What is Hitachi ZX240-3 Fault Code 108-4?

Fault Code 108-4 on the Hitachi ZX240-3 excavator indicates a "Pump Discharge Pressure Sensor Circuit - Voltage Below Normal or Shorted to Low Source." This diagnostic trouble code (DTC) is triggered when the Engine Control Module (ECM) detects an abnormally low voltage signal from the hydraulic pump discharge pressure sensor, typically below the manufacturer's specified threshold of approximately 0.5 volts.

This sensor plays a critical role in monitoring the main hydraulic pump's output pressure, allowing the ECM to optimize engine load, fuel efficiency, and hydraulic performance. When this circuit malfunctions, the ZX240-3's electronic control system cannot accurately regulate pump displacement or implement load-sensing functions, potentially leading to reduced machine productivity and increased fuel consumption.

Common Symptoms

When Code 108-4 is active on your Hitachi ZX240-3, operators typically experience:

• Illuminated warning light on the instrument cluster, often accompanied by a diagnostic message display
• Reduced hydraulic power or sluggish boom/arm/bucket response during operation
• Engine derating or automatic power reduction as the ECM enters a protective mode
• Inconsistent hydraulic performance, particularly during high-demand operations like digging or lifting
• Increased fuel consumption due to improper pump control and inefficient engine-hydraulic matching

Potential Causes

The most common technical causes for Code 108-4 on used ZX240-3 excavators include:

• Damaged or corroded sensor connector at the pump discharge pressure sensor (common failure point due to hydraulic oil mist exposure)
• Broken or chafed wiring harness between the sensor and ECM, especially near routing points around the hydraulic pump or engine mounting brackets
• Failed pump discharge pressure sensor itself, with internal circuit degradation (typical after 5,000+ operating hours)
• Shorted sensor ground wire due to harness rubbing against frame components or hydraulic lines
• ECM internal circuit failure (less common but possible in high-hour machines)
• Corroded or loose ground connections at the main chassis ground points specific to the hydraulic system sensors

How to Troubleshoot and Fix Code 108-4

Step 1: Visual Inspection of Sensor and Harness

Begin by locating the pump discharge pressure sensor on the main hydraulic pump assembly. Thoroughly inspect the sensor connector for corrosion, bent pins, hydraulic oil contamination, or moisture intrusion. On used excavators, this connector frequently develops corrosion due to its proximity to hydraulic components. Check the wiring harness routing from the sensor to the ECM for obvious damage, chafing points against metal edges, or heat damage from nearby exhaust components.

Step 2: Electrical Testing with Multimeter

Disconnect the sensor connector and use a digital multimeter to measure resistance across the sensor terminals. The typical specification for a Hitachi pressure sensor is 250-350 ohms at room temperature (consult your service manual for exact values). Next, check for continuity in the wiring harness from the sensor connector back to the ECM connector pins. Measure voltage supply at the sensor connector with the ignition on—you should see approximately 5 volts DC on the supply wire. Any reading below 4.5 volts or above 5.5 volts indicates a power supply issue.

Step 3: Ground Circuit and Sensor Replacement

Check the sensor ground circuit for resistance; it should read less than 5 ohms to chassis ground. On used ZX240-3 machines, corrosion at ground points near the hydraulic tank is common. Clean all ground connections thoroughly with a wire brush and apply dielectric grease. If all electrical tests pass but the code persists, replace the pump discharge pressure sensor with a genuine Hitachi or OEM-equivalent part. After replacement, clear the fault code using Hitachi Dr.EX diagnostic software or a compatible scan tool and perform a test cycle under load.

Critical Note for Used Equipment: Before replacing the sensor, always inspect for harness wear patterns specific to the ZX240-3, particularly where the harness passes over the hydraulic pump mounting bracket. This known rub point can cause intermittent shorts that mimic sensor failure.

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Disclaimer: This guide provides general troubleshooting information for educational purposes. Always consult the official Hitachi service manual for your specific machine serial number and seek assistance from certified heavy equipment technicians when performing diagnostics or repairs. Improper troubleshooting can lead to equipment damage or safety hazards.