What is Hitachi ZX350LCK-5G Fault Code 16607-2?

Fault Code 16607-2 on the Hitachi ZX350LCK-5G excavator indicates a malfunction in the DEF (Diesel Exhaust Fluid) pump motor circuit, specifically a current-related abnormality or short circuit condition. This code is part of Hitachi's emissions control diagnostics within the SCR (Selective Catalytic Reduction) system, monitored by the machine's ECM (Engine Control Module).

The DEF pump is critical for injecting precise amounts of diesel exhaust fluid into the exhaust stream to reduce NOx emissions and meet Tier 4 Final standards. When code 16607-2 triggers, the ECM detects abnormal current flow—either excessive amperage suggesting a short circuit, or insufficient current indicating an open circuit or pump motor failure. Left unaddressed, this fault can cause the machine to enter derate mode, significantly reducing engine power and affecting productivity on jobsites.

Common Symptoms

• DEF system warning light illuminated on the instrument panel, often accompanied by a check engine light
• Engine power derate after a grace period (typically 50-100 operating hours), limiting maximum RPM and hydraulic performance
• DEF fluid not being consumed at normal rates, indicating the pump isn't operating
• Audible alarm or continuous beeping when starting the machine or during operation
• Error messages displayed on the monitor screen specifically referencing DEF system malfunction

Potential Causes

The most common technical causes for code 16607-2 on used ZX350LCK-5G excavators include:

• DEF pump motor failure due to crystallized urea buildup from contaminated or old DEF fluid causing internal seizure
• Wiring harness damage at known rub points near the DEF tank mounting bracket where vibration causes wire insulation wear
• Corroded or moisture-damaged connectors on the DEF pump electrical connection, especially on machines operating in wet or coastal environments
• Short circuit to ground in the pump motor wiring, often found where harnesses route along the chassis frame
• ECM internal driver circuit failure, less common but possible in high-hour machines with electrical system stress
• Faulty DEF pump relay or fuse in the power distribution circuit supplying the pump motor

How to Troubleshoot and Fix Code 16607-2

Step 1: Visual Inspection and Connector Check Begin by disconnecting the battery and locating the DEF pump assembly mounted on or near the DEF tank. Inspect the electrical connector for corrosion, bent pins, or moisture intrusion—common issues on used excavators. Check the wiring harness routing for any visible damage, particularly where it contacts frame components or passes through grommets.

Step 2: Electrical Testing with Multimeter Using a quality digital multimeter, measure the resistance across the DEF pump motor terminals (with connector disconnected). Typical resistance should be 2-6 ohms; readings near zero indicate a short circuit, while infinite resistance suggests an open circuit or failed motor. Next, check for short to ground by measuring resistance between each pump terminal and chassis ground—readings should be infinite (open circuit).

Step 3: Power Supply Verification Reconnect the pump connector and check for proper voltage supply at the harness side with ignition on (typically 12V). If voltage is absent, trace back through the fuse panel and relay to identify power supply issues. For used excavators, pay special attention to corroded fuse holders or relay sockets.

Step 4: DEF Quality and Pump Mechanical Inspection Drain a sample of DEF fluid and inspect for contamination or crystallization. Old or contaminated DEF causes pump motor seizure. If electrical tests pass but the code persists, the pump motor may be mechanically seized—remove the pump and attempt manual rotation of the motor shaft.

Step 5: Advanced Diagnostics Connect Hitachi Dr.EX diagnostic software to verify ECM operation and view real-time pump motor current draw. Normal operating current is typically 3-8 amps; significantly higher readings confirm internal motor short circuits.

For used machinery, always inspect harness routing and add protective sleeving at wear points before replacing components. Many 16607-2 codes result from preventable wiring damage rather than pump failure.

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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 consider professional diagnostic services for complex electrical issues or warranty concerns.