What is Sany SY245/265H Fault Code 75?

Fault Code 75 on the Sany SY245/265H excavator indicates a malfunction in the engine coolant temperature sensor circuit or an abnormal temperature reading detected by the Mitsubishi Heavy Industries engine control module (ECM). This code is triggered when the ECM receives voltage signals outside the normal operating range from the coolant temperature sensor, typically between 0.5-4.5 volts.

This fault is critical because the coolant temperature sensor directly influences fuel injection timing, engine warm-up protocols, and protective shutdown systems. The Mitsubishi engine relies on accurate temperature data to optimize combustion efficiency and prevent overheating damage. When Code 75 appears, the ECM may default to a predetermined temperature value, causing poor fuel economy, rough idling, or activation of engine derate modes that limit machine productivity.

Common Symptoms

When Fault Code 75 is active on your Sany excavator, operators typically experience:

• Check Engine Light or warning lamp illuminated on the instrument cluster
• Hard starting conditions, especially during cold weather operation
• Black smoke from the exhaust due to improper fuel-air mixture calculations
• Engine overheating or failure to reach normal operating temperature
• Power derate mode engagement, limiting hydraulic system performance and digging force

Potential Causes

The most common technical reasons for Code 75 on used Sany SY245/265H excavators include:

• Faulty coolant temperature sensor with internal resistance drift (common after 5,000+ operating hours)
• Corroded or loose electrical connectors at the sensor harness junction near the thermostat housing
• Damaged wiring harness caused by rubbing against engine components or heat degradation from exhaust manifold proximity
• Low coolant levels causing sensor exposure to air instead of coolant
• ECM internal fault or corrupted calibration data (less common but possible in older machines)
• Aftermarket sensor installation with incorrect resistance specifications

How to Troubleshoot and Fix Code 75

Step 1: Visual Inspection Begin by inspecting the coolant temperature sensor located on the engine block near the thermostat housing. Check coolant levels first—low coolant is a frequent culprit in used machines. Examine the sensor connector for corrosion, moisture intrusion, or damaged pins. On older excavators, inspect the wiring harness for chafing points where it contacts metal brackets or hot engine surfaces.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure its resistance. At 20°C (68°F), resistance should read approximately 2,000-3,000 ohms (consult your Mitsubishi engine manual for exact specifications). Test the harness voltage with the ignition on—you should see approximately 5 volts reference voltage from the ECM. Any reading below 0.3V or above 4.8V indicates wiring problems or ECM issues.

Step 3: Component Replacement and Verification If sensor resistance is out of specification, replace it with an OEM Mitsubishi sensor (avoid aftermarket units with incorrect thermal curves). Clean all connector pins with electrical contact cleaner and apply dielectric grease. Clear the fault code using Mitsubishi MUT-III diagnostic software or a compatible scanner, then operate the machine through a full heat cycle to verify repair.

Disclaimer: This guide provides general troubleshooting information. Always consult the official Sany/Mitsubishi service manual and consider professional diagnostic assistance for complex electrical issues or if you're unfamiliar with high-voltage systems.