What is Kobelco SK200-8 Fault Code P0118?

Fault Code P0118 on the Kobelco SK200-8 excavator indicates "Engine Coolant Temperature (ECT) Sensor Circuit High Input." This diagnostic trouble code (DTC) is triggered when the Engine Control Module (ECM) detects an abnormally high voltage signal from the coolant temperature sensor, typically exceeding 4.9 volts for more than 0.5 seconds.

The ECT sensor is a critical thermistor-type component that monitors engine coolant temperature and sends voltage signals to the ECM. On the SK200-8's Hino J05E engine, this sensor plays a vital role in controlling fuel injection timing, idle speed, and cooling fan activation. When the ECM receives an implausibly high voltage reading (indicating extremely cold temperatures or circuit failure), it defaults to a fixed temperature value and logs P0118, potentially causing poor engine performance and increased fuel consumption.

Common Symptoms

• Check Engine Light (CEL) illuminated on the instrument panel with fault code stored in ECM memory
• Hard starting or extended cranking time, especially in warm conditions, as the ECM incorrectly assumes the engine is cold
• Rough idle or engine stalling during warm-up periods due to incorrect fuel delivery calculations
• Black exhaust smoke from overfueling caused by the ECM's default cold-start enrichment mode
• Cooling fan running continuously or not activating properly, as thermal management systems rely on accurate temperature data

Potential Causes

The most common technical failures triggering P0118 on used SK200-8 excavators include:

• Open circuit in the ECT sensor wiring harness, often due to wire chafing near the engine valley where the harness routes close to the fuel injection pump
• Failed ECT sensor with internal open circuit (common failure mode after 6,000+ operating hours)
• Corroded or loose connector at the sensor terminal—moisture ingress is frequent in excavators operating in wet conditions
• Damaged ECM pins or internal ECM circuitry issues (rare but possible in machines with electrical system history)
• Broken sensor ground wire (typically a dedicated ground to the engine block that can corrode over time)

How to Troubleshoot and Fix Code P0118

Step 1: Visual Inspection Begin with a thorough inspection of the ECT sensor connector located on the engine's thermostat housing. Disconnect the 2-pin connector and check for corrosion, bent pins, or moisture. On used excavators, this connector often shows green corrosion from coolant vapor exposure. Clean contacts with electrical contact cleaner and inspect the wiring harness for abrasion points where it contacts the engine block or fuel lines.

Step 2: Sensor Resistance Testing Using a digital multimeter (DMM), measure the resistance across the ECT sensor terminals with the sensor disconnected. At 68°F (20°C), resistance should read approximately 2,200-2,800 ohms. At 176°F (80°C), it should drop to 200-400 ohms. Readings showing infinite resistance (open circuit) or significantly outside specifications indicate a failed sensor requiring replacement (Kobelco part number YN01V00037F1).

Step 3: Circuit Voltage Testing With the ignition on and sensor disconnected, back-probe the harness connector and measure voltage between the signal wire (typically the darker wire) and ground. You should read approximately 5 volts (the ECM's reference voltage). If voltage is present, the wiring and ECM are functional, confirming sensor failure. If no voltage is present, trace the harness for breaks or shorts back to the ECM, paying special attention to harness routing near sharp edges.

Step 4: Verify Repair After replacing the sensor or repairing wiring, clear the fault code using Kobelco diagnostic software or a compatible scanner. Operate the machine through a full warm-up cycle and monitor live coolant temperature data to ensure readings climb smoothly from ambient to operating temperature (approximately 180-195°F).

Disclaimer: This guide provides general diagnostic information for experienced technicians. Always consult the Kobelco SK200-8 service manual for model-specific procedures and torque specifications. If you're unfamiliar with electrical diagnostics or working on high-pressure cooling systems, seek assistance from a certified Kobelco technician or qualified heavy equipment mechanic.