Kobelco SK135SRLC-2 Fault Code R164: Complete Diagnostic Guide

What is Kobelco SK135SRLC-2 Fault Code R164?

Fault Code R164 indicates a malfunction in the engine coolant temperature sensor circuit or an abnormal coolant temperature reading on the Kobelco SK135SRLC-2 excavator. This code triggers when the Engine Control Module (ECM) detects voltage signals outside the normal operating range from the coolant temperature sensor (typically 0.5-4.5V), or when sensor readings are implausible for current operating conditions.

This fault is critical because the ECM relies on accurate coolant temperature data to manage fuel injection timing, engine speed control, and protect against overheating. On used machines like the SK135SRLC-2, this sensor's accuracy directly affects engine performance, fuel efficiency, and prevents catastrophic thermal damage to the cylinder head and engine block.

Common Symptoms

When Code R164 is active on your Kobelco excavator, operators typically experience:

• Engine warning light illuminated on the instrument panel, often accompanied by a temperature gauge reading abnormally high or low
• Engine derate mode engagement, limiting maximum RPM to approximately 1,500-1,800 to prevent potential overheating damage
• Hard starting conditions, especially in cold weather, due to improper fuel delivery calculations
• Rough idle or poor throttle response as the ECM compensates for missing temperature data
• Cooling fan running continuously at maximum speed regardless of actual engine temperature

Potential Causes

The most common technical reasons for R164 on used SK135SRLC-2 excavators include:

• Faulty coolant temperature sensor due to internal element degradation (common after 5,000+ operating hours)
• Damaged wiring harness between the sensor and ECM, particularly at known rub points near the engine mount brackets and along the valve cover
• Corroded or loose connector terminals at the sensor plug—moisture intrusion is frequent in excavator applications
• ECM internal fault affecting the sensor circuit (rare but possible on high-hour machines)
• Coolant contamination causing sensor element coating or reduced thermal transfer
• Poor ground connection at the engine block ground strap, creating voltage reference issues

How to Troubleshoot and Fix Code R164

Step 1: Visual Inspection Begin by inspecting the coolant temperature sensor located on the engine block near the thermostat housing. Check the wiring harness for abrasion, cuts, or heat damage, especially where it routes near hot exhaust components. On used excavators, examine all connector pins for corrosion—a white or green residue indicates moisture intrusion requiring immediate cleaning or connector replacement.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure resistance across the sensor terminals. At 20°C (68°F), resistance should read approximately 2,000-3,000 ohms; at 80°C (176°F), approximately 300-400 ohms. Compare readings to Kobelco specifications. Test harness continuity from the sensor connector to the ECM—resistance should be less than 5 ohms with no shorts to ground.

Step 3: Voltage Reference Check With ignition on and sensor disconnected, measure voltage at the harness connector. You should see approximately 5V reference voltage from the ECM. If voltage is absent or incorrect, trace wiring for breaks or check ECM power supply circuits.

Step 4: Replacement and Verification If the sensor tests faulty, install a genuine Kobelco coolant temperature sensor (aftermarket sensors often have different resistance curves causing persistent codes). Before installation on used machines, clean the sensor bore thoroughly and apply anti-seize compound. After replacement, clear codes using Kobelco diagnostic software or a compatible scanner, run the engine through warm-up cycles, and verify the code doesn't return.

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Disclaimer: This guide provides general diagnostic information for Code R164. Excavator repair involves working with high-temperature cooling systems and electrical components. Always consult the official Kobelco service manual for your specific serial number, and consider professional diagnostic assistance if you're unfamiliar with electrical troubleshooting procedures.