Sumitomo SH80-6B Fault Code P0118-3: Complete Diagnostic Guide

What is Sumitomo SH80-6B Fault Code P0118-3?

Fault Code P0118-3 indicates an Engine Coolant Temperature (ECT) Sensor Circuit High Voltage condition on the Sumitomo SH80-6B excavator. This code triggers when the Engine Control Module (ECM) detects a voltage signal 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 SH80-6B's diesel 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 emission system operation. When the ECM receives abnormally high voltage readings, it cannot accurately determine engine temperature, potentially leading to improper fuel delivery, overheating protection failures, and reduced engine performance.

Common Symptoms

When P0118-3 is active on your Sumitomo SH80-6B, operators typically experience:

• Check Engine Light or malfunction indicator lamp illuminated on the dashboard
• Engine starting in "cold start mode" continuously, causing rough idling and excessive fuel consumption
• Engine derate or power reduction as the ECM enters protective mode
• Difficulty starting in cold weather conditions due to incorrect fuel mapping
• Radiator cooling fan running constantly at high speed, even when engine is cold

Potential Causes

The most common technical failures causing P0118-3 on used SH80-6B excavators include:

• Open circuit in the ECT sensor wiring harness, often caused by wire chafing near the engine block mounting points
• Failed coolant temperature sensor with internal resistance breakdown (common after 3,000+ operating hours)
• Corroded or loose electrical connectors at the sensor or ECM terminals
• Damaged sensor ground wire or poor ground connection to the engine block
• ECM internal fault (less common, but possible in high-hour machines)
• Previous repair attempts using incorrect sensor specifications or non-OEM parts

How to Troubleshoot and Fix Code P0118-3

Step 1: Visual Inspection Begin with a thorough inspection of the ECT sensor location (typically near the thermostat housing on the cylinder head). Check for damaged wiring, melted insulation from exhaust heat exposure, or corroded connectors. On used excavators, pay special attention to harness routing where wires contact metal surfaces—a common wear point on the SH80-6B.

Step 2: Electrical Testing Using a digital multimeter, disconnect the ECT sensor connector and measure resistance across the sensor terminals. At room temperature (68°F/20°C), resistance should read approximately 2,000-3,000 ohms. Next, check for voltage supply at the harness connector with ignition ON—you should see approximately 5 volts reference voltage from the ECM.

Step 3: Signal Wire Testing Measure resistance between the signal wire and ground with the sensor disconnected. Infinite resistance indicates proper insulation; low resistance suggests a short to ground. Also verify ground circuit continuity from the sensor ground terminal to the engine block (should be less than 1 ohm).

Step 4: Component Replacement If testing confirms sensor failure, replace with an OEM-equivalent ECT sensor matching Sumitomo specifications. Clean connector terminals with electrical contact cleaner and apply dielectric grease to prevent future corrosion. After installation, clear the fault code using diagnostic software and monitor for recurrence during a complete heat cycle.

Critical for Used Equipment: Before replacing the ECM (expensive), always verify wiring harness integrity throughout its entire length, as vibration damage and age-related insulation breakdown are far more common than ECM failure on older SH80-6B models.

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Disclaimer: This guide provides general diagnostic information for Sumitomo SH80-6B excavators. Always consult the manufacturer's service manual and consider professional diagnostic services for complex electrical issues. Improper repairs may cause additional damage or safety hazards.