What is Sany SY245/265H Fault Code 108?

Fault Code 108 on the Sany SY245/265H excavator indicates an Engine Coolant Temperature (ECT) Sensor Circuit High Voltage condition. This diagnostic trouble code (DTC) is triggered when the Mitsubishi Heavy Industries engine ECM detects a voltage reading from the coolant temperature sensor circuit that exceeds the manufacturer's predetermined threshold, typically above 4.8-5.0 volts.

The ECT sensor is a critical component in the engine management system, providing real-time data about coolant temperature to the Electronic Control Module (ECM). This information directly influences fuel injection timing, idle speed control, and engine protection protocols. On used excavators with Mitsubishi diesel engines, this code can lead to improper fuel mapping and potential overheating if left unaddressed, making accurate temperature monitoring essential for engine longevity.

Common Symptoms

When Code 108 is active on your Sany excavator, operators typically experience:

• Engine warning lamp illuminated on the instrument cluster, often accompanied by reduced engine performance
• Hard starting conditions, especially when the engine is cold, due to incorrect fuel enrichment calculations
• Rough idle or erratic engine RPM as the ECM defaults to failsafe temperature values
• Cooling fan running continuously at high speed, regardless of actual engine temperature
• Engine derate mode activation in severe cases, limiting machine productivity and hydraulic performance

Potential Causes

The most common technical reasons for Code 108 on used Sany SY245/265H excavators include:

• Open circuit in ECT sensor wiring harness, particularly at flex points near the engine block or valve cover where vibration causes wire fatigue
• Failed coolant temperature sensor with internal resistance breakdown (common after 5,000+ operating hours)
• Corroded or damaged sensor connector pins, especially on machines operated in high-moisture or coastal environments
• Chafed wiring rubbing against engine components, creating intermittent short-to-voltage conditions
• ECM internal fault (rare but possible on older machines with 8,000+ hours)
• Poor ground connection at the engine block ground strap, affecting sensor reference voltage

How to Troubleshoot and Fix Code 108

Step 1: Visual Inspection Begin by inspecting the ECT sensor located on the engine block (typically near the thermostat housing on Mitsubishi engines). Check the sensor connector for corrosion, moisture intrusion, or bent pins. On used excavators, carefully trace the sensor harness for signs of chafing, particularly where it routes near hot exhaust components or vibrating engine mounts.

Step 2: Electrical Testing Disconnect the ECT sensor connector and use a digital multimeter to measure resistance across the sensor terminals. At 68°F (20°C), resistance should read approximately 2,000-3,000 ohms (consult your service manual for exact specifications). Next, check for supply voltage at the harness connector with ignition on—you should see approximately 5 volts. If voltage reads at or near battery voltage (12-24V), suspect a short-to-power condition in the wiring.

Step 3: Circuit and Ground Verification Test continuity between the sensor signal wire and ECM pin (refer to wiring diagrams). Measure resistance to ground on the signal wire—infinite resistance indicates proper insulation. Check the engine ground strap connection; clean and tighten if necessary, as poor grounds commonly cause high voltage readings on used machinery.

Step 4: Component Replacement If testing confirms sensor failure, replace the ECT sensor using OEM or quality aftermarket parts. Apply dielectric grease to connector pins to prevent future corrosion. Clear codes using Mitsubishi MUT-III diagnostic software or compatible scan tool, then perform a test cycle to verify repair.

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Disclaimer: This guide provides general troubleshooting information. Always consult your Sany service manual and consider professional diagnostic assistance for complex electrical issues, especially on machines still under warranty or service agreements.