What is Kobelco SK140LC-8 Fault Code P0117?

Fault Code P0117 indicates an Engine Coolant Temperature (ECT) Sensor Circuit Low Input signal detected by the Engine Control Module (ECM). This fault is triggered when the ECM receives a voltage reading from the coolant temperature sensor that falls below the manufacturer's specified threshold, typically indicating a short to ground or an open circuit condition.

On the Kobelco SK140LC-8 excavator, the ECT sensor plays a critical role in monitoring engine temperature and controlling fuel injection timing, idle speed adjustments, and cooling fan operation. The Isuzu engine powering this model relies on accurate temperature data to optimize combustion efficiency and prevent overheating. When P0117 sets, the ECM defaults to a pre-programmed "limp mode" temperature value, which can compromise performance, increase emissions, and potentially cause long-term engine damage if left unaddressed.

Common Symptoms

• Check Engine Light (CEL) or malfunction indicator illuminated on the instrument cluster
• Hard starting conditions, especially during cold weather operation
• Rough idling or erratic engine RPM fluctuations at startup
• Black smoke from the exhaust due to improper fuel-air mixture calculations
• Cooling fan running continuously at high speed, regardless of actual engine temperature
• Reduced hydraulic performance as the ECM limits engine power output to protect components

Potential Causes

The P0117 code on used Kobelco SK140LC-8 excavators typically stems from age-related electrical and sensor degradation:

• Failed ECT sensor with internal resistance breakdown (common after 5,000+ operating hours)
• Damaged or corroded wiring harness at connector terminals, especially near the thermostat housing where heat cycling causes brittleness
• Shorted sensor circuit to ground, often from harness rubbing against engine block mounting brackets (known issue on this model)
• Corroded or loose connector pins at the ECT sensor or ECM interface
• Defective ECM, though rare, can misread sensor voltage (typically after electrical system surges)
• Coolant contamination on sensor tip affecting resistance readings

How to Troubleshoot and Fix Code P0117

Step 1: Visual Inspection Locate the ECT sensor on the engine block near the thermostat housing. Inspect the wiring harness for visible damage, chafing against metal surfaces, or coolant leaks that may cause corrosion. On used excavators, pay special attention to connector boots for cracking and check for green corrosion on pins—a common failure point after years of temperature cycling.

Step 2: Electrical Testing Disconnect the ECT sensor connector and use a digital multimeter to measure resistance across the sensor terminals. At 68°F (20°C), resistance should read approximately 2,000-3,000 ohms (refer to Kobelco service manual for exact specifications). Test the wiring harness for continuity between the sensor connector and ECM using a multimeter—resistance should be less than 5 ohms. Check for shorts to ground by measuring resistance between each sensor wire and engine ground; it should read infinite (open circuit).

Step 3: Signal Voltage Check With the ignition on and sensor connected, back-probe the sensor connector using a multimeter to check reference voltage from the ECM—it should read approximately 5 volts. A reading of 0 volts or battery voltage indicates a wiring fault or ECM problem.

Step 4: Repair or Replace If sensor resistance is out of specification, replace the ECT sensor (part typically costs $30-$80). When replacing, apply fresh dielectric grease to connector terminals to prevent future corrosion. If wiring shows damage, repair using heat-shrink solder connectors rather than crimp splices, and reroute harness away from hot engine components using proper standoffs. For used machines, consider replacing the entire sensor-to-ECM harness section if corrosion is widespread.

Step 5: Clear Code and Verify After repairs, use Kobelco diagnostic software or a compatible OBD-II scanner to clear the fault code. Run the engine through several heat cycles while monitoring live coolant temperature data to confirm proper sensor operation and verify the code does not return.

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Disclaimer: This guide provides general troubleshooting information for the Kobelco SK140LC-8. Always consult the manufacturer's service manual for model-specific procedures and torque specifications. If you're uncomfortable performing electrical diagnostics, seek assistance from a certified heavy equipment technician to avoid damaging sensitive ECM components.