What is Hitachi ZX350LCK-5G Fault Code 11604-2?

Fault Code 11604-2 indicates a malfunction in the Diesel Particulate Filter (DPF) differential pressure sensor circuit, specifically a voltage signal that is too low or intermittent. This code is triggered when the Engine Control Module (ECM) detects that the differential pressure sensor, which monitors exhaust backpressure across the DPF, is sending a signal below the manufacturer's specified threshold (typically below 0.5V).

This sensor is critical for the ZX350LCK-5G's emissions control system and regeneration cycles. The ECM relies on accurate pressure readings to determine when the DPF requires active or passive regeneration. When this circuit fails, the machine cannot properly manage soot accumulation, potentially leading to engine derate, increased fuel consumption, and failed emissions compliance. For used excavators, this code often signals deteriorated wiring or sensor degradation from years of exposure to exhaust heat and vibration.

Common Symptoms

• Check Engine Light or DPF warning lamp illuminated on the instrument cluster
• Engine power derate or limited throttle response, particularly under heavy load conditions
• Inability to initiate or complete DPF regeneration cycles, resulting in continued warning messages
• Excessive black smoke from the exhaust during operation
• Abnormal fuel consumption patterns or rough idle conditions

Potential Causes

The most common causes for Code 11604-2 on used ZX350LCK-5G excavators include:

• Damaged or corroded wiring harness at the differential pressure sensor connector, especially where the harness routes near the turbocharger or exhaust manifold (known rub point on this model)
• Failed DPF differential pressure sensor due to carbon buildup on sensor ports or internal sensor element failure
• Corroded or loose electrical connectors at the sensor or ECM connection points
• Broken or kinked pressure sensing tubes running from the DPF to the sensor
• ECM internal fault (rare, but possible in high-hour machines)
• Poor ground connection at the sensor ground circuit due to rust or paint contamination

How to Troubleshoot and Fix Code 11604-2

Step 1: Visual Inspection Begin by locating the differential pressure sensor mounted on the exhaust system near the DPF. Inspect the wiring harness for obvious damage, melting, or chafing, particularly where it passes near hot exhaust components. On used excavators, check for hardened or cracked insulation from heat cycling. Examine both pressure sensing tubes for cracks, blockages, or disconnections.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and check the supply voltage at the harness connector with the ignition on—you should see approximately 5V reference voltage. Test sensor ground for continuity to chassis ground (should be less than 1 ohm). Check sensor resistance according to Hitachi specifications (typically 500-2000 ohms depending on temperature).

Step 3: Sensor and Tube Verification Remove the pressure sensing tubes and inspect for carbon blockage—blow compressed air through them carefully. If electrical tests pass but the code persists, replace the differential pressure sensor with a genuine Hitachi part. On used machines with over 6,000 hours, consider replacing the entire sensor harness as preventive maintenance, as insulation breakdown is common.

Step 4: Clear Code and Test After repairs, use Hitachi Dr.EX diagnostic software or equivalent to clear the fault code. Perform a DPF regeneration cycle and monitor live sensor data to confirm the pressure readings fluctuate normally (typically 0.5-4.5V during operation).

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Disclaimer: This guide provides general troubleshooting information. Always consult the official Hitachi service manual for your specific machine serial number and seek assistance from certified Hitachi technicians for complex repairs. Improper diagnosis can lead to costly component damage or safety hazards.