What is XCMG General Fault Code 628-2?

Fault Code 628-2 on XCMG excavators indicates an abnormal signal or malfunction in the hydraulic oil temperature sensor circuit, specifically detecting a voltage reading that is too low or an open circuit condition. This diagnostic trouble code (DTC) is generated when the Electronic Control Module (ECM) receives sensor data outside the manufacturer's predetermined voltage range, typically below 0.5 volts for extended periods.

The hydraulic oil temperature sensor plays a critical role in XCMG excavators by monitoring fluid temperatures and protecting the hydraulic system from overheating damage. When this sensor circuit fails, the ECM cannot accurately regulate hydraulic pump output or activate cooling protocols, potentially leading to reduced machine efficiency and accelerated component wear in used equipment already experiencing normal degradation.

Common Symptoms

When fault code 628-2 is active, operators typically experience:

• Warning light illumination on the instrument cluster, often accompanied by a hydraulic system alert
• Reduced hydraulic performance or derated machine functions as the ECM enters failsafe mode
• Inaccurate or frozen hydraulic temperature readings on the display panel
• Increased hydraulic fan operation as the system defaults to maximum cooling
• Intermittent loss of auxiliary hydraulic functions during operation

Potential Causes

The most common technical reasons for code 628-2 in used XCMG excavators include:

• Damaged or corroded sensor connector at the hydraulic tank, especially common in machines operating in wet or corrosive environments
• Failed hydraulic oil temperature sensor due to internal element degradation or thermal cycling over time
• Wiring harness damage between the sensor and ECM, particularly at flex points near the hydraulic tank mounting area
• Broken or frayed wires caused by harness rubbing against frame components or hydraulic lines
• ECM internal fault affecting the sensor input circuit (less common but possible in older machines)
• Poor ground connections causing voltage drop in the sensor circuit

How to Troubleshoot and Fix Code 628-2

Step 1: Visual Inspection Begin by locating the hydraulic oil temperature sensor, typically mounted on the hydraulic tank. Inspect the sensor connector for corrosion, bent pins, or moisture intrusion. On used excavators, pay special attention to connector seals that may have hardened over time. Check the wiring harness routing for signs of abrasion, particularly where it contacts metal edges or moving components.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure resistance across the sensor terminals. Compare readings against XCMG specifications (typically 2,000-3,000 ohms at 20°C). Next, check circuit continuity from the sensor connector back to the ECM harness. Measure supply voltage at the sensor connector with ignition on—it should read approximately 5 volts. Any reading below 4.5 volts indicates wiring issues or ECM problems.

Step 3: Component Replacement and Verification If resistance values are out of specification or the sensor shows physical damage, replace the hydraulic oil temperature sensor with a genuine XCMG part. Before installation, apply dielectric grease to connector terminals to prevent future corrosion—critical for used machines. Clear the fault code using XCMG diagnostic software or a compatible scan tool, then operate the machine through a full work cycle to verify the repair.

Important Note for Used Equipment: Always inspect harness routing and secure any loose wiring away from moving parts or heat sources before concluding repairs, as previous owners may have performed modifications affecting original harness protection.

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Disclaimer: This guide provides general diagnostic information for XCMG fault code 628-2. Hydraulic and electrical systems can be dangerous. Always consult your machine's service manual and consider professional assistance from certified XCMG technicians for complex repairs, especially on used equipment with unknown service history.