What is Sany SY245/265H Fault Code 112?

Fault Code 112 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 an abnormally high voltage signal from the intake air temperature sensor, typically exceeding 4.5-4.8 volts for more than 2 seconds.

The IAT sensor plays a critical role in engine performance by monitoring the temperature of air entering the combustion system. The ECM uses this data to calculate proper fuel injection timing and air-fuel ratios. When Code 112 activates, the engine management system cannot accurately determine intake air density, leading to suboptimal combustion efficiency and potential engine protection measures being enacted.

Common Symptoms

• Check Engine Light or malfunction indicator lamp illuminated on the instrument cluster
• Noticeable loss of engine power or power derate mode activation, especially under heavy load conditions
• Rough idling or irregular engine performance during cold starts
• Increased black smoke from exhaust due to improper fuel mixture calculations
• Higher-than-normal fuel consumption as the ECM defaults to a preset "limp mode" fuel map

Potential Causes

The high voltage reading typically results from an open circuit condition. Common causes in used Sany excavators include:

• Damaged or disconnected IAT sensor wiring harness, particularly at flex points near the air intake manifold where vibration causes wire fatigue
• Corroded or loose connector pins at the sensor plug—a frequent issue in machines operating in humid or dusty environments
• Failed intake air temperature sensor with internal open circuit (less common than wiring issues)
• Chafed wiring where the harness contacts the engine block or frame rails (known wear point on SY245/265H models)
• Previous repair attempts using incorrect connector seals allowing moisture intrusion
• ECM internal fault (rare, but possible in high-hour used machines)

How to Troubleshoot and Fix Code 112

Step 1: Visual Inspection Begin with a thorough inspection of the IAT sensor and its wiring harness from the sensor to the ECM. Look specifically for abraded insulation, broken wires, or corroded connectors. On used excavators, check common rub points where the harness passes near moving components or sharp edges.

Step 2: Connector and Sensor Testing Disconnect the IAT sensor connector and inspect pins for corrosion, bent terminals, or moisture. Clean with electrical contact cleaner if needed. Using a digital multimeter, measure the sensor resistance across its terminals. At 68°F (20°C), resistance should typically read 2,000-3,000 ohms (consult your service manual for exact specifications). An infinite (open) reading indicates sensor failure.

Step 3: Circuit Voltage Testing With the sensor disconnected and ignition on (engine off), measure voltage at the ECM-side harness connector. You should see approximately 5 volts on the signal wire (reference voltage from ECM). If voltage is absent or incorrect, trace the harness for breaks or check ECM power supply circuits.

Step 4: Resistance and Continuity Checks Measure continuity between the sensor ground wire and chassis ground—it should show less than 1 ohm resistance. High resistance indicates a poor ground connection. Also verify continuity through the signal wire from sensor connector to ECM pin (consult wiring diagram for pin location).

Step 5: Component Replacement If sensor tests fail, replace the IAT sensor with OEM or quality aftermarket parts. For used excavators with high hours, consider replacing the sensor connector pigtail simultaneously to prevent future corrosion issues. After replacement, clear codes using diagnostic software compatible with Mitsubishi engines (such as MUT-III or equivalent aftermarket scan tools) and perform a test run under load.

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Disclaimer: This guide provides general troubleshooting information for educational purposes. Always consult the manufacturer's official service manual and safety procedures. If you're unfamiliar with electrical diagnostics or working around diesel engines, seek assistance from a qualified heavy equipment technician to prevent injury or further machine damage.