators, this issue often stems from degraded wiring, corroded connectors, or a failing DEF pump motor itself—all common in machines with significant operating hours in harsh construction environments.

Common Symptoms

• Check Engine Light (CEL) or DEF system warning light illuminated on the instrument cluster
• Engine derate or reduced power output after a grace period (typically preventing full throttle operation)
• DEF consumption drops to zero or becomes inconsistent, visible through machine diagnostics
• Error messages on the display screen specifically referencing the SCR or DEF system
• Machine may enter limp mode after extended operation with the active fault, limiting productivity

Potential Causes

• Open circuit or damaged wiring in the DEF pump motor harness (common rub points near the fuel tank or chassis frame on used machines)
• Corroded or loose electrical connectors at the DEF pump motor or ECM (moisture intrusion from aging seals)
• Failed DEF pump motor due to internal winding damage or bearing seizure
• Blown fuse or faulty relay in the DEF pump power supply circuit
• ECM internal driver circuit failure (less common, but possible in high-hour machines)
• Damaged harness from rodent activity or physical impact during operation

How to Troubleshoot and Fix Code 2602-5 SPN3659 FMI5

Step 1: Visual Inspection Begin with a thorough inspection of the DEF pump motor wiring harness from the ECM to the pump. On used excavators, check for chafed insulation, broken wires, or evidence of harness contact with moving components or hot surfaces. Inspect all connectors for corrosion, bent pins, or moisture intrusion—particularly at the pump motor connector.

Step 2: Electrical Testing Using a digital multimeter, disconnect the DEF pump motor connector and check for continuity in the wiring between the ECM and pump (typically 2-3 ohms resistance maximum). Test for voltage supply at the pump connector with ignition on—should read battery voltage (approximately 24V on this model). Check the ground circuit for less than 0.5 ohms resistance to chassis ground.

Step 3: Component Testing Measure the DEF pump motor resistance directly at the motor terminals (consult service manual for specifications, typically 3-8 ohms). If readings are infinite (open circuit) or zero (short circuit), replace the pump motor. Verify fuse integrity in the DEF system power supply circuit using a multimeter.

Step 4: Advanced Diagnostics Connect XCMG diagnostic software or compatible J1939 scan tool to monitor live data from the DEF system. Check for commanded pump operation versus actual current draw. For used excavators, perform a harness wiggle test while monitoring data—intermittent faults often appear during connector movement.

Step 5: Repair and Verification Replace damaged wiring, connectors, or the DEF pump motor as diagnosed. Apply dielectric grease to all connectors to prevent future corrosion. Clear fault codes and perform a stationary regeneration if required. Test operate the machine under load to confirm the fault does not return.

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Disclaimer: This guide provides general diagnostic information for XCMG XE750D fault code 2602-5. Always consult the manufacturer's service manual and safety procedures. For used excavators with complex electrical issues or persistent faults, professional diagnosis by a certified XCMG technician with proper diagnostic equipment is strongly recommended.