What is Hitachi ZX350LCK-5G Fault Code 11304-4?

Fault Code 11304-4 on the Hitachi ZX350LCK-5G indicates a malfunction in the hydraulic pump solenoid proportional valve circuit, specifically detecting an open circuit or abnormal voltage signal in the main pump control system. This code is generated when the ECM (Engine Control Module) detects that the electrical current or voltage supplied to the hydraulic pump's proportional solenoid valve falls outside the manufacturer's specified range.

This fault is critical because the proportional solenoid valve directly controls hydraulic pump output based on operator demand and load conditions. On the ZX350LCK-5G, this valve regulates fuel efficiency and hydraulic response by adjusting pump displacement. When this circuit fails, the excavator may default to a fixed displacement mode or enter derate mode, significantly reducing productivity and potentially causing hydraulic system damage due to improper pressure regulation.

Common Symptoms

• Hydraulic sluggishness or complete loss of auxiliary hydraulic functions (boom, arm, bucket movements become slow or unresponsive)
• Engine derate or automatic power reduction, limiting machine performance to protect the hydraulic system
• Warning light illuminated on the instrument cluster, often accompanied by continuous audible alarms
• Erratic pump noise or unusual whining sounds from the main hydraulic pumps during operation
• Increased fuel consumption as the system fails to optimize pump output based on load requirements

Potential Causes

The most common technical causes for Code 11304-4 on used ZX350LCK-5G excavators include:

• Damaged or corroded wiring harness at known rub points near the hydraulic pump mounting area where vibration causes insulation wear
• Failed proportional solenoid valve due to internal coil breakdown or contaminated hydraulic fluid causing mechanical seizure
• Loose or corroded electrical connectors at the solenoid valve connection point, particularly on machines operating in wet or corrosive environments
• ECM internal fault or software corruption (less common but possible on high-hour used machines)
• Voltage supply issues from the main power harness, including poor grounding connections or damaged power distribution modules

How to Troubleshoot and Fix Code 11304-4

Step 1: Visual Inspection and Connector Check Begin by disconnecting the battery and inspecting the proportional solenoid valve connector located on the main hydraulic pump. Look for corrosion, bent pins, moisture intrusion, or oil contamination on used excavators. Clean connectors with electrical contact cleaner and check for proper pin seating.

Step 2: Electrical Resistance and Voltage Testing Using a digital multimeter, measure the solenoid coil resistance at the valve connector (typically 8-12 ohms for Hitachi proportional valves—consult service manual for exact specifications). Then check for supply voltage (usually 12-24V) from the ECM harness with ignition on. No voltage indicates a harness break or ECM fault.

Step 3: Harness Continuity and Insulation Test Trace the wiring harness from the solenoid back to the ECM connector, checking for breaks, chafing, or shorts to ground. On used machines, pay special attention to areas where the harness routes near sharp edges or moving components. Use the multimeter's continuity function to verify circuit integrity.

Step 4: Component Replacement and Verification If resistance is out of specification or the solenoid shows physical damage, replace the proportional solenoid valve assembly. After replacement, clear fault codes using Hitachi Dr.EX diagnostic software or compatible scan tool, then perform a function test under load. Monitor for code recurrence over several operating hours.

Disclaimer: This guide provides general troubleshooting information. Always consult the official Hitachi service manual for your specific machine serial number and consider professional diagnostic services for complex electrical issues, especially on used equipment with unknown maintenance history.