What is Hitachi ZX350LCK-5G Fault Code 14106-2?

Fault Code 14106-2 indicates a DEF (Diesel Exhaust Fluid) Pressure Sensor Circuit Low Voltage condition in the Selective Catalytic Reduction (SCR) system of the Hitachi ZX350LCK-5G excavator. This diagnostic trouble code triggers when the Engine Control Module (ECM) detects voltage readings from the DEF pressure sensor falling below the manufacturer's specified threshold, typically under 0.5 volts for this system.

The SCR system is critical for meeting Tier 4 Final emissions standards on this model. The DEF pressure sensor monitors fluid pressure in the dosing supply line to ensure proper urea injection into the exhaust stream. When this sensor reports abnormally low voltage, the ECM cannot accurately control DEF delivery, potentially causing emissions non-compliance and triggering derate protocols that limit machine performance.

Common Symptoms

• Amber warning light illuminated on the instrument cluster with SCR system fault message
• Engine power derate after a countdown timer expires (typically 4-8 hours of continued operation)
• Reduced hydraulic performance once derate activates, limiting digging force and travel speed
• DEF consumption irregularities or complete cessation of DEF usage indicated by tank level remaining static
• Multiple related fault codes may appear simultaneously, including DEF quality or heater circuit codes

Potential Causes

On used excavators like the ZX350LCK-5G, this code typically stems from age-related deterioration rather than component manufacturing defects. The DEF pressure sensor wiring harness commonly experiences abrasion where it routes near the chassis frame rail behind the fuel tank—a known friction point on this model series. Connector corrosion at the sensor plug is prevalent in machines operating in wet or high-humidity environments, as moisture infiltration degrades pin contacts.

The sensor itself may fail internally due to crystallized DEF contamination if the system wasn't properly purged during extended storage. Voltage supply issues from the ECM can occur due to corroded grounds at the chassis mounting point near the right-side battery box. In higher-hour machines, harness chafing against the DEF tank mounting bracket frequently causes intermittent short-to-ground conditions.

How to Troubleshoot and Fix Code 14106-2

Step 1: Initial Inspection and Voltage Verification Begin with a visual inspection of the DEF pressure sensor located on the DEF supply module near the dosing pump. Disconnect the sensor connector and inspect for white crystalline DEF deposits, green corrosion, or bent pins. Using a digital multimeter, check for proper 5-volt reference supply from the ECM at the connector harness side (typically pin 1). Verify less than 0.5 ohms resistance on the ground circuit (typically pin 3) back to chassis ground.

Step 2: Sensor Circuit Testing With the sensor connected and ignition on (engine off), backprobe the signal wire (typically pin 2) and measure voltage. A properly functioning sensor should read 0.5-4.5 volts depending on DEF pressure. If voltage reads near zero with the system unpressurized, suspect a short-to-ground in the harness. Perform a resistance check between the signal wire and ground with the sensor disconnected—any reading below 10,000 ohms indicates harness damage. For used excavators, carefully trace the wiring harness along its entire route, paying special attention to zip-tie mounting points and areas where the harness contacts metal edges.

Step 3: Component Testing and Replacement If wiring checks pass, test the DEF pressure sensor directly by measuring its resistance across the signal and ground pins—specifications typically range from 250-500 ohms at room temperature (consult service manual for exact values). On used machines, remove the sensor and inspect the mounting boss for DEF crystallization that could create false readings. Clean the mounting area with distilled water and verify the O-ring seal isn't damaged. If sensor tests fail, replace with a genuine Hitachi part (part number typically starts with 4701916 for this model series). After replacement, use Hitachi diagnostic software (Dr.EX) to clear codes and perform a DEF system pressure test to verify proper operation.

Critical for Used Equipment: Before replacing the sensor, check the DEF tank vent filter and dosing unit for crystallization, as blockages can create abnormal pressure readings that mimic sensor failure. Inspect all harness connectors for corrosion using electrical contact cleaner, as this simple maintenance often resolves the issue without parts replacement.

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Disclaimer: This guide provides general diagnostic information based on common failure patterns. Always consult the official Hitachi service manual for your specific machine serial number and torque specifications. If you're uncomfortable performing electrical diagnostics or lack proper diagnostic equipment, consult a certified Hitachi technician to prevent further damage to emissions control systems.