What is Hitachi ZX350H-5G Fault Code 20105-2?

Fault Code 20105-2 indicates a malfunction in the Engine Oil Pressure Sensor Circuit, specifically a low voltage or open circuit condition detected by the Engine Control Module (ECM). This code triggers when the sensor signal falls below the manufacturer's specified threshold, typically below 0.5 volts, suggesting either a faulty sensor, damaged wiring harness, or poor ground connection.

In the Hitachi ZX350H-5G excavator, the oil pressure sensor plays a critical role in monitoring engine lubrication system integrity. The ECM continuously monitors this sensor to prevent catastrophic engine damage from low oil pressure conditions. When this circuit fails, the engine protection system may activate, limiting machine performance or preventing startup altogether. For used excavators, this code frequently appears due to age-related connector corrosion or harness wear from engine vibration.

Common Symptoms

• Engine warning lamp illuminated on the instrument panel, often accompanied by an audible alarm
• Engine power derate or limited RPM, preventing the machine from reaching full operating capacity
• Engine shutdown or failure to start if the ECM enters protective mode
• Erratic oil pressure gauge readings or gauge stuck at zero despite adequate oil level
• Intermittent code appearance that correlates with engine vibration or temperature changes

Potential Causes

The most common causes for Code 20105-2 on used ZX350H-5G excavators include:

• Faulty oil pressure sensor with internal electrical failure (common after 5,000+ operating hours)
• Damaged wiring harness between the sensor and ECM, particularly at flex points near the engine mount where vibration causes wire fatigue
• Corroded or loose connector pins at the sensor connection point—a frequent issue in machines exposed to moisture or extreme conditions
• Poor ground connection at the sensor mounting point due to oil contamination or corrosion buildup
• ECM internal fault (rare, but possible in older machines with electrical system damage)
• Broken or chafed wires where the harness contacts the engine block or frame

How to Troubleshoot and Fix Code 20105-2

Step 1: Visual Inspection Begin by locating the oil pressure sensor on the engine block (typically near the oil filter housing). Inspect the wiring harness from sensor to ECM for obvious damage, including chafing, burns, or oil contamination. Check the connector for bent pins, corrosion (green/white deposits), or moisture intrusion—common issues in used excavators.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure resistance across the sensor terminals. Compare readings to manufacturer specifications (typically 50-250 ohms depending on temperature). Check for continuity in the wiring harness from the sensor connector to the ECM pins. Measure voltage supply from the ECM to the sensor—should read approximately 5 volts with ignition on.

Step 3: Sensor and Ground Verification Test the ground circuit by measuring resistance between the sensor ground terminal and a known good chassis ground (should be less than 1 ohm). For used machines, remove the sensor and inspect the mounting threads for oil sludge buildup that can compromise grounding. Clean mounting surfaces thoroughly before reinstalling.

Step 4: Component Replacement If testing confirms sensor failure, replace with a genuine Hitachi oil pressure sensor or OEM-equivalent part. When working on used excavators, always apply dielectric grease to connector pins to prevent future corrosion. If wiring damage is found, repair using proper gauge wire and heat-shrink connectors rather than temporary fixes.

Step 5: System Reset and Verification After repairs, clear the fault code using Hitachi Dr.EX diagnostic software or an appropriate scan tool. Start the engine and monitor oil pressure readings while observing for code recurrence. Perform a function test under load to ensure proper sensor operation across varying RPM ranges.

---

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 professional assistance from certified technicians when working with critical engine systems. Improper diagnosis or repair may result in equipment damage or safety hazards.