What is Hitachi ZW310-5A Fault Code 111702-10?

Fault Code 111702-10 on the Hitachi ZW310-5A wheel loader indicates a short circuit to ground in the Engine Coolant Temperature (ECT) sensor circuit. This diagnostic trouble code (DTC) is triggered when the Electronic Control Module (ECM) detects an abnormally low voltage reading on the coolant temperature sensor signal wire, typically below 0.2 volts, indicating the circuit has made unintended contact with chassis ground.

This code is critical for the ZW310-5A because the ECT sensor provides essential temperature data to the ECM for proper fuel injection timing, engine protection systems, and cooling fan operation. When this circuit fails, the engine management system cannot accurately monitor operating temperatures, potentially leading to overheating conditions or unnecessary engine derating to protect components.

Common Symptoms

• Check Engine Light or warning lamp illuminated on the instrument cluster
• Engine may enter derate mode (reduced power output) as a protective measure
• Cooling fan runs continuously at high speed regardless of actual engine temperature
• Erratic temperature gauge readings or gauge stuck at cold position
• Difficulty starting in cold conditions due to improper cold-start fuel enrichment
• Possible white smoke on startup from incorrect fuel mapping

Potential Causes

The most common technical causes for Code 111702-10 on used ZW310-5A machines include:

• Damaged sensor wiring harness where cables rub against the engine block near the thermostat housing—a known wear point on this model
• Corroded or moisture-infiltrated connector pins at the ECT sensor plug, especially on machines operated in wet or coastal environments
• Failed ECT sensor with internal short circuit (less common but possible after 5,000+ operating hours)
• Chafed insulation on signal wire due to improper routing during previous repairs
• Contaminated ECM connector terminals causing intermittent ground faults
• Aftermarket sensor installations with incompatible resistance values

How to Troubleshoot and Fix Code 111702-10

Step 1: Visual Inspection Begin by locating the ECT sensor on the engine block near the thermostat housing. Inspect the entire wiring harness from sensor to ECM for visible damage, abrasion points, or melted insulation. On used excavators, pay special attention to areas where harnesses contact moving parts or sharp edges—this is the most common failure point.

Step 2: Connector and Pin Check Disconnect the ECT sensor connector and thoroughly inspect both male and female terminals for corrosion, bent pins, or moisture. Clean contacts with electrical contact cleaner and verify proper pin tension. Check the connector seal for damage that would allow water intrusion.

Step 3: Electrical Testing Using a digital multimeter (DMM), measure resistance across the ECT sensor terminals with the sensor disconnected. At 68°F (20°C), resistance should typically read 2,000-3,000 ohms (consult service manual for exact specs). Next, test for continuity between the signal wire and chassis ground with the harness disconnected from the ECM—any continuity indicates a short to ground.

Step 4: Circuit Isolation Disconnect the harness at both the sensor and ECM. Measure resistance of the signal wire end-to-end; it should read near zero ohms. Then check signal wire to ground wire within the same harness—infinite resistance confirms wire integrity. If short persists, methodically inspect the harness routing for pinch points.

Step 5: Component Replacement If wiring tests acceptable, replace the ECT sensor with OEM Hitachi parts (avoid cheap aftermarket sensors). After replacement, clear codes using Hitachi Dr.EX diagnostic software or compatible scan tool and verify repair with a test cycle.

Disclaimer: This guide provides general troubleshooting information. Always consult the official Hitachi service manual for your specific machine serial number. If unfamiliar with electrical diagnostics or working around high-temperature engine components, seek assistance from a certified Hitachi technician or qualified heavy equipment mechanic.