What is Sumitomo SH480HD-6 Fault Code 1655?

Fault Code 1655 on the Sumitomo SH480HD-6 excavator indicates a Main Relief Valve Solenoid Circuit Malfunction, specifically detecting an abnormal electrical condition in the proportional pressure control solenoid that regulates the main hydraulic relief valve. This code is triggered when the Engine Control Module (ECM) detects voltage irregularities, open circuits, or short circuits in the solenoid's control circuit.

This fault is critical for the SH480HD-6 because the main relief valve solenoid directly controls maximum hydraulic system pressure. When this circuit malfunctions, the excavator cannot properly regulate hydraulic pressure across all functions, potentially causing erratic operation, reduced lifting capacity, or complete hydraulic system shutdown. The Isuzu engine-based ECM continuously monitors this circuit to prevent catastrophic hydraulic component damage.

Common Symptoms

• Hydraulic power loss or inconsistent boom/arm/bucket response during operation
• Engine derate mode activation, limiting RPM to 1,200-1,500 to protect the hydraulic system
• Warning light illumination on the instrument cluster, often accompanied by audible alarm
• Erratic hydraulic pressure causing jerky movements or unexpected speed variations in all functions
• Complete hydraulic function lockout in severe cases, rendering the machine inoperable

Potential Causes

The most common technical reasons for Code 1655 on used SH480HD-6 excavators include:

• Faulty main relief valve solenoid due to internal coil failure or contamination from hydraulic fluid ingress
• Damaged wiring harness at known rub points near the hydraulic pump area where harnesses contact the rotating components
• Corroded or loose electrical connectors at the solenoid or ECM interface, common in machines with 5,000+ operating hours
• ECM internal driver circuit failure affecting the solenoid control output
• Voltage supply issues from the main power harness or ground connection degradation
• Contaminated hydraulic oil causing solenoid valve sticking and increased current draw

How to Troubleshoot and Fix Code 1655

Step 1: Visual Inspection Begin by locating the main relief valve solenoid on the main hydraulic pump assembly. Inspect the electrical connector for corrosion, bent pins, or oil contamination. On used excavators, check the wiring harness routing for abrasion points where it contacts metal surfaces—this is a known failure point on SH480HD-6 models.

Step 2: Electrical Testing Using a digital multimeter, disconnect the solenoid connector and measure coil resistance across the solenoid terminals. Specifications typically range from 8-12 ohms at room temperature. Next, check for supply voltage (typically 12V or 24V depending on system) at the harness connector with the ignition on. Verify ground continuity with less than 1 ohm resistance.

Step 3: Circuit Testing With the harness connected but solenoid disconnected, use Sumitomo diagnostic software (or compatible tools like Jaltest) to command the solenoid on/off while monitoring circuit voltage. Look for voltage drops exceeding 0.5V indicating high resistance connections. Inspect the ECM connector pins for corrosion—pin-back probing may be necessary.

Step 4: Component Replacement If the solenoid tests outside specifications or shows internal contamination, replace it with a genuine Sumitomo or OEM-equivalent part. Before installation on used machines, flush the hydraulic oil filter and inspect for metal contamination that may have damaged the old solenoid. Always apply dielectric grease to connectors during reassembly to prevent future corrosion.

Step 5: System Verification Clear the fault code using diagnostic software, then operate the excavator through all hydraulic functions under load. Monitor for code recurrence and verify proper hydraulic pressure using a test gauge at the main relief valve test port (typical specification: 320-350 bar).

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Disclaimer: This guide provides general troubleshooting information. Always consult the official Sumitomo SH480HD-6 service manual and consider professional diagnostic services for complex electrical issues. Hydraulic system work requires proper training and safety precautions.