What is Hitachi ZH200LC-5A Fault Code 172-4?

Fault Code 172-4 on the Hitachi ZH200LC-5A excavator indicates an abnormal voltage signal detected in the engine coolant temperature sensor circuit, specifically reporting a voltage level that is too high (open circuit or high resistance condition). This code is generated when the Engine Control Module (ECM) receives a signal outside the normal operating range from the coolant temperature sensor, typically above 4.5-4.8 volts when expecting a range between 0.5-4.5 volts during normal operation.

This fault is critical for the ZH200LC-5A's performance because the ECM relies on accurate coolant temperature data to manage fuel injection timing, engine protection protocols, and cold-start enrichment. When this sensor circuit fails, the ECM cannot properly protect the engine from overheating or optimize combustion efficiency, potentially leading to reduced performance or component damage.

Common Symptoms

• Check Engine light or warning lamp illuminated on the operator display panel
• Engine may enter derate mode or experience reduced power output as a protective measure
• Difficulty starting in cold conditions due to improper fuel enrichment calculations
• Cooling fan running continuously at maximum speed regardless of actual engine temperature
• Inaccurate or frozen temperature gauge readings on the instrument cluster

Potential Causes

The most common technical causes for Code 172-4 on used ZH200LC-5A excavators include:

• Damaged or disconnected coolant temperature sensor connector, often caused by vibration or harness movement near the engine block
• Open circuit in the sensor wiring harness, particularly at rub points where the harness contacts the engine or frame (common failure area behind the fuel filter assembly)
• Failed coolant temperature sensor itself, with internal element deterioration causing high resistance readings
• Corroded connector pins at the ECM or sensor connection points due to moisture ingress over years of operation
• Damaged ECM internal circuitry (rare, but possible in high-hour used machines)

How to Troubleshoot and Fix Code 172-4

Step 1: Visual Inspection Begin by inspecting the coolant temperature sensor located on the engine cylinder head near the thermostat housing. Check the connector for corrosion, bent pins, or moisture. On used excavators, examine the entire wiring harness for signs of chafing, especially where it routes near moving components or sharp edges.

Step 2: Electrical Testing Disconnect the sensor and use a digital multimeter to measure resistance across the sensor terminals. A functioning sensor should read approximately 2,000-3,000 ohms at room temperature (refer to Hitachi service manual for exact specifications). Check for continuity in the wiring from sensor to ECM—infinite resistance indicates an open circuit.

Step 3: Voltage Check With the ignition on and sensor disconnected, measure reference voltage at the harness connector. You should see approximately 5 volts supplied by the ECM. If voltage is absent, trace the power supply wire back toward the ECM for breaks or shorts.

Step 4: Component Replacement If testing confirms sensor failure, replace with a genuine Hitachi or OEM-equivalent part. For used excavators with high operating hours, consider replacing the connector pigtail simultaneously to prevent future corrosion-related failures. Clear the fault code using Hitachi diagnostic software (Dr.EX) or compatible scan tool and verify proper operation.

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Disclaimer: This guide provides general diagnostic information. Always consult the official Hitachi service manual for your specific machine serial number and consider professional diagnosis for complex electrical issues or if you're unfamiliar with high-voltage systems.