What is XCMG XE750D Fault Code 2604-5 SPN3660 FMI5?

Fault Code 2604-5 (SPN 3660, FMI 5) indicates an Aftertreatment Diesel Exhaust Fluid (DEF) Pump Motor Current Below Normal or Open Circuit condition on the XCMG XE750D excavator. This code is triggered when the Engine Control Module (ECM) detects abnormally low electrical current flowing through the DEF pump motor circuit, suggesting a wiring fault, poor connection, or internal pump motor failure.

The DEF system is critical for meeting emissions regulations by injecting urea solution into the exhaust stream for Selective Catalytic Reduction (SCR). On the XE750D's diesel engine platform, this system must maintain precise dosing control. When SPN 3660 with FMI 5 (current below normal/open circuit) appears, the SCR system cannot function properly, potentially triggering engine derate to protect the aftertreatment components and ensure compliance.

Common Symptoms

• Amber or red exhaust aftertreatment warning light illuminated on the instrument cluster
• Engine power derate (reduced horsepower/torque) after a predetermined operating period
• DEF pump inoperative – no audible pump operation during key-on or regeneration cycles
• Additional fault codes related to SCR system performance or DEF quality may appear simultaneously
• Operator notification on display screen warning of emissions system malfunction

Potential Causes

On used XCMG XE750D excavators, this fault typically stems from:

• Open circuit in DEF pump motor wiring harness – particularly where harness routes near frame rails or engine mounts (common wear point)
• Corroded or loose electrical connectors at the DEF pump motor or ECM interface
• Failed DEF pump motor with internal winding damage or seized bearings
• Damaged ECM driver circuit for the DEF pump (less common but possible on high-hour machines)
• Chafed wiring from rubbing against chassis components or improper previous repairs
• Blown fuse or faulty relay in the DEF system power supply circuit

How to Troubleshoot and Fix Code 2604-5 SPN3660 FMI5

Step 1: Visual Inspection Locate the DEF pump (typically mounted near the DEF tank on the right side of the machine). Inspect the electrical connector for corrosion, bent pins, or moisture intrusion. On used excavators, check the entire wiring harness routing for abrasion points, especially where it passes through bulkheads or near moving components.

Step 2: Electrical Testing Disconnect the DEF pump motor connector. Using a digital multimeter, measure resistance across the pump motor terminals (typically 3-8 ohms for most pumps). An open circuit (infinite resistance) confirms internal motor failure. Next, check for continuity from the harness connector back to the ECM pins (consult XCMG wiring diagrams). Repair or replace any wiring showing high resistance or breaks.

Step 3: Power Supply Verification With ignition on (engine off), measure voltage at the pump connector – should read battery voltage (12V) when ECM commands pump activation. Use XCMG diagnostic software or compatible scan tool to manually activate the DEF pump. No voltage indicates ECM driver circuit failure or upstream power supply issue (check fuses/relays).

Step 4: Component Replacement If wiring tests pass but motor resistance is out of spec, replace the DEF pump assembly. For used machines, always replace the connector pigtail with OEM or quality aftermarket parts to prevent recurring corrosion issues. Clear codes and perform a SCR system function test using diagnostic software.

Critical for Used Equipment: Before replacing the pump, thoroughly clean all electrical connections with contact cleaner and apply dielectric grease. Many used XE750D excavators develop this fault from connector corrosion rather than actual component failure.

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Disclaimer: This guide provides general troubleshooting information. Always consult the official XCMG service manual for your specific machine serial number and software calibration. If unfamiliar with high-voltage electrical systems or emissions components, seek assistance from a certified heavy equipment technician.