What is Hitachi ZX670LC-5A Fault Code 20105-2?

Fault Code 20105-2 indicates a malfunction in the Engine Air Temperature Sensor Circuit, specifically detecting an abnormally high voltage signal or open circuit condition. This code is triggered when the Engine Control Module (ECM) receives a voltage reading outside the acceptable range from the Intake Air Temperature (IAT) sensor, which monitors the temperature of air entering the engine's combustion system.

On the Hitachi ZX670LC-5A, this sensor is critical for proper fuel injection timing and air-fuel mixture calculations. The ECM uses intake air temperature data to adjust engine performance parameters, ensuring optimal combustion efficiency and emissions compliance. When this circuit fails, the engine defaults to a predetermined value, which can significantly impact fuel economy and performance, especially under varying ambient conditions or heavy load operations.

Common Symptoms

When fault code 20105-2 is active, operators typically experience:

• Check Engine Warning Light illuminated on the instrument cluster with possible reduced engine power mode
• Hard starting conditions, particularly in cold weather, due to improper fuel mixture calculations
• Black smoke from exhaust indicating rich fuel condition as the ECM compensates for missing temperature data
• Rough idle or engine hesitation during acceleration, especially when the machine is cold
• Decreased fuel efficiency as the engine management system cannot optimize combustion without accurate air temperature readings

Potential Causes

The most common technical reasons for this fault code on used ZX670LC-5A excavators include:

• Open circuit or broken wiring in the IAT sensor harness, particularly at flex points near the air intake manifold where vibration causes wire fatigue
• Corroded or loose connector pins at the sensor plug—a frequent issue in machines operating in dusty or humid environments
• Failed IAT sensor element due to age-related degradation or contamination from oil vapors in the intake system
• Damaged sensor mounting boss causing air leaks that affect sensor readings
• ECM internal circuit failure (rare, but possible in high-hour machines with electrical system stress)
• Aftermarket air filter housing modifications that damaged original wiring routing

How to Troubleshoot and Fix Code 20105-2

Step 1: Visual Inspection and Connector Check Locate the IAT sensor on the intake manifold (typically integrated into the air intake piping between the air filter and turbocharger). Disconnect the sensor connector and carefully inspect both the sensor pins and harness connector for corrosion, bent pins, moisture, or physical damage. On used excavators, pay special attention to wire insulation chafing where the harness contacts metal edges or vibrates against brackets.

Step 2: Sensor Resistance Testing Using a digital multimeter (DMM), measure the resistance across the IAT sensor terminals. At approximately 20°C (68°F), resistance should read between 2,000-3,000 ohms (consult your service manual for exact specifications). If the reading shows infinite resistance (open circuit) or zero ohms (short circuit), replace the sensor. For accurate diagnosis, compare readings at different temperatures—resistance should decrease as temperature increases.

Step 3: Circuit Voltage and Wiring Verification With the sensor disconnected and ignition ON (engine off), measure voltage at the harness connector. You should see approximately 5 volts reference voltage on the signal wire from the ECM. If voltage is absent, trace the wiring back to the ECM connector checking for breaks, especially at common failure points like cable ties and harness pass-throughs. Use Hitachi Dr.EX diagnostic software if available to monitor live sensor data and verify the ECM is receiving proper signals.

Step 4: Repair and Clear Code Replace faulty components—whether sensor, connector, or damaged wiring. For used machines, consider applying dielectric grease to connectors to prevent future corrosion. After repairs, clear the fault code using diagnostic software or by disconnecting the battery for 5 minutes, then run the engine through multiple temperature cycles to confirm the repair.

Disclaimer: This guide provides general diagnostic information. Always consult the official Hitachi service manual for your specific machine serial number and software version. Complex electrical issues may require professional diagnosis with factory-level diagnostic equipment.