Sumitomo SH220LC-6 Fault Code 122: Complete Diagnostic Guide

What is Sumitomo SH220LC-6 Fault Code 122?

Fault Code 122 on the Sumitomo SH220LC-6 excavator indicates a malfunction in the engine coolant temperature sensor circuit or an abnormal coolant temperature reading detected by the engine control module (ECM). This diagnostic trouble code (DTC) signals that the ECM is receiving either an out-of-range voltage signal or an implausible temperature reading from the coolant temperature sensor.

The coolant temperature sensor is critical for the SH220LC-6's engine management system, as it directly influences fuel injection timing, engine warm-up cycles, and protection protocols. When this sensor fails or sends incorrect data, the ECM cannot properly regulate engine performance, potentially leading to inefficient combustion, increased emissions, and inadequate engine protection against overheating.

Common Symptoms

When Code 122 is active on your Sumitomo SH220LC-6, you may experience:

• Engine warning light illuminated on the instrument cluster or dash panel
• Hard starting or extended cranking time, especially during cold starts
• Rough idle or irregular engine performance during warm-up phase
• Excessive black smoke from the exhaust due to improper fuel mixture
• Engine derate mode activating, limiting RPM and hydraulic performance to protect components

Potential Causes

Several factors can trigger Code 122 on used Sumitomo excavators:

• Faulty coolant temperature sensor due to age-related degradation or internal element failure
• Damaged wiring harness near the engine block where vibration and heat cause wire insulation breakdown
• Corroded or loose electrical connectors at the sensor or ECM connection points (common in machines exposed to harsh environments)
• Shorted or open circuits in the sensor wiring, particularly at known rub points along the valve cover
• Low coolant level causing sensor exposure and inaccurate readings
• Failed ECM (rare, but possible in high-hour used machines with electrical system stress)

How to Troubleshoot and Fix Code 122

Step 1: Visual Inspection Begin by checking the coolant level in the radiator and overflow tank. Inspect the coolant temperature sensor (typically located on the engine block or thermostat housing) for physical damage, coolant leaks, or corrosion on the electrical connector. On used excavators, carefully examine the wiring harness for signs of chafing, melting, or damage from engine heat or vibration.

Step 2: Electrical Testing Disconnect the coolant temperature sensor connector and use a digital multimeter to 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 wiring harness for continuity from the sensor connector to the ECM and check for shorts to ground. Measure supply voltage at the connector with the ignition on (should be approximately 5 volts).

Step 3: Component Replacement and Verification If the sensor reads out of specification or the wiring shows damage, replace the faulty component with OEM or quality aftermarket parts. For used machines, apply dielectric grease to all electrical connections to prevent future corrosion. Clear the fault code using Sumitomo diagnostic software or a compatible scan tool, then run the engine through multiple heat cycles to verify the repair.

Disclaimer: This guide provides general troubleshooting information. Always consult the official Sumitomo service manual for your specific machine serial number and consider professional diagnostic assistance for complex electrical issues.