Sumitomo SH380LHD-6 Fault Code 122: Complete Diagnostic Guide

What is Sumitomo SH380LHD-6 Fault Code 122?

Fault Code 122 on the Sumitomo SH380LHD-6 indicates a malfunction in the engine coolant temperature sensor circuit or an abnormal coolant temperature reading detected by the ECM (Engine Control Module). This code triggers when the temperature sensor sends voltage signals outside the expected range, or when the sensor circuit experiences an electrical fault such as an open or short.

The engine coolant temperature sensor is critical for the SH380LHD-6's performance management. The ECM relies on accurate coolant temperature data to optimize fuel injection timing, control engine protection systems, and manage hydraulic oil temperature. When this sensor fails or provides incorrect readings, the machine may enter derate mode to prevent potential engine damage from overheating or run inefficiently due to improper fuel mapping.

Common Symptoms

When Code 122 is active on your Sumitomo SH380LHD-6, operators typically experience:

• Engine warning light illuminated on the instrument panel, often accompanied by a temperature warning icon
• Reduced engine power or automatic derate mode activation, limiting machine performance
• Cooling fan running continuously at high speed, even when engine temperature appears normal
• Hard starting or rough idle, especially during cold starts when the ECM cannot properly adjust fuel delivery
• Inaccurate temperature gauge readings on the dashboard, showing extremes (very hot or very cold) that don't match actual conditions

Potential Causes

Several technical issues commonly trigger Code 122 on used SH380LHD-6 excavators:

• Failed coolant temperature sensor due to internal resistance degradation (common after 5,000+ operating hours)
• Corroded or damaged wiring harness connectors at the sensor connection point, particularly where the harness routes near the exhaust manifold
• Chafed or pinched sensor wiring caused by vibration wear against the engine block or frame—a known issue on older Sumitomo models
• ECM ground circuit issues affecting sensor voltage reference signals
• Coolant contamination causing sensor element coating or failure
• Faulty ECM (rare, but possible in high-hour machines with electrical system history)

How to Troubleshoot and Fix Code 122

Step 1: Visual Inspection Begin by inspecting the coolant temperature sensor location (typically on the engine block near the thermostat housing). Check the wiring harness for visible damage, rubbing points, or corrosion. On used excavators, pay special attention to connector pins for green corrosion or bent terminals—clean with electrical contact cleaner if necessary.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor connector and measure resistance across the sensor terminals. At room temperature (68°F/20°C), resistance should typically read between 2,000-3,000 ohms (consult your service manual for exact specifications). Test the harness continuity from the sensor connector back to the ECM—readings should show less than 5 ohms resistance and infinite resistance to ground.

Step 3: Live Data Analysis Connect Sumitomo diagnostic software or a compatible scanner to monitor live coolant temperature readings. Compare the sensor reading to actual engine temperature using an infrared thermometer. A variance greater than 10°F indicates sensor failure.

Step 4: Component Replacement If testing confirms sensor failure, replace with a genuine Sumitomo or OEM-equivalent sensor. For used machines, always replace the connector pigtail simultaneously, as connector corrosion often returns even after cleaning. Apply dielectric grease to new connections to prevent moisture intrusion.

Step 5: Clear Codes and Verify After repairs, clear fault codes using diagnostic software, run the engine through a complete heat cycle, and verify Code 122 does not return.

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Disclaimer: This guide provides general diagnostic information. Always consult the official Sumitomo service manual for your specific machine serial number. If you're uncomfortable performing electrical diagnostics, contact a certified Sumitomo technician to prevent further damage to your excavator's systems.