Sumitomo SH260LC-6 Fault Code 685: Complete Diagnostic Guide

What is Sumitomo SH260LC-6 Fault Code 685?

Fault Code 685 indicates a Main Pump Pressure Sensor Circuit Malfunction in the Sumitomo SH260LC-6 excavator's hydraulic control system. This code is triggered when the Electronic Control Module (ECM) detects an abnormal voltage signal from the main pump pressure sensor, which monitors hydraulic system pressure to optimize pump output and prevent system damage.

The main pump pressure sensor is critical for this machine's load-sensing hydraulic system. It provides real-time pressure data that allows the ECM to adjust pump displacement for maximum efficiency. When this sensor circuit fails, the excavator loses its ability to modulate hydraulic power properly, resulting in reduced performance and potential component stress. For used SH260LC-6 models, this code often appears due to sensor degradation or wiring harness damage from years of vibration and exposure.

Common Symptoms

• Hydraulic system operating in default/limp mode with noticeably reduced digging force and slower cycle times
• Main monitor panel displaying the fault code with possible amber warning light activation
• Inconsistent hydraulic response where attachment speed varies unpredictably during operation
• Engine RPM fluctuations during loaded operations as the ECM cannot properly match engine output to hydraulic demand
• Abnormal pump whining or cavitation noises due to improper pressure regulation

Potential Causes

The most common technical causes for Code 685 on used SH260LC-6 excavators include:

• Main pump pressure sensor internal failure (typical after 8,000+ operating hours due to constant pressure cycling)
• Damaged or corroded wiring harness at the sensor connector, especially where the harness routes near the pump housing and experiences heat/vibration
• Connector pin corrosion or moisture intrusion at the 3-pin sensor connector beneath the pump access cover
• Chafed wiring at known rub points where the sensor harness contacts the main pump mounting bracket
• ECM voltage supply issues providing incorrect reference voltage (should be 5V ± 0.25V)
• Loose or damaged ground connections in the hydraulic system sensor circuit

How to Troubleshoot and Fix Code 685

Step 1: Visual Inspection and Connector Check Begin by accessing the main pump pressure sensor located on the main hydraulic pump body. Disconnect the 3-pin sensor connector and inspect for corrosion, bent pins, or moisture. On used excavators, this connector frequently shows green corrosion due to seal degradation. Clean contacts with electrical contact cleaner and apply dielectric grease.

Step 2: Sensor Circuit Testing Using a digital multimeter (DMM), check the sensor supply voltage at the harness connector (key on, engine off). You should measure 5V ± 0.25V on the reference pin. Next, measure sensor resistance across the signal and ground pins—specification is typically 250-350 ohms at room temperature. Values outside this range indicate sensor failure.

Step 3: Wiring Harness Continuity Check Trace the sensor harness from the pump to the main wiring harness junction near the hydraulic tank. Check for continuity between the sensor connector and ECM pins (consult service manual for pin assignments). Pay special attention to the harness routing near the pump mounting bracket—this is a known wear point on SH260LC-6 models where vibration causes insulation damage.

Step 4: Sensor Replacement and Calibration If testing confirms sensor failure, replace with a genuine Sumitomo pressure sensor (aftermarket sensors often have incorrect voltage curves). After installation, torque the sensor to 15-20 Nm and ensure the O-ring seal is properly seated. Clear the fault code using Sumitomo diagnostic software or a compatible scan tool, then perform a pressure calibration procedure as outlined in the service manual.

Critical Note for Used Excavators: Before replacing the sensor, thoroughly inspect all harness routing and secure any loose wiring with proper clamps. Check hydraulic oil condition—contaminated oil can accelerate sensor diaphragm failure.

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Disclaimer: This guide provides general diagnostic information for Sumitomo SH260LC-6 excavators. Hydraulic system repairs involve high-pressure components and specialized tools. Always consult the official Sumitomo service manual and consider professional diagnostic assistance if you're unfamiliar with hydraulic system troubleshooting. Improper repairs can result in equipment damage or personal injury.