What is Kobelco SK135SR-2 Fault Code P0117?

Fault Code P0117 on the Kobelco SK135SR-2 excavator indicates "Engine Coolant Temperature (ECT) Sensor Circuit Low Input." This diagnostic trouble code (DTC) is triggered when the Engine Control Module (ECM) detects a voltage signal from the coolant temperature sensor that is below the manufacturer's specified threshold, typically below 0.15-0.20 volts.

The ECT sensor is a critical component that monitors engine coolant temperature and sends real-time data to the ECM. This information directly influences fuel injection timing, idle speed control, and engine protection protocols. On the Kobelco SK135SR-2's diesel engine, accurate coolant temperature readings are essential for optimal combustion efficiency and preventing thermal damage. When P0117 activates, the ECM typically defaults to a predetermined "safe" temperature value, which can significantly affect engine performance and fuel economy.

Common Symptoms

When fault code P0117 is active on your SK135SR-2, operators may experience:

• Check Engine Light or malfunction indicator lamp illuminated on the instrument panel
• Hard starting or extended cranking time, especially in cold weather conditions
• Rough idle or hunting/surging engine RPM during warm-up phase
• Black smoke from exhaust due to overly rich fuel mixture
• Poor fuel economy as the ECM compensates for incorrect temperature data
• Engine derate mode activation in severe cases, limiting power output

Potential Causes

Several factors commonly trigger P0117 on used Kobelco excavators:

• Faulty ECT sensor with internal short circuit or degraded thermistor element
• Damaged wiring harness between sensor and ECM, particularly at flex points near the engine mount or cylinder head
• Corroded or loose connector at the sensor plug, especially on machines with coolant leak history
• Grounded signal wire due to harness chafing against engine components or frame
• Coolant contamination causing sensor element corrosion
• ECM internal fault (rare but possible on higher-hour machines)
• Low coolant level causing sensor exposure to air rather than coolant

How to Troubleshoot and Fix Code P0117

Step 1: Visual Inspection Begin with a thorough examination of the ECT sensor and its wiring. Located typically on the thermostat housing or cylinder head, inspect for coolant residue, corrosion on the connector pins, or physical damage. On used excavators, check the wire harness routing for rub points where insulation may be worn through from vibration.

Step 2: Sensor Resistance Testing Disconnect the ECT sensor connector and use a digital multimeter to measure resistance across the sensor terminals. At room temperature (68°F/20°C), resistance should typically read 2,000-3,000 ohms. Compare your reading with Kobelco specifications. A reading near zero ohms indicates an internal short circuit, confirming sensor failure.

Step 3: Circuit Voltage Check With the sensor disconnected and ignition ON (engine off), measure voltage at the harness connector. You should see approximately 5 volts on the signal wire (reference voltage from ECM). If voltage is absent or significantly low, trace the signal wire back to the ECM for breaks or shorts to ground.

Step 4: Connector Cleaning and Repair Clean connector terminals with electrical contact cleaner and inspect for bent pins or moisture intrusion. Apply dielectric grease before reconnecting to prevent future corrosion—critical for used machines operating in harsh environments.

Step 5: Component Replacement If diagnostics confirm sensor failure, replace with a genuine Kobelco ECT sensor or quality OEM equivalent. After installation, clear fault codes using Kobelco diagnostic software or a compatible scanner, then monitor for code reoccurrence during a complete warm-up cycle.

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Disclaimer: This guide provides general troubleshooting information. Always consult the Kobelco SK135SR-2 service manual for model-specific procedures and torque specifications. If unfamiliar with electrical diagnostics, seek assistance from a qualified diesel technician to prevent further damage to the machine's electronic systems.