What is XCMG General Fault Code A108?

Fault Code A108 indicates a malfunction in the engine coolant temperature sensor circuit or an out-of-range coolant temperature reading. This code is triggered when the Electronic Control Module (ECM) detects voltage signals from the coolant temperature sensor that fall outside the expected parameters, typically indicating either a circuit failure, sensor degradation, or actual engine overheating conditions.

In XCMG excavators, the coolant temperature sensor plays a critical role in engine management by providing real-time data that influences fuel injection timing, throttle response, and protective shutdown sequences. When this sensor fails or sends erratic signals, the ECM cannot properly regulate engine performance, potentially leading to inefficient combustion, increased emissions, or catastrophic engine damage if overheating goes undetected.

Common Symptoms

When fault code A108 is active, operators typically experience:

• Illuminated engine warning light or check engine indicator on the dashboard
• Engine derate mode where maximum RPM and power output are significantly reduced
• Erratic temperature gauge readings that fluctuate unexpectedly or remain stuck at one position
• Difficult cold starts or rough idling, particularly in cooler weather conditions
• Activation of cooling fans at maximum speed even when engine temperature appears normal

Potential Causes

The most common technical reasons for A108 in used XCMG excavators include:

• Degraded coolant temperature sensor due to age, corrosion, or thermal cycling stress
• Damaged wiring harness near the sensor connector, particularly where cables route near sharp edges or moving components
• Corroded or loose electrical connectors at the sensor or ECM interface points
• Contaminated engine coolant affecting sensor accuracy or causing mineral deposits on the sensor element
• ECM software glitches or internal circuit board failures (less common but possible in high-hour machines)
• Faulty ground connections in the sensor circuit causing voltage reference issues

How to Troubleshoot and Fix Code A108

Step 1: Visual Inspection Begin by inspecting the coolant temperature sensor and its wiring harness for obvious damage. On used excavators, check for wire insulation cracking, connector corrosion (white or green deposits), and harness routing near wear points. Clean all connectors with electrical contact cleaner and ensure tight connections.

Step 2: Sensor Resistance Testing Disconnect the sensor and use a digital multimeter to measure resistance across the sensor terminals. Compare readings against XCMG specifications (typically 2,000-3,000 ohms at 20°C). Test at different temperatures if possible; resistance should decrease predictably as temperature rises.

Step 3: Circuit Voltage Check With the sensor disconnected and ignition on, measure voltage at the harness connector. You should see approximately 5 volts reference voltage from the ECM. No voltage indicates wiring issues or ECM problems.

Step 4: Harness Continuity Testing Test for continuity between the sensor connector and ECM pins, and check for shorts to ground. In used machines, pay special attention to harness sections that pass near the engine block or hydraulic lines where friction wear commonly occurs.

Step 5: Coolant System Evaluation Verify coolant level and condition. Old, contaminated coolant can cause sensor fouling. If the sensor has mineral buildup, replacement is recommended even if electrical tests pass.

Disclaimer: This guide provides general troubleshooting information. Always consult XCMG service manuals and qualified diesel technicians for machine-specific procedures. Improper repairs may void warranties or create safety hazards.