What is Kobelco SK135SR-2 Fault Code P0118?

Fault Code P0118 on the Kobelco SK135SR-2 excavator indicates an Engine Coolant Temperature (ECT) Sensor Circuit High Input voltage condition. This diagnostic trouble code triggers when the engine control module (ECM) detects an abnormally high voltage signal from the coolant temperature sensor, typically exceeding 4.5-4.9 volts for longer than a specified time threshold.

The ECT sensor is a critical input device for the Kobelco SK135SR-2's Hino J05E diesel engine management system. This thermistor-type sensor provides real-time coolant temperature data that directly influences fuel injection timing, idle speed control, and engine protection strategies. When the ECM receives unreliable temperature data due to P0118, the system defaults to a predetermined "limp mode" value, which can significantly impact performance, fuel efficiency, and potentially cause long-term engine damage if ignored.

Common Symptoms

• Check Engine Light or malfunction indicator lamp (MIL) illuminated on the instrument cluster
• Hard starting conditions, especially during cold weather, as the ECM cannot properly adjust fuel enrichment
• Poor engine performance including rough idle, hesitation during acceleration, or reduced power output
• Cooling fan running continuously at high speed, even when the engine is cold, due to ECM assuming overheating conditions
• Increased fuel consumption and black exhaust smoke from improper air-fuel mixture calculations

Potential Causes

On used Kobelco SK135SR-2 excavators, P0118 typically stems from age-related deterioration rather than component failure:

• Open circuit in ECT sensor wiring harness, particularly where the wire bundle routes near the engine block mounting points (known rub-through location on this model)
• Corroded or loose connector terminals at the ECT sensor plug, especially on machines with significant operating hours in wet/muddy conditions
• Failed ECT sensor with internal open circuit, though less common than wiring issues
• Damaged ECM ground connections or corroded ground strap between engine and chassis frame
• Coolant contamination causing sensor element degradation in older machines with deferred maintenance

How to Troubleshoot and Fix Code P0118

Step 1: Visual Inspection and Connector Check

Begin with the ECT sensor located on the thermostat housing of the Hino J05E engine. Disconnect the two-wire sensor connector and inspect both the sensor pins and harness terminals for corrosion, moisture, or bent contacts. On used excavators, this connector often accumulates dirt and experiences pin-back issues. Clean with electrical contact cleaner and verify positive terminal lock.

Step 2: Sensor Resistance Testing

Using a digital multimeter (DMM), measure resistance across the ECT sensor terminals with the sensor removed from the engine. At 68°F (20°C), resistance should read approximately 2,400-2,700 ohms. At 176°F (80°C), expect 300-330 ohms. Values outside this range or infinite resistance (open circuit) confirm sensor failure requiring replacement with genuine Kobelco part 8-97306917-0 or equivalent quality aftermarket component.

Step 3: Wiring Harness Continuity and Voltage Testing

With the sensor disconnected and ignition ON, measure voltage at the harness-side connector. You should see approximately 5 volts on the signal wire (reference voltage from ECM). If voltage reads near battery voltage (12V+), this confirms the high input condition. Check wiring continuity from the sensor connector back to ECM pins using wiring diagrams. Pay special attention to harness routing near exhaust manifold heat shields and engine mount brackets where abrasion and heat damage commonly occur on higher-hour machines.

Step 4: Ground Circuit Verification

Verify ECM ground integrity by measuring resistance between the ECT sensor ground circuit and chassis ground—should be less than 1 ohm. On used Kobelco excavators, corroded ground straps frequently cause voltage reference problems. Clean and tighten all engine-to-frame ground connections.

Step 5: Clear Code and Verification

After repairs, clear fault codes using Kobelco diagnostic software or an appropriate OBD-II scan tool compatible with J1939 protocols. Operate the machine through full warm-up cycle and monitor live ECT data to confirm sensor readings track appropriately from cold (around 2V) to operating temperature (approximately 0.5-1.0V).

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Disclaimer: This guide provides general troubleshooting information for the Kobelco SK135SR-2. Always consult the official service manual for your specific machine serial number and consider professional diagnosis for complex electrical issues. Improper repairs may lead to additional damage or safety hazards.