What is Sany SY245/265H Fault Code 105?

Fault Code 105 on the Sany SY245/265H excavator indicates an Intake Air Temperature (IAT) Sensor Circuit High Voltage condition in the Mitsubishi Heavy Industries diesel engine. This diagnostic trouble code (DTC) is triggered when the Engine Control Module (ECM) detects a voltage signal from the IAT sensor that exceeds the manufacturer's predetermined threshold, typically above 4.5-5.0 volts.

The IAT sensor plays a critical role in engine performance by monitoring the temperature of air entering the combustion chamber. The ECM uses this data to calculate optimal fuel injection timing and air-fuel ratios. When Code 105 appears, the ECM cannot accurately determine intake air density, which can lead to inefficient combustion, increased emissions, and potential engine damage in the Mitsubishi powerplant. This is particularly critical in high-performance excavators like the SY245/265H, where precise fuel management directly impacts hydraulic system efficiency and operational costs.

Common Symptoms

When Fault Code 105 is active, operators typically experience:

• Check Engine Light or malfunction indicator lamp illuminated on the instrument cluster
• Reduced engine power or derate mode activation, limiting maximum RPM and hydraulic performance
• Hard starting conditions, especially in cold weather when accurate air temperature readings are most critical
• Black smoke from the exhaust due to overfueling from incorrect air density calculations
• Poor fuel economy and noticeably increased diesel consumption during normal operations

Potential Causes

The most common technical reasons for Code 105 in used Sany excavators include:

• Open circuit in the IAT sensor wiring harness, often caused by rodent damage or insulation breakdown
• Failed IAT sensor with internal resistance degradation (common after 5,000+ operating hours)
• Corroded or loose connector pins at the sensor or ECM interface—particularly problematic in high-moisture environments
• Damaged wiring at known rub points near the air intake manifold where harnesses contact metal edges
• ECM internal fault (rare, but possible in machines with electrical system history)
• Aftermarket air filter housing modifications that damaged original sensor wiring during installation

How to Troubleshoot and Fix Code 105

Step 1: Visual Inspection Begin with a thorough inspection of the IAT sensor located in the intake manifold. Check the electrical connector for corrosion, bent pins, or moisture intrusion. On used excavators, examine the entire wiring harness from sensor to ECM for chafing, especially where it routes near sharp edges or moving components. Clean all connections with electrical contact cleaner before proceeding.

Step 2: Sensor Resistance Testing Disconnect the IAT sensor connector and measure sensor resistance using a digital multimeter. At 68°F (20°C), a functioning Mitsubishi IAT sensor should read approximately 2,000-3,000 ohms. Compare your reading against the manufacturer's temperature-resistance chart. If the reading shows infinite resistance (open circuit) or significantly deviates from specifications, replace the sensor.

Step 3: Circuit Voltage Testing With the ignition on and sensor disconnected, check for reference voltage at the harness connector (ECM side). You should measure approximately 5 volts on the signal wire. If voltage reads near battery voltage (12V+) or remains at 5V when the circuit is grounded, suspect wiring issues or an ECM problem. Use Mitsubishi diagnostic software (MUT-III or compatible) to monitor live sensor data and verify the ECM is receiving proper signals.

Step 4: Harness Continuity Check Test continuity between the sensor connector and ECM pins, referring to the wiring diagram for your specific serial number. Pay special attention to the ground circuit integrity—a high-resistance ground can cause voltage reading errors. For used machines, consider replacing corroded connectors rather than cleaning them, as corrosion often returns quickly in harsh environments.

Disclaimer: This guide provides general troubleshooting information for experienced technicians. Always consult the official Sany service manual and Mitsubishi engine documentation for your specific machine serial number. If you lack proper diagnostic tools or experience with electronic fuel systems, consult a certified Sany dealer or qualified heavy equipment technician to avoid misdiagnosis and unnecessary parts replacement.