Kobelco SK135SRLC-2 Fault Code P0117: Complete Diagnostic Guide

What is Kobelco SK135SRLC-2 Fault Code P0117?

Fault Code P0117 indicates Engine Coolant Temperature (ECT) Sensor Circuit Low Input. This means the Engine Control Module (ECM) is receiving a voltage signal from the coolant temperature sensor that falls below the manufacturer's specified threshold, typically less than 0.3 volts.

The ECT sensor is critical for the Kobelco SK135SRLC-2's engine management system. It monitors coolant temperature and sends real-time data to the ECM, which then adjusts fuel injection timing, idle speed, and emission controls. When this sensor reports abnormally low temperatures (even when the engine is warm), the ECM cannot optimize performance, leading to inefficient combustion, increased emissions, and potential engine damage. For the Isuzu engine powering this excavator model, precise temperature monitoring is essential for maintaining proper diesel particulate filter (DPF) regeneration cycles and overall engine longevity.

Common Symptoms

• Check Engine Light or warning lamp illuminated on the instrument panel
• Hard starting or extended cranking time, especially in cold conditions
• Rough idle and unstable engine RPM when first started
• Black smoke from the exhaust due to overly rich fuel mixture
• Poor fuel economy as the ECM defaults to cold-start enrichment modes

Potential Causes

For used Kobelco SK135SRLC-2 excavators, P0117 typically results from age-related deterioration:

• Worn or damaged ECT sensor with internal circuit failure (common after 5,000+ operating hours)
• Corroded or loose connector pins at the sensor harness connection point
• Damaged wiring harness where cables contact the engine block near the thermostat housing (known rub point on this model)
• Shorted sensor ground wire due to insulation breakdown from heat cycling
• Failed ECM (rare, but possible in machines with electrical system damage history)
• Coolant contamination on sensor terminals causing false 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, especially where it routes along the engine valley. Check the connector for corrosion, bent pins, or coolant intrusion—common issues in used excavators operating in harsh environments.

Step 2: Electrical Testing Disconnect the sensor connector. Using a digital multimeter, measure resistance across the sensor terminals. At room temperature (68°F/20°C), resistance should read approximately 2,000-3,000 ohms. If the reading shows infinite resistance (open circuit) or near-zero ohms (short circuit), replace the sensor.

Step 3: Circuit Verification With the sensor disconnected, check voltage supply at the harness connector. You should measure approximately 5 volts on the signal wire with ignition on. Test ground continuity between the ground wire and chassis—resistance should be less than 1 ohm. For used machines, inspect harness routing for wear points and apply protective loom if necessary.

Step 4: Clear and Retest After repairs, use Kobelco diagnostic software or a compatible OBD-II scanner to clear fault codes. Run the engine through warm-up cycles and monitor live ECT sensor data to confirm readings climb appropriately (typically reaching 180-200°F operating temperature).

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