What is Hitachi ZX350LCK-5G Fault Code 11402-3?

Fault Code 11402-3 indicates a malfunction in the engine coolant temperature sensor circuit, specifically detecting an intermittent or erratic signal from the coolant temperature sensor to the Engine Control Module (ECM). This code is triggered when the ECM receives voltage readings outside the expected range or detects inconsistent data patterns from the temperature sensor circuit.

On the Hitachi ZX350LCK-5G excavator, this code directly affects the Isuzu engine's ability to properly manage fuel injection timing, idle speed, and engine protection protocols. The ECM relies on accurate coolant temperature data to optimize combustion efficiency and prevent overheating damage. When this sensor circuit fails, the engine may operate in a default "limp mode" with reduced performance to protect critical components.

Common Symptoms

• Check Engine Light or warning lamp illuminated on the instrument panel with possible coolant temperature gauge reading erratically or showing incorrect values
• Hard starting when the engine is cold, or excessive black smoke during warm-up due to improper fuel mixture calculations
• Engine derating or reduced power output as the ECM enters protective mode
• Cooling fan running continuously at high speed regardless of actual engine temperature
• Rough idle or hunting RPM, particularly noticeable during cold start conditions

Potential Causes

The most common technical causes for Code 11402-3 on used ZX350LCK-5G excavators include:

• Corroded or damaged wiring harness connections at the coolant temperature sensor plug, especially common where the harness runs near the engine block and experiences heat cycling
• Worn or failed coolant temperature sensor (CTS) due to age-related degradation or coolant contamination
• Chafed wiring at known rub points near the engine mount brackets or along the valve cover where harness protection may have deteriorated
• Intermittent ground connection in the sensor circuit causing voltage fluctuations
• Contaminated coolant causing sensor element corrosion or buildup affecting response time
• ECM connector pin corrosion at terminals specifically handling the CTS signal wire

How to Troubleshoot and Fix Code 11402-3

Step 1: Visual Inspection Begin by thoroughly inspecting the coolant temperature sensor and its wiring harness. Located on the engine block near the thermostat housing, check for physical damage, corrosion, or coolant leaks. On used excavators, pay special attention to harness wear points where vibration causes wire insulation breakdown.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure resistance across the sensor terminals. At 68°F (20°C), resistance should typically read 2,000-3,000 ohms (consult Hitachi service manual for exact specifications). Test the wiring harness for continuity between the sensor connector and ECM pins, checking for resistance below 5 ohms. Inspect for short circuits to ground.

Step 3: Signal Voltage Check With the sensor connected and ignition on (engine off), backprobe the sensor connector and verify reference voltage from the ECM (typically 5 volts). Monitor voltage while wiggling the harness to identify intermittent connections—voltage should remain stable.

Step 4: Connector Service Clean all connector terminals with electrical contact cleaner and apply dielectric grease. This is critical on used machines where moisture intrusion causes intermittent faults. Replace any corroded pins or damaged connector bodies.

Step 5: Component Replacement If testing confirms sensor failure, replace with a genuine Hitachi or OEM-equivalent coolant temperature sensor. After replacement, clear codes using Hitachi diagnostic software (Dr.EX) or a compatible scan tool and perform a test cycle.

Disclaimer: This guide provides general troubleshooting information. Always consult the official Hitachi service manual for your specific machine serial number and consider professional diagnostic assistance for complex electrical issues.