Sumitomo SH210-6 Fault Code 638: Complete Diagnostic Guide

What is Sumitomo SH210-6 Fault Code 638?

Fault Code 638 on the Sumitomo SH210-6 excavator indicates a Swing Motor Pressure Sensor Circuit Malfunction. This diagnostic trouble code is triggered when the Electronic Control Module (ECM) detects an abnormal voltage signal from the swing motor pressure sensor, which monitors hydraulic pressure in the swing circuit.

The swing motor pressure sensor plays a critical role in the SH210-6's hydraulic management system. It continuously feeds pressure data to the ECM, allowing the controller to optimize swing speed, prevent overload conditions, and protect the swing motor from excessive pressure damage. When this sensor circuit fails, the excavator may enter a protective derate mode that limits swing function performance, directly impacting productivity on jobsites.

Common Symptoms

When Code 638 is active on your Sumitomo SH210-6, operators typically experience:

• Reduced swing speed or jerky, inconsistent swing rotation performance
• Warning light illuminated on the instrument cluster (typically the malfunction indicator)
• Swing function derate where the upper structure rotates slower than normal operating speed
• Intermittent loss of swing power, especially during high-demand operations
• ECM logging the fault in diagnostic memory, even if symptoms are intermittent

Potential Causes

The most common technical reasons for Code 638 on used SH210-6 excavators include:

• Pressure sensor internal failure due to age, contamination, or seal deterioration
• Wiring harness damage at known rub points near the swing bearing area where cables flex during rotation
• Connector corrosion on the sensor plug, especially on machines operating in wet or coastal environments
• Voltage supply issues from damaged wiring between the ECM and sensor (should read 5V reference)
• Hydraulic contamination causing sensor diaphragm damage or blockage
• ECM internal fault (rare, but possible on high-hour used machines)

How to Troubleshoot and Fix Code 638

Step 1: Visual Inspection Begin by locating the swing motor pressure sensor on the swing motor assembly. Inspect the sensor connector for corrosion, bent pins, or moisture intrusion. On used excavators, check the wiring harness routing for signs of chafing, especially where cables pass through the center joint to the upper structure.

Step 2: Electrical Testing Using a digital multimeter, check the sensor's voltage supply at the connector (key on, engine off). You should measure approximately 5 volts on the reference wire. With the sensor connected, measure the signal wire voltage—it should vary between 0.5-4.5V depending on pressure. An open circuit (no voltage) or constant 5V indicates sensor or wiring failure.

Step 3: Resistance Check Disconnect the sensor and measure resistance across the sensor terminals. Compare readings to Sumitomo specifications (typically 200-5000 ohms depending on temperature). Readings outside this range confirm sensor failure.

Step 4: Harness Continuity For used machines with high operating hours, perform a continuity test on all three wires (signal, reference, ground) from the ECM connector to the sensor connector. Repair any breaks or shorts to ground.

Step 5: Replacement and Verification If the sensor tests faulty, replace it with a genuine Sumitomo or OEM-equivalent part. After installation, clear codes using diagnostic software compatible with Sumitomo excavators, then cycle the swing function through full rotation to verify proper operation.

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Disclaimer: This guide provides general diagnostic procedures. Always consult the official Sumitomo SH210-6 service manual and consider professional assistance for complex electrical diagnostics or if you're unfamiliar with hydraulic system repairs.