What is Hitachi ZX350H-5G Fault Code 11602-2?

Fault Code 11602-2 indicates a malfunction in the engine coolant temperature sensor circuit, specifically a signal voltage that is too low or intermittent. This code is triggered when the Engine Control Module (ECM) detects that the coolant temperature sensor is sending a voltage reading below the acceptable threshold, typically below 0.2-0.3 volts, or the signal is cutting in and out.

This fault affects the Isuzu engine used in the ZX350H-5G excavator's ability to properly manage fuel injection timing, idle speed, and emissions control. The coolant temperature sensor is critical because it informs the ECM whether the engine is cold or at operating temperature, directly impacting performance and fuel efficiency. In used machines, this sensor and its wiring harness are particularly vulnerable to corrosion and physical damage from engine vibration.

Common Symptoms

When Code 11602-2 is active, operators may experience:

• Check Engine Light or warning indicator illuminated on the dashboard display
• Hard starting or extended cranking time, especially during cold starts
• Rough idle or irregular engine RPM when the machine is first started
• Excessive black smoke from the exhaust due to improper fuel mixture
• Reduced engine performance or power derate mode activation in severe cases

Potential Causes

The most common technical causes for this fault code on used ZX350H-5G excavators include:

• Damaged or corroded coolant temperature sensor connector – extremely common on machines with 5,000+ hours due to heat cycling and moisture intrusion
• Broken or shorted sensor wiring – particularly at harness rub points near the engine block or valve cover
• Failed coolant temperature sensor – internal sensor element deterioration from prolonged thermal stress
• Poor ground connection at the sensor or ECM ground points
• ECM internal circuit failure – rare but possible on high-hour machines with electrical history

How to Troubleshoot and Fix Code 11602-2

Step 1: Visual Inspection Locate the coolant temperature sensor on the engine block (typically near the thermostat housing). Inspect the sensor connector and wiring harness for corrosion, oil contamination, pin damage, or visible wire chafing. On used excavators, check for harness routing issues where wires contact hot engine components.

Step 2: Electrical Testing Disconnect the sensor and use a digital multimeter to check sensor resistance. At room temperature (68°F/20°C), resistance should read approximately 2,000-3,000 ohms. Test the harness voltage at the connector with ignition on – you should see approximately 5 volts reference voltage from the ECM.

Step 3: Signal Wire and Ground Testing Check continuity between the sensor signal wire and the ECM connector. Resistance should be less than 5 ohms. Verify the sensor ground circuit has less than 0.5 ohms resistance to chassis ground. Wiggle the harness while monitoring voltage to identify intermittent connections.

Step 4: Component Replacement If the sensor tests faulty, replace it with a genuine Hitachi or OEM-equivalent part. Clean the connector with electrical contact cleaner and apply dielectric grease to prevent future corrosion. If wiring is damaged, repair or replace the affected harness section with proper heat-shrink connections.

Disclaimer: This guide provides general troubleshooting information. Always consult the official Hitachi service manual and consider professional diagnostic assistance for complex electrical issues or if you lack proper diagnostic equipment.