What is Kobelco SK135SRLC-2 Fault Code P0118?

Fault Code P0118 indicates an Engine Coolant Temperature (ECT) Sensor Circuit High Input condition. This means the Engine Control Module (ECM) is receiving a voltage signal from the coolant temperature sensor that is abnormally high, typically above 4.9 volts, suggesting either an open circuit, faulty sensor, or wiring issue.

In the Kobelco SK135SRLC-2 excavator, the ECT sensor plays a critical role in engine management by monitoring coolant temperature and sending data to the ECM. This information directly affects fuel injection timing, idle speed control, and engine warm-up procedures. When P0118 triggers, the ECM typically defaults to a preset temperature value, which can lead to inefficient combustion, increased emissions, and potential engine damage if ignored.

Common Symptoms

When P0118 is active on your SK135SRLC-2, you may experience:

• Check Engine Light or malfunction indicator lamp illuminated on the dashboard
• Difficulty starting the engine, especially when cold, or prolonged cranking times
• Rough idle and poor engine performance during warm-up phase
• Excessive fuel consumption due to the ECM operating in failsafe mode with incorrect temperature assumptions
• Black smoke from exhaust during operation, indicating overly rich fuel mixture

Potential Causes

The most common technical reasons for P0118 appearing on used Kobelco excavators include:

• Faulty ECT sensor with internal circuit failure or contamination from aged coolant
• Open circuit or broken wiring in the sensor harness, particularly at flex points near the engine block
• Corroded or loose connector pins at the ECT sensor plug—common in machines with high operating hours
• Damaged ECM or internal circuit board corrosion (rare but possible in older units)
• Coolant system issues causing sensor exposure to air pockets or insufficient coolant contact
• Harness chafing at known rub points where the sensor wire routes along the valve cover or near rotating components

How to Troubleshoot and Fix Code P0118

Step 1: Visual Inspection Begin by locating the ECT sensor on the engine block (typically near the thermostat housing). Inspect the sensor connector for corrosion, moisture, bent pins, or damage. On used excavators, pay special attention to harness wear at routing points where vibration or heat may have degraded the insulation.

Step 2: Electrical Testing Disconnect the ECT sensor connector. Using a digital multimeter, measure the resistance across the sensor terminals. At room temperature (68°F/20°C), resistance should typically read between 2,000-3,000 ohms depending on specifications. Compare your reading to Kobelco's service manual values. An infinite (open) reading confirms sensor failure.

Step 3: Circuit Voltage Check With the sensor disconnected and ignition on (engine off), measure voltage at the harness connector leading to the ECM. You should see approximately 5 volts reference voltage. If voltage reads near battery voltage (12V+) or zero, there's a wiring fault or ECM issue.

Step 4: Wiring Harness Inspection Trace the sensor wiring from connector to ECM, checking for breaks, shorts to ground, or shorts to power. In older SK135SRLC-2 machines, inspect areas where the harness passes near hot exhaust components or sharp edges that may have worn through insulation over time.

Step 5: Component Replacement If the sensor tests faulty, replace with a genuine or OEM-equivalent ECT sensor. Before installation, clean the sensor bore, apply appropriate thread sealant if required, and ensure proper torque specifications. After replacement, clear the fault code using Kobelco diagnostic software or a compatible scan tool and verify repair with a test run.

Disclaimer: This guide provides general troubleshooting information. Always consult the Kobelco SK135SRLC-2 service manual and consider professional diagnostic assistance for complex electrical issues or if you're unfamiliar with excavator systems.