Sumitomo SH210-6 Fault Code 122: Complete Diagnostic Guide

What is Sumitomo SH210-6 Fault Code 122?

Fault Code 122 on the Sumitomo SH210-6 excavator indicates a malfunction in the Engine Coolant Temperature (ECT) Sensor circuit or an abnormal temperature reading outside the acceptable range. This code is triggered when the Engine Control Module (ECM) detects voltage signals from the coolant temperature sensor that are either too high, too low, or erratic, preventing accurate engine temperature monitoring.

The ECT sensor plays a critical role in the SH210-6's engine management system by providing real-time coolant temperature data to the ECM. This information directly influences fuel injection timing, idle speed control, and engine protection protocols. On used excavators, this fault can lead to improper engine performance, reduced fuel efficiency, and potential overheating damage if left unaddressed.

Common Symptoms

When Code 122 is active on your Sumitomo SH210-6, operators typically experience:

• Check Engine Light or malfunction indicator illuminated on the instrument panel
• Hard starting or extended cranking time, especially during cold starts
• Rough idle or irregular engine RPM fluctuations when the machine is warming up
• Cooling fan running continuously at high speed, even when the engine is cold
• Reduced engine power or failure to reach normal operating temperature, affecting hydraulic system efficiency

Potential Causes

The most common technical reasons for Code 122 on used SH210-6 excavators include:

• Failed ECT sensor due to internal element degradation or contamination from coolant additives
• Damaged wiring harness between the sensor and ECM, particularly at rub points near the engine block or frame rails
• Corroded or loose electrical connectors at the sensor plug—common in machines with high operating hours
• Faulty ECM with damaged input circuits (rare, but possible in older units)
• Low coolant level causing sensor exposure to air instead of liquid coolant
• Incorrect sensor replacement with non-OEM parts having different resistance specifications

How to Troubleshoot and Fix Code 122

Step 1: Visual Inspection Begin by checking the coolant level in the radiator and overflow tank. On used excavators, inspect the ECT sensor connector located on the engine block (typically near the thermostat housing) for corrosion, moisture, or damaged pins. Examine the wiring harness for chafing, cuts, or signs of previous repairs.

Step 2: Sensor Resistance Test Disconnect the ECT sensor connector and use a digital multimeter set to ohms. Measure resistance across the sensor terminals. At 68°F (20°C), resistance should typically read between 2,000-3,000 ohms (consult your service manual for exact specifications). Compare readings at different temperatures—resistance should decrease as temperature increases.

Step 3: Circuit Voltage Check With the sensor disconnected and ignition ON (engine OFF), measure voltage at the ECM-side harness connector. You should see approximately 5 volts reference voltage. If voltage is absent or incorrect, trace the signal wire and ground wire back to the ECM for shorts or opens.

Step 4: Replacement and Verification If the sensor fails testing, replace it with an OEM-equivalent ECT sensor designed for Sumitomo applications. Before installation, apply dielectric grease to connector terminals to prevent future corrosion—critical for used machines operating in harsh environments. Clear the fault code using diagnostic software or by disconnecting the battery, then monitor for code recurrence during a complete warm-up cycle.

Disclaimer: This guide provides general troubleshooting information. Always consult your Sumitomo service manual and consider professional diagnostic assistance for complex electrical issues or if you're unfamiliar with excavator systems.