What is Sumitomo SH220LC-6 Fault Code 73?

Fault Code 73 on the Sumitomo SH220LC-6 excavator indicates a malfunction in the main pump control system, specifically related to the pump discharge pressure sensor circuit or abnormal pressure readings. This code is triggered when the Electronic Control Unit (ECU) detects voltage irregularities, sensor failures, or hydraulic pressure values outside the manufacturer's specified operating range within the main hydraulic pump control system.

This fault is critical for the SH220LC-6 because the main pump discharge pressure sensor provides essential feedback to the ECU for regulating hydraulic flow and power distribution. When this system malfunctions, the excavator cannot properly modulate hydraulic pressure, directly impacting boom, arm, and swing functions. The Sumitomo SH220LC-6 relies on precise pressure monitoring to prevent pump damage and maintain optimal fuel efficiency across all hydraulic circuits.

Common Symptoms

When Code 73 is active on your SH220LC-6, operators typically experience:

• Erratic or sluggish hydraulic response across multiple functions, particularly during combined operations (boom + swing)
• Intermittent power loss or noticeable reduction in digging force and cycle times
• Warning light illumination on the instrument cluster, often accompanied by audible alarm
• Automatic engine derate or speed limitation to protect hydraulic components from damage
• Inconsistent hydraulic pressure causing jerky movements or delayed actuator response

Potential Causes

The most common technical reasons for Code 73 appearing on used SH220LC-6 excavators include:

• Pressure sensor failure due to internal component degradation or contaminated hydraulic fluid causing sensor membrane damage
• Wiring harness damage at known rub points near the main pump assembly where vibration causes insulation wear
• Corroded or loose electrical connectors at the sensor plug, especially on machines operating in wet or corrosive environments
• ECU calibration drift or software corruption in older control modules
• Actual hydraulic system problems including worn pump components, contaminated oil, or internal leakage affecting pressure readings
• Voltage supply issues from damaged power supply circuits or poor grounding connections

How to Troubleshoot and Fix Code 73

Step 1: Visual Inspection and Code Verification Connect a diagnostic scanner compatible with Sumitomo systems to confirm Code 73 is active and check for additional stored codes. Inspect the main pump discharge pressure sensor (located on the main hydraulic pump housing) for physical damage, oil contamination on connectors, or obvious wiring damage. On used excavators, carefully examine the entire wiring harness from the sensor to the ECU for chafing points where the harness contacts the frame or hydraulic lines.

Step 2: Electrical Testing Disconnect the pressure sensor connector and use a digital multimeter to check sensor resistance. Typical specifications for the SH220LC-6 pressure sensor range between 250-350 ohms (consult your service manual for exact values). Test supply voltage at the connector with ignition on; you should see approximately 5 volts. Check ground continuity between the sensor ground pin and chassis ground—resistance should be less than 1 ohm. Any deviation indicates wiring problems or sensor failure.

Step 3: Sensor and Hydraulic System Verification If electrical tests pass, the sensor itself may have failed internally. Replace the pressure sensor with a genuine Sumitomo part, as aftermarket sensors often cause recurring codes. Before reinstalling, check hydraulic oil condition—contaminated or degraded oil can damage new sensors. On high-hour used machines, consider testing actual pump discharge pressure with a mechanical gauge to verify the hydraulic system is generating correct pressure (typically 320-350 bar at rated RPM). If pressure is abnormal, internal pump wear may be the root cause rather than sensor failure.

Step 4: Final Verification After repairs, clear codes using your diagnostic tool, operate the machine through full work cycles, and monitor for code recurrence. Check connector sealing and apply dielectric grease to prevent moisture intrusion on used equipment.

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Disclaimer: This guide provides general troubleshooting information for Code 73 on Sumitomo SH220LC-6 excavators. Hydraulic systems operate under extreme pressure and require proper training and tools. Always consult the manufacturer's service manual and consider professional diagnostic assistance for complex electrical or hydraulic issues, especially on used machines with unknown service history.