What is Sumitomo Excavator Fault Code P0117?

Fault Code P0117 indicates an Engine Coolant Temperature (ECT) Sensor Circuit Low Input voltage condition. This diagnostic trouble code (DTC) is triggered when the Engine Control Module (ECM) detects that the voltage signal from the coolant temperature sensor has fallen below the manufacturer's specified threshold, typically below 0.14 volts.

In Sumitomo excavators, the ECT sensor plays a critical role in monitoring engine operating temperature and feeding this data to the ECM. The ECM uses this information to adjust fuel injection timing, air-fuel mixture, idle speed, and cooling fan operation. When P0117 is active, the ECM cannot accurately gauge engine temperature, potentially causing the system to default to fail-safe mode, which can significantly impact machine performance and fuel efficiency.

Common Symptoms

When fault code P0117 is active on your Sumitomo excavator, you may experience:

• Check Engine Light or malfunction indicator lamp illuminated on the instrument cluster
• Hard starting or extended cranking time, especially when the engine is cold
• Rough idle and unstable engine RPM during warm-up periods
• Poor fuel economy due to the ECM defaulting to enriched fuel maps
• Black smoke from the exhaust during initial startup or operation
• Engine derate or reduced power output as a protective measure

Potential Causes

Several technical failures can trigger P0117 on used Sumitomo excavators:

• Faulty ECT sensor with internal resistance breakdown or element failure (most common in machines with 5,000+ operating hours)
• Damaged or corroded wiring harness between the sensor and ECM, particularly at known rub points near the engine mount brackets
• Shorted sensor ground wire causing constant low voltage readings
• Corroded or loose connector terminals at the ECT sensor connection point, common in machines exposed to harsh environments
• Defective ECM (rare, but possible in older units or after electrical system surges)
• Coolant contamination on sensor terminals causing electrical pathway disruption

How to Troubleshoot and Fix Code P0117

Step 1: Visual Inspection Begin with a thorough physical inspection of the ECT sensor and its wiring harness. On used excavators, check for connector corrosion, damaged insulation, or wire chafing near moving engine components. Inspect coolant levels—low coolant can expose the sensor, causing erratic readings.

Step 2: Electrical Testing Using a digital multimeter (DMM), disconnect the ECT sensor connector and measure resistance across the sensor terminals. At room temperature (68°F/20°C), resistance should typically read 2,000-3,000 ohms (consult your Sumitomo service manual for exact specifications). If readings are out of range or show infinite resistance, replace the sensor.

Step 3: Circuit Verification Test the signal wire voltage at the ECM connector with the sensor disconnected. You should read approximately 5 volts reference voltage from the ECM. If voltage is absent, inspect for open circuits in the harness or ECM issues. Check continuity of the ground circuit to ensure proper sensor grounding.

Step 4: Advanced Diagnostics Connect Sumitomo diagnostic software or compatible scan tool to monitor live ECT sensor data. Compare actual coolant temperature (measured with an infrared thermometer) against sensor readings. Significant discrepancies confirm sensor failure. For used equipment, always inspect connector pins for bent or pushed-back terminals before parts replacement.

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Disclaimer: This guide provides general troubleshooting information. Always consult your Sumitomo service manual and consider professional diagnostic assistance for complex electrical issues or if you're unfamiliar with high-voltage systems.