Sumitomo SH350HD-6 Fault Code 112: Complete Diagnostic Guide

What is Sumitomo SH350HD-6 Fault Code 112?

Fault Code 112 on the Sumitomo SH350HD-6 excavator indicates an Engine Coolant Temperature (ECT) Sensor Circuit High Voltage condition. This diagnostic trouble code is triggered when the Engine Control Module (ECM) detects an abnormally high voltage signal from the coolant temperature sensor circuit, typically above 4.8-4.9 volts.

The ECT sensor plays a critical role in the SH350HD-6's engine management system by monitoring coolant temperature and sending this data to the ECM. This information directly affects fuel injection timing, idle speed control, and engine protection protocols. When Code 112 activates, the ECM cannot accurately determine engine temperature, potentially leading to improper fuel delivery, overheating risks, and reduced machine performance.

Common Symptoms

When Code 112 is active on your Sumitomo SH350HD-6, you may experience:

• Check Engine Light or malfunction indicator lamp illuminated on the instrument panel
• Engine running in default/limp mode with the ECM assuming a fixed coolant temperature value (typically 176°F/80°C)
• Hard starting conditions, especially during cold weather operation
• Rough idle or irregular engine RPM fluctuations
• Cooling fan running continuously at high speed regardless of actual engine temperature
• Potential engine derate or power reduction to protect components from assumed overheating

Potential Causes

Several technical issues commonly trigger Code 112 on used SH350HD-6 excavators:

• Open circuit in the ECT sensor wiring harness, often caused by wire breakage or connector separation
• Damaged or corroded connectors at the sensor or ECM connection points (common in machines with high operating hours)
• Failed ECT sensor with internal open circuit condition
• Harness chafing near engine mounting points or along the valve cover where vibration causes insulation wear
• ECM ground circuit failure affecting sensor reference voltage
• Moisture intrusion into sensor connector causing intermittent high resistance (prevalent in used machines operated in wet conditions)

How to Troubleshoot and Fix Code 112

Step 1: Visual Inspection Begin by inspecting the ECT sensor connector located near the thermostat housing on the engine block. Check for corrosion, bent pins, moisture, or damaged seals. On used excavators, examine the wiring harness routing from sensor to ECM for obvious damage, particularly where the harness contacts the engine or frame. Look for rubbed insulation, burned wires, or oil contamination that can degrade wire integrity.

Step 2: Electrical Testing Using a digital multimeter (DMM), disconnect the ECT sensor connector and measure resistance across the sensor terminals. A properly functioning sensor should read approximately 2,000-3,000 ohms at 68°F (20°C). An open circuit (infinite resistance) confirms sensor failure. Next, check the harness voltage with ignition on, engine off: you should see approximately 5 volts on the signal wire, indicating proper ECM reference voltage supply.

Step 3: Circuit Continuity and Repair Test continuity from the sensor connector through to the ECM connector using wiring diagrams specific to the SH350HD-6. Check for opens in both the signal wire and sensor ground circuit. For used machines, pay special attention to connector terminals—corrosion creates high resistance that mimics open circuits. Clean all connections with electrical contact cleaner and apply dielectric grease before reassembly.

Step 4: Component Replacement and Verification If the sensor tests faulty, replace with a genuine Sumitomo or OEM-equivalent ECT sensor and torque to specifications (typically 8-12 ft-lbs). After repairs, clear fault codes using diagnostic software compatible with Sumitomo excavators and perform a test cycle. Monitor live data to confirm the ECM receives proper temperature readings (voltage should decrease as temperature rises).

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Disclaimer: This guide provides general troubleshooting information for experienced technicians. Always consult the official Sumitomo service manual for your specific machine serial number. If unfamiliar with electrical diagnostics or working on high-value equipment, seek assistance from a certified Sumitomo dealer or qualified heavy equipment technician.