What is Sany SY245/265H Fault Code 122?

Fault Code 122 on the Sany SY245/265H excavator indicates a Fuel Injection Pump Position Sensor (also called the Fuel Control Actuator Sensor) malfunction or circuit error within the Mitsubishi Heavy Industries diesel engine system. This diagnostic trouble code (DTC) is triggered when the Engine Control Module (ECM) detects an abnormal voltage signal, open circuit, or short circuit from the fuel pump's position feedback sensor.

The fuel injection pump position sensor provides critical real-time data to the ECM about the fuel control rack position, enabling precise fuel delivery and engine speed control. When this sensor fails or sends erratic signals, the ECM cannot accurately regulate fuel injection timing and volume, which directly impacts engine performance, fuel efficiency, and emissions control. For used excavators, this fault often stems from sensor degradation, wiring harness damage from heat and vibration exposure, or connector corrosion—common issues in machines with significant operating hours.

Common Symptoms

• Check Engine Light or malfunction indicator lamp illuminated on the instrument cluster
• Engine power derate or noticeable loss of horsepower, especially under load
• Rough idling or unstable engine RPM fluctuations at low speeds
• Hard starting or extended cranking time, particularly when the engine is cold
• Black smoke from the exhaust due to improper fuel metering

Potential Causes

• Faulty fuel injection pump position sensor due to internal wear or heat damage (common in high-hour used machines)
• Damaged or frayed wiring harness between the sensor and ECM, particularly at flex points near the engine mount
• Corroded or loose electrical connectors at the sensor or ECM connection points (moisture intrusion is common)
• ECM internal fault or software calibration issue (less common but possible in older units)
• Poor ground connection causing voltage reference errors
• Fuel contamination causing mechanical binding of the fuel control actuator

How to Troubleshoot and Fix Code 122

Step 1: Visual Inspection
Begin with a thorough inspection of the fuel injection pump position sensor and its wiring harness. Check for visible damage, chafing against engine components, melted insulation from exhaust heat exposure, or oil contamination on connectors. For used excavators, pay special attention to harness routing near vibration points and heat sources.

Step 2: Electrical Testing
Using a digital multimeter, check the sensor's resistance and voltage output according to Mitsubishi specifications (typically 0.5-4.5V range depending on position). Disconnect the sensor connector and measure resistance across sensor terminals—readings outside the 500-2000 ohm range usually indicate sensor failure. Test continuity of all wires from sensor to ECM and verify proper ground integrity (less than 1 ohm resistance to chassis ground).

Step 3: Connector and Pin Inspection
Remove connector housings and inspect for corrosion, bent pins, or moisture. Clean contacts with electrical contact cleaner and apply dielectric grease. This step is crucial for used machines where environmental exposure has accumulated over years.

Step 4: Sensor Replacement and Calibration
If testing confirms sensor failure, replace with a genuine Mitsubishi or OEM-equivalent fuel injection pump position sensor. After installation, clear fault codes using diagnostic software (Mitsubishi MUT-III or compatible scanner) and perform an idle learn procedure to ensure proper ECM calibration.

Disclaimer: This guide provides general troubleshooting information. Always consult the official Sany service manual and consider professional diagnostic assistance for complex electrical issues or if you lack proper diagnostic tools.