Sumitomo SH350HD-5 Fault Code 1112: Technical Guide

What is Sumitomo SH350HD-5 Fault Code 1112?

Fault Code 1112 on the Sumitomo SH350HD-5 excavator indicates a malfunction in the Engine Coolant Temperature (ECT) Sensor circuit, specifically a high voltage signal detected by the Engine Control Module (ECM). This diagnostic trouble code is triggered when the ECM receives a voltage reading from the coolant temperature sensor that exceeds the manufacturer's specified range, typically above 4.8-5.0 volts.

The ECT sensor plays a critical role in the SH350HD-5's engine management system by monitoring coolant temperature and sending real-time data to the ECM. This information directly affects fuel injection timing, idle speed control, and engine protection protocols. When Code 1112 appears, the ECM cannot accurately determine engine temperature, potentially leading to improper fuel delivery, increased emissions, and risk of engine damage from overheating conditions.

Common Symptoms

When Code 1112 is active on your Sumitomo SH350HD-5, operators typically experience:

• Engine warning light illuminated on the instrument cluster, often accompanied by a temperature gauge reading abnormally low or at minimum
• Hard starting conditions, especially when the engine is warm, due to incorrect fuel mapping
• Rough idle or erratic engine performance as the ECM defaults to failsafe temperature values
• Cooling fan running continuously at maximum speed regardless of actual engine temperature
• Reduced engine power or derate mode activation to protect the engine from potential thermal damage

Potential Causes

Several technical factors commonly trigger Code 1112 on used SH350HD-5 excavators:

• Open circuit in the ECT sensor wiring harness, particularly where the harness routes near the engine block or exhaust manifold (known wear point on this model)
• Failed coolant temperature sensor with internal open circuit or degraded thermistor element
• Corroded or loose connector pins at the sensor connection point, especially on machines with extended hours in wet or corrosive environments
• Damaged ECM connector terminals or moisture intrusion in the engine control module
• Chafed wiring from improper harness routing during previous repairs or engine service work

How to Troubleshoot and Fix Code 1112

Step 1: Visual Inspection Begin with a thorough inspection of the ECT sensor and its wiring harness. Located on the engine block near the thermostat housing, check for physical damage, coolant leaks, or corrosion. On used excavators, pay special attention to harness routing where it contacts metal surfaces—vibration wear is common after 5,000+ operating hours.

Step 2: Electrical Testing Disconnect the ECT sensor connector and measure resistance across the sensor terminals using a digital multimeter. At room temperature (68°F/20°C), resistance should read approximately 2,000-3,000 ohms. Compare readings against Sumitomo's specification chart. Also check for continuity between sensor terminals and ground—any continuity indicates sensor failure.

Step 3: Wiring Harness Verification With the sensor disconnected, measure voltage at the harness connector. You should see approximately 5 volts on the signal wire with ignition on. If voltage reads 5V or higher with no load, the ECM and power supply circuit are functioning. Check for short circuits by measuring resistance between the signal wire and ground (should be infinite resistance).

Step 4: Connector and Ground Inspection For used machines, meticulously inspect connector terminals for corrosion, bent pins, or moisture. Clean connections with electrical contact cleaner and apply dielectric grease. Verify the sensor ground circuit has less than 0.5 ohms resistance to chassis ground.

Step 5: Component Replacement If testing confirms sensor failure, replace the ECT sensor using OEM or equivalent quality parts. After installation, clear the fault code using Sumitomo diagnostic software or a compatible J1939 scan tool and verify the code doesn't return after a complete heat cycle.

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Disclaimer: This guide provides general diagnostic information for Code 1112. Always consult the official Sumitomo SH350HD-5 service manual and consider professional diagnostic assistance for complex electrical issues. Improper repairs may cause additional damage or safety hazards.