What is Hitachi ZX350H-5G Fault Code 14105-2?

Fault Code 14105-2 indicates an abnormal voltage condition in the Engine Control Module (ECM) power supply circuit, specifically a low voltage or intermittent power feed to the main engine control system. This diagnostic trouble code (DTC) is triggered when the ECM detects that incoming voltage from the machine's electrical system has dropped below the manufacturer's specified threshold or is experiencing irregular fluctuations during operation.

In the Hitachi ZX350H-5G excavator, this code directly affects the Isuzu engine control system, which relies on stable voltage (typically 24V nominal) to maintain precise fuel injection timing, sensor readings, and emission controls. When voltage irregularities occur, the ECM cannot properly regulate engine performance, potentially leading to derated power output or unexpected shutdowns. For used excavators operating in demanding environments, this fault often stems from aging electrical infrastructure rather than catastrophic component failure.

Common Symptoms

• Engine warning lamp illuminated on the instrument cluster, often accompanied by reduced engine power (derate mode)
• Intermittent engine stalling or difficulty starting, particularly after the machine has warmed up
• Erratic engine RPM fluctuations at idle or under load, even with consistent throttle input
• Diagnostic display showing multiple simultaneous codes related to various sensors (false codes triggered by voltage instability)
• Electrical accessories (lights, monitors) dimming or flickering during engine operation

Potential Causes

The most common technical causes for Code 14105-2 on used ZX350H-5G excavators include:

• Main battery cables with corroded terminals or loose connections at the battery posts or starter relay, reducing available voltage to the ECM
• Failing alternator unable to maintain proper charging voltage (should output 27-29V on this 24V system), especially common in machines exceeding 6,000 operating hours
• Damaged or chafed engine harness wiring between the main power relay and ECM connector—known wear points include routing near the turbocharger and along the engine block
• Faulty ECM power relay with burned contacts or weak coil, creating intermittent power delivery
• Corroded pins in the ECM connector (C101), particularly in machines exposed to moisture or operating in coastal/high-humidity environments
• Degraded chassis ground points where engine harness grounds connect to the frame, creating voltage drop under load

How to Troubleshoot and Fix Code 14105-2

Step 1: Verify Battery and Charging System Baseline Using a digital multimeter, measure battery voltage with the engine off (should read 24-26V) and running (27-29V). Check both batteries individually—on used excavators, mismatched or weak batteries create voltage imbalance. Load test batteries and inspect all battery cable connections for white/green corrosion. Clean terminals with a wire brush and apply dielectric grease.

Step 2: Inspect ECM Power Supply Circuit Locate the main ECM power relay in the electrical box (typically mounted behind the operator cab). With ignition on/engine off, verify the relay clicks when activated. Measure voltage at the relay output terminal—should match battery voltage. Trace the power supply harness from relay to the ECM connector, checking for damaged insulation, particularly where the harness passes near hot engine components or sharp edges.

Step 3: Test ECM Connector and Grounds Disconnect the ECM main connector (C101) and inspect all pins for corrosion, bent contacts, or moisture intrusion—common in used machines. Using a multimeter, check continuity from ECM ground pins to known good chassis ground (should read less than 0.5 ohms resistance). Measure incoming voltage at the power pins with ignition on (should be stable battery voltage). For used excavators, pay special attention to harness rub points where vibration causes intermittent opens.

Step 4: Monitor Voltage Under Load Reconnect all components and use Hitachi Dr.EX diagnostic software or an aftermarket scan tool to monitor live ECM voltage while operating the machine through work cycles. Voltage should remain above 22V even under maximum hydraulic load. Drops below this threshold indicate charging system inadequacy or excessive resistance in power delivery circuits.

Disclaimer: This guide provides general troubleshooting information for experienced technicians. Always consult the official Hitachi service manual for your specific machine serial number and software version. If electrical diagnostics are beyond your expertise, consult a certified Hitachi technician to prevent ECM damage or safety hazards.