Kobelco SK135SRLC-2 Fault Code A035: Complete Diagnostic Guide

What is Kobelco SK135SRLC-2 Fault Code A035?

Fault Code A035 on the Kobelco SK135SRLC-2 excavator indicates a malfunction in the engine coolant temperature sensor circuit, specifically detecting an abnormal voltage signal or sensor out-of-range condition. This code is triggered when the ECM (Engine Control Module) receives voltage readings outside the expected parameters from the coolant temperature sensor, typically below 0.2V or above 4.8V.

The coolant temperature sensor plays a critical role in the Hino engine management system used in the SK135SRLC-2. The ECM relies on accurate temperature data to adjust fuel injection timing, control idle speed, and manage the cooling fan operation. When this sensor fails or provides incorrect data, engine performance, fuel efficiency, and component longevity can be significantly compromised.

Common Symptoms

When Code A035 is active, operators typically experience:

• Check engine light or malfunction indicator illuminated on the instrument panel
• Hard starting conditions, especially in cold weather, due to improper fuel enrichment
• Rough idle or unstable engine RPM when the machine first starts
• Cooling fan running continuously at high speed, regardless of actual engine temperature
• Black smoke from exhaust during warm-up due to incorrect fuel mixture calculations
• Possible engine derate or limited power output as a protective measure

Potential Causes

The most common technical reasons for Code A035 on used SK135SRLC-2 excavators include:

• Coolant temperature sensor failure due to age-related degradation or internal circuit breakdown
• Damaged wiring harness between the sensor and ECM, particularly at routing points near the engine block where heat and vibration cause insulation breakdown
• Corroded or loose connector terminals at the sensor connection point, common in machines exposed to harsh environments
• Shorted or open circuit in the sensor signal wire, often caused by harness chafing against frame components
• ECM internal fault (rare), where the temperature input circuit on the control module has failed
• Low coolant levels causing sensor exposure to air, resulting in false readings

How to Troubleshoot and Fix Code A035

Step 1: Visual Inspection Begin with a thorough inspection of the coolant temperature sensor located on the engine block (typically on the thermostat housing). Check for physical damage, coolant leaks around the sensor base, and verify the electrical connector is firmly seated. Inspect the wiring harness from the sensor back to the ECM for signs of abrasion, melting, or damage, paying special attention to areas where the harness contacts metal surfaces.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure its resistance at various temperatures. At 68°F (20°C), resistance should be approximately 2,000-3,000 ohms; at 176°F (80°C), it should drop to around 300-400 ohms. Next, check the signal voltage at the ECM connector with the sensor connected. With the ignition on and engine cold, you should read approximately 3.0-4.5V; as the engine warms, voltage should gradually decrease to 0.5-2.0V.

Step 3: Circuit and Component Verification Check for continuity in the signal wire between the sensor connector and ECM pin (consult the Kobelco service manual for specific pin locations). Verify there's no short to ground or short to power in the circuit. For used excavators, closely examine connector pins for corrosion or bent terminals—clean with electrical contact cleaner if necessary. If all electrical checks pass but the code persists, replace the coolant temperature sensor with an OEM or high-quality aftermarket unit and retest.

Step 4: Final Verification After repairs, clear the fault code using Kobelco diagnostic software or a compatible scan tool. Run the engine through a complete heat cycle (cold start to full operating temperature) while monitoring live sensor data. Verify the coolant temperature reading increases smoothly and matches actual engine temperature.

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Disclaimer: This guide provides general diagnostic information for Code A035. Always consult the official Kobelco service manual for your specific machine serial number. If you're uncomfortable performing electrical diagnostics, consult a certified Kobelco technician or qualified heavy equipment mechanic to prevent misdiagnosis or damage to electronic components.