Sumitomo SH210-6 Fault Code 1655: Technical Guide

What is Sumitomo SH210-6 Fault Code 1655?

Fault Code 1655 on the Sumitomo SH210-6 excavator indicates a malfunction in the Pilot Pressure Sensor Circuit, specifically detecting an abnormal voltage signal or open circuit condition within the pilot hydraulic system monitoring network. This code is generated when the Engine Control Module (ECM) or Main Controller detects voltage readings outside the acceptable range (typically 0.5-4.5V) from the pilot pressure sensor, which monitors the pilot hydraulic pressure used to operate the machine's control levers.

This fault is critical for the SH210-6 because the pilot pressure sensor provides essential feedback to the controller about operator input commands. Without accurate pilot pressure readings, the excavator's proportional control system cannot properly modulate hydraulic flow, potentially resulting in erratic boom, arm, or bucket movements. For used machines, this sensor circuit is particularly vulnerable due to years of vibration, moisture exposure, and connector corrosion common in construction environments.

Common Symptoms

• Warning lamp illuminated on the instrument cluster (typically a hydraulic system warning or check engine light)
• Sluggish or unresponsive hydraulic controls, particularly affecting fine control movements
• Intermittent loss of proportional control, where joystick inputs don't match expected machine response
• Engine derate mode may activate on some SH210-6 units, limiting RPM to protect the hydraulic system
• Erratic swing or travel functions when attempting simultaneous multi-function operations

Potential Causes

The most common causes of Code 1655 on used Sumitomo SH210-6 excavators include:

• Failed pilot pressure sensor due to internal diaphragm rupture or electronic component degradation (common after 8,000+ operating hours)
• Corroded or moisture-contaminated connectors at the sensor harness connection point near the pilot valve block
• Damaged wiring harness with particular wear points where the harness routes along the upper structure near the cab mounting area
• Poor ground connection at the sensor or controller ground points, often caused by paint buildup or rust on mounting surfaces
• ECM/Controller internal fault (less common but possible on high-hour machines with voltage spike history)
• Contaminated pilot hydraulic oil causing sensor membrane failure or pressure port blockage

How to Troubleshoot and Fix Code 1655

Step 1: Visual Inspection and Connector Check Begin by locating the pilot pressure sensor mounted on the pilot valve block (typically under the operator's seat area). Disconnect the sensor's electrical connector and inspect for corrosion, bent pins, or moisture intrusion. Clean contacts with electrical contact cleaner and check for proper pin tension. On used excavators, this connector often shows green corrosion due to years of humidity exposure.

Step 2: Sensor Circuit Voltage Testing Using a digital multimeter (DMM), perform voltage checks with the ignition on but engine off. Backprobe the sensor connector to measure supply voltage (should read approximately 5V on the supply wire). Check the signal wire voltage with the sensor connected during normal pilot pressure application—readings should vary smoothly between 0.5-4.5V as you move control levers. Any reading stuck at 0V, 5V, or fluctuating erratically indicates sensor failure or wiring issues.

Step 3: Resistance and Ground Path Testing With the sensor disconnected and ignition off, measure resistance between sensor terminals (consult service manual for specifications, typically 200-500 ohms for internal resistance). Test continuity from sensor ground to chassis ground—resistance should be less than 1 ohm. Check wiring harness for shorts to ground or power by measuring resistance between signal wire and ground/power with harness disconnected at both ends.

Step 4: Physical Sensor and Hydraulic System Check Remove the pilot pressure sensor and inspect the pressure port for contamination or debris. Check pilot hydraulic oil condition—milky appearance indicates water contamination that can damage sensors. Verify pilot system pressure using a mechanical pressure gauge (should be 3.5-4.0 kg/cm² at idle). For used machines, replace the pilot filter if service history is unknown, as contamination is a common root cause.

Step 5: Component Replacement and Verification If testing confirms sensor failure, replace with a genuine Sumitomo part or verified OEM equivalent—aftermarket sensors often cause repeat failures on this model. After replacement, clear fault codes using Sumitomo diagnostic software or by disconnecting the battery negative terminal for 5 minutes. Test operate all functions through full range and verify code doesn't return. On high-hour used machines, consider replacing the entire sensor harness section if wires show brittleness or insulation cracking.

Disclaimer: This guide provides general troubleshooting information for experienced technicians. Always consult the official Sumitomo service manual for your specific serial number range and torque specifications. If you lack proper diagnostic tools or experience with hydraulic systems, consult a certified Sumitomo dealer or qualified heavy equipment technician to prevent injury or further machine damage.