Sumitomo SH360HD-6 Fault Code 122: Meaning and Fix Guide

What is Sumitomo SH360HD-6 Fault Code 122?

Fault Code 122 on the Sumitomo SH360HD-6 excavator indicates a malfunction in the engine coolant temperature sensor circuit, specifically detecting an abnormally high voltage signal or open circuit condition. This code is generated when the Engine Control Module (ECM) receives a voltage reading outside the normal operating range from the coolant temperature sensor, typically above 4.8 volts.

The coolant temperature sensor plays a critical role in the SH360HD-6's performance management system. It provides real-time data to the ECM for fuel injection timing, idle speed control, and engine protection protocols. When this sensor circuit fails, the ECM cannot accurately monitor engine temperature, potentially leading to improper fuel delivery, increased emissions, and risk of engine overheating without proper warning.

Common Symptoms

When Code 122 is active on your Sumitomo SH360HD-6, you may experience:

• Check engine light or warning lamp illuminated on the instrument panel
• Engine running in limp mode with reduced power output and lower RPM ceiling
• Difficulty starting the engine, especially during cold weather conditions
• Erratic or inaccurate coolant temperature gauge readings (often showing cold or no reading)
• Cooling fans running continuously at high speed regardless of actual engine temperature
• Increased fuel consumption due to improper fuel mapping

Potential Causes

The most common technical reasons for Code 122 on used SH360HD-6 excavators include:

• Open circuit in the coolant temperature sensor wiring harness, often caused by wire chafing near the engine block mounting points
• Failed coolant temperature sensor (NTC thermistor) due to internal element breakage or corrosion
• Corroded or loose connector pins at the sensor or ECM interface points
• Damaged sensor wiring from rodent activity or exposure to hot exhaust components
• ECM internal fault (less common) affecting the 5-volt reference circuit
• Previous repair attempts with incorrect sensor specifications or poor-quality aftermarket sensors

How to Troubleshoot and Fix Code 122

Step 1: Visual Inspection Begin by inspecting the coolant temperature sensor located on the engine block (typically near the thermostat housing on Sumitomo models). Check the wiring harness for visible damage, especially where it routes near moving components or sharp edges. On used excavators, pay particular attention to connector corrosion and examine for coolant leaks that may have contaminated the sensor connector.

Step 2: Electrical Testing Disconnect the coolant temperature sensor connector. Using a digital multimeter, measure the resistance across the sensor terminals. At approximately 68°F (20°C), resistance should read between 2,000-3,000 ohms. If the reading shows infinite resistance (OL), the sensor has failed internally. Next, check the wiring harness by measuring continuity from the sensor connector to the ECM connector—resistance should be less than 5 ohms.

Step 3: Circuit Voltage Check With the sensor disconnected and ignition on (engine off), measure voltage at the harness connector going to the ECM. You should see approximately 5 volts on the signal wire. If voltage is absent or significantly different, suspect harness damage or an ECM issue. Check the ground circuit for less than 0.5 ohms resistance to chassis ground.

Step 4: Sensor Replacement and Verification If testing confirms sensor failure, replace with an OEM-equivalent sensor meeting Sumitomo specifications. For used excavators, always apply dielectric grease to connector terminals before reassembly to prevent future corrosion. Clear the fault code using diagnostic software (Sumitomo diagnostic tool or compatible OBD interface) and monitor for code recurrence during a complete heat cycle.

Professional Tip: Before replacing any components on used machinery, inspect all harness routing clips and ensure wires aren't rubbing against the engine block or frame—this is a common failure point on the SH360HD-6 that causes repeated sensor circuit issues.

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Disclaimer: This guide provides general troubleshooting information for Code 122. Always consult the official Sumitomo service manual for your specific machine serial number and consider professional diagnostic assistance for complex electrical issues or if you're unfamiliar with high-voltage systems.