Kobelco SK135SR-2 Fault Code R164: Complete Diagnostic Guide

What is Kobelco SK135SR-2 Fault Code R164?

Fault Code R164 indicates a malfunction in the swing motor secondary pressure sensor circuit. This code triggers when the Electronic Control Unit (ECU) detects an abnormal voltage signal or open/short circuit condition from the pressure sensor monitoring hydraulic pressure in the swing motor's secondary circuit.

The swing motor secondary pressure sensor is critical for the SK135SR-2's load-sensing hydraulic system. It provides real-time feedback to the ECU, enabling precise control of swing speed and preventing over-pressure conditions that could damage the swing machinery. When this sensor fails or its circuit is compromised, the excavator may enter a protective derate mode to prevent catastrophic hydraulic system damage.

Common Symptoms

When Code R164 is active on your Kobelco SK135SR-2, operators typically experience:

• Reduced swing speed or complete loss of swing function during operation
• Illuminated warning lamp on the instrument panel (typically amber maintenance light)
• Jerky or unresponsive swing movement when attempting rotation
• Intermittent swing performance that worsens as the machine warms up
• Fault code storage in ECU memory even after apparent normal operation resumes

Potential Causes

The most common technical reasons for R164 on used SK135SR-2 excavators include:

• Faulty swing motor secondary pressure sensor due to internal diaphragm failure or contamination from degraded hydraulic fluid
• Damaged wiring harness near the swing motor mounting area where cables experience continuous flexing and vibration
• Corroded or loose electrical connectors at the sensor plug (common in machines exposed to moisture or operated in coastal environments)
• ECU voltage supply issues affecting the 5-volt reference circuit to the sensor
• Hydraulic contamination causing sensor membrane degradation in high-hour used machines
• Chafed wires at known rub points near the upper structure rotating joint

How to Troubleshoot and Fix Code R164

Step 1: Visual Inspection Begin with a thorough examination of the swing motor pressure sensor and its wiring harness. On used excavators, focus on the harness routing from the sensor through the center joint where constant rotation causes wear. Look for abraded insulation, connector corrosion, or evidence of hydraulic fluid contamination on electrical connections.

Step 2: Electrical Testing Using a digital multimeter, check the sensor's supply voltage. You should measure approximately 5 volts DC at the sensor connector with the ignition on. Next, measure the signal wire voltage while monitoring swing motor pressure—it should vary between 0.5-4.5 volts proportionally with pressure changes. An open circuit (no voltage) or constant maximum voltage indicates sensor or wiring failure.

Step 3: Resistance and Continuity Checks Disconnect the sensor and measure resistance across its terminals (typically 200-500 ohms depending on specification). Check continuity from the sensor connector back to the ECU pins using wiring diagrams. On used machines, pay special attention to the ground circuit integrity, as corroded grounds are frequent culprits.

Step 4: Sensor Replacement and Calibration If testing confirms sensor failure, replace with a genuine Kobelco pressure sensor (part-specific to SK135SR-2). After installation, clear fault codes using Kobelco diagnostic software and perform a calibration cycle. Test swing function under varying loads to ensure proper operation.

Critical Note for Used Excavators: Before ordering expensive replacement sensors, thoroughly inspect connector pins for corrosion and harness routing for damage. Many R164 codes on high-hour machines resolve simply by cleaning connectors with electrical contact cleaner and re-routing chafed harnesses away from friction points.

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Disclaimer: This guide provides general troubleshooting information. Always consult the official Kobelco service manual for your specific machine serial number and consider professional diagnostic assistance for complex hydraulic-electrical issues. Improper repairs may void warranties or create safety hazards.