What is XCMG General Fault Code 108-4?

Fault Code 108-4 on XCMG excavators indicates a Low Voltage Condition on the Main Hydraulic Pump Solenoid Circuit. This diagnostic trouble code (DTC) is triggered when the Electronic Control Module (ECM) detects voltage levels below the manufacturer's specified threshold, typically under 9-10 volts during normal operation.

This code affects the main hydraulic pump's electronic control system, which regulates flow and pressure throughout the excavator's hydraulic circuit. The proportional solenoid valve relies on precise voltage signals to modulate hydraulic output based on operator inputs. When voltage drops below acceptable parameters, the ECM cannot properly control pump displacement, leading to erratic hydraulic performance or complete system shutdown. For XCMG machines—particularly used units with extended operating hours—this fault directly impacts productivity and can indicate deteriorating electrical infrastructure that requires immediate attention.

Common Symptoms

• Reduced hydraulic power across all functions (boom, arm, bucket, and swing operations become sluggish or unresponsive)
• Intermittent loss of hydraulic function, especially during cold starts or high electrical load conditions
• Dashboard warning light illumination with possible audible alarm from the cab
• Engine derating or refusal to increase RPM beyond idle in severe cases
• Erratic hydraulic response where implement movements don't match joystick inputs smoothly

Potential Causes

The most common technical causes for Code 108-4 on used XCMG excavators include:

• Corroded or loose electrical connections at the pump solenoid connector (common failure point due to exposure to hydraulic oil mist and moisture)
• Damaged wiring harness between the ECM and hydraulic pump, particularly at routing points near the engine bay where vibration causes insulation wear
• Failing proportional solenoid valve within the main pump assembly showing increased internal resistance
• Weak battery or poor charging system performance causing system-wide voltage drops under load
• ECM ground circuit issues or corroded chassis ground points reducing voltage supply
• Aftermarket electrical accessories improperly installed that create excessive current draw

How to Troubleshoot and Fix Code 108-4

Step 1: Visual Inspection and Voltage Verification Begin by performing a thorough visual inspection of the main pump solenoid harness from the ECM to the hydraulic pump. Look for abraded insulation, pinched wires at mounting brackets, or oil-saturated connectors. Using a digital multimeter (DMM), measure battery voltage with the engine running—it should read 13.5-14.5 volts. If voltage is low, address the charging system (alternator/belt) before proceeding.

Step 2: Connector and Resistance Testing Disconnect the solenoid connector at the hydraulic pump. Inspect pins for corrosion, bent terminals, or moisture intrusion—common issues in used excavators. Clean contacts with electrical contact cleaner and apply dielectric grease. Measure solenoid resistance across terminals; typical specifications range from 8-15 ohms (consult XCMG service manual for exact values). Resistance outside this range indicates solenoid failure.

Step 3: Circuit Voltage Drop Testing With the connector reconnected and ignition on (engine off), back-probe the solenoid connector using your DMM. Command the pump solenoid active using XCMG diagnostic software (or have an assistant operate controls). Measure voltage at the solenoid—it should match battery voltage within 0.5 volts. Excessive voltage drop indicates high resistance in the supply circuit, damaged harness, or poor ECM output. For used machines, pay special attention to harness routing where friction against the engine block or hydraulic reservoir commonly causes wire damage.

Step 4: ECM and Ground Circuit Verification If solenoid and harness test satisfactorily, verify all ECM ground connections are clean and tight. Measure resistance from ECM ground pin to battery negative—it should be less than 0.1 ohms. Finally, use diagnostic software to monitor real-time solenoid command vs. actual voltage delivery, which can reveal intermittent ECM driver circuit failures.

---

Disclaimer: This guide provides general diagnostic procedures for Code 108-4. Always consult the official XCMG service manual for your specific model year and serial number. If you lack proper diagnostic tools or electrical troubleshooting experience, consult a certified XCMG technician to prevent equipment damage or safety hazards.