What is Hitachi ZX870LC-5A Fault Code 14104-2?

Fault Code 14104-2 indicates a malfunction in the Engine Speed Sensor Circuit - Abnormal Signal Detected. This diagnostic trouble code (DTC) is triggered when the Electronic Control Module (ECM) receives an irregular or intermittent signal from the engine speed sensor (also called crankshaft position sensor), which monitors the rotational speed and position of the engine's crankshaft.

This fault is critical for the ZX870LC-5A because the engine speed sensor provides essential data that the ECM uses to control fuel injection timing, engine speed regulation, and overall performance. When signal integrity is compromised, the excavator may experience reduced power output, erratic engine behavior, or complete shutdown to protect the engine from potential damage.

Common Symptoms

Operators and mechanics typically observe the following when Code 14104-2 is active:

• Check Engine Light or malfunction indicator illuminated on the instrument panel
• Engine derate mode activated, limiting maximum RPM and hydraulic performance
• Rough idle or inconsistent engine speed fluctuations, especially during startup
• Intermittent stalling or unexpected engine shutdown during operation
• Reduced hydraulic response due to power limitations imposed by the ECM

Potential Causes

The most common technical reasons for this fault code on used ZX870LC-5A excavators include:

• Damaged or corroded engine speed sensor connector – moisture intrusion and corrosion are prevalent in older machines
• Worn or failing engine speed sensor – internal component degradation after extended operating hours
• Damaged sensor wiring harness – particularly at known rub points near the engine block or frame where vibration causes insulation wear
• Loose or damaged sensor mounting – allowing excessive air gap between sensor and reluctor wheel
• ECM internal fault – less common but possible in high-hour machines with electrical system history
• Intermittent ground connection – corroded ground points affecting signal quality

How to Troubleshoot and Fix Code 14104-2

Step 1: Visual Inspection Begin by inspecting the engine speed sensor located on the engine block near the flywheel housing. Check for physical damage, oil contamination, or improper mounting. Verify the air gap between sensor tip and reluctor wheel is within specification (typically 0.5-1.5mm). On used excavators, carefully examine the wiring harness for signs of chafing, especially where it routes near hot or moving components.

Step 2: Electrical Testing Using a digital multimeter, check sensor resistance (typically 190-250 ohms, but verify with Hitachi specifications). Inspect the connector pins for corrosion, bent terminals, or moisture. Test voltage output while cranking the engine – you should see an AC voltage signal that increases with engine speed. Check continuity from sensor connector back to the ECM to identify any open circuits.

Step 3: Signal Analysis and Component Replacement Connect Hitachi Dr.EX diagnostic software or compatible scan tool to monitor live sensor data. Observe for signal dropouts or erratic readings during engine operation. If electrical tests pass but the signal remains abnormal, replace the engine speed sensor with a genuine Hitachi part. For used machines with over 8,000 hours, consider replacing the sensor harness simultaneously, as internal wire degradation may not be visible externally.

Step 4: Post-Repair Verification After repairs, clear the fault code using diagnostic software and perform a complete operational test under load. Monitor for code recurrence during a full work cycle.

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Disclaimer: This guide provides general troubleshooting information. Always consult the official Hitachi service manual for your specific machine serial number and seek assistance from certified Hitachi technicians for complex electrical diagnostics or if you're unfamiliar with high-voltage systems.