What is Hitachi ZX360LC-5G Fault Code 16605-2?

Fault Code 16605-2 indicates a malfunction in the DEF (Diesel Exhaust Fluid) pump control circuit, specifically a short to ground condition. This code is part of the SCR (Selective Catalytic Reduction) emissions system that is critical for meeting Tier 4 Final emission standards on the ZX360LC-5G excavator.

The DEF pump is responsible for delivering precise amounts of urea solution into the exhaust stream to reduce NOx emissions. When the ECM (Engine Control Module) detects abnormal electrical resistance or a ground fault in the pump's control wiring, it triggers code 16605-2. This fault compromises the machine's ability to properly treat exhaust gases, which can lead to derate conditions or complete shutdown if not addressed promptly. On used excavators, this system is particularly vulnerable due to exposure to harsh jobsite conditions and accumulated operating hours.

Common Symptoms

• DEF/Exhaust warning lamp illuminated on the instrument cluster (amber or red)
• Engine power derate after a grace period, typically reducing output by 25-40%
• DEF consumption drops to zero or becomes irregular despite normal operation
• Stored fault codes in the ECM memory, visible through diagnostic software
• Possible engine shutdown warning displayed on the monitor after extended operation with active fault

Potential Causes

The most common technical causes for code 16605-2 on used ZX360LC-5G excavators include:

• Damaged DEF pump wiring harness, particularly near the engine mount points where vibration causes wire insulation to wear through and contact the frame
• Corroded or moisture-contaminated connectors at the DEF pump electrical connection, common in machines operated in wet or coastal environments
• Failed DEF pump motor or internal short within the pump assembly itself, typically after 6,000-8,000 operating hours
• Chafed wiring along the chassis rail where the harness routes near sharp edges or mounting brackets
• ECM internal fault (rare) where the control module's output driver circuit has failed

How to Troubleshoot and Fix Code 16605-2

Step 1: Visual Inspection Begin by thoroughly inspecting the DEF pump wiring harness from the ECM to the pump assembly. On used excavators, check for obvious damage, particularly at known rub points near the fuel tank mounting area and along the right-hand chassis rail. Disconnect the DEF pump connector and inspect pins for corrosion, bent terminals, or moisture intrusion.

Step 2: Electrical Testing Using a digital multimeter, perform resistance checks on the DEF pump control circuit. With the harness disconnected at both ends, measure resistance from the pump side connector to chassis ground—it should read OL (open/infinite). If you measure less than 10,000 ohms, you have confirmed a short to ground. Next, check the pump motor resistance across the pump connector terminals (typically 3-8 ohms depending on temperature).

Step 3: Isolate the Fault Disconnect the harness at the ECM and measure resistance between the control wire pins and ground. This isolates whether the short exists in the harness or the pump itself. For used machines, pay special attention to harness sections that pass through grommets or near moving components—these are high-wear areas.

Step 4: Repair or Replace If wiring damage is found, repair using OEM-spec wire and proper heat-shrink connectors rated for diesel fuel and DEF exposure. If the DEF pump itself shows internal short circuit, replacement is required (Hitachi part number varies by production date). After repairs, clear codes using Dr.EX diagnostic software or equivalent Hitachi diagnostic tool, and perform a system function test to verify proper DEF dosing.

Professional Disclaimer: This guide provides general troubleshooting information. Always consult the official Hitachi service manual for your specific serial number range and consider professional diagnostic assistance for complex electrical issues or if you're unfamiliar with high-pressure DEF systems.