What is Hitachi ZX210H-5G-HCMC Fault Code 16605-2?

Fault Code 16605-2 indicates a malfunction in the Engine Control Module (ECM) communication circuit, specifically pointing to an intermittent or complete loss of CAN (Controller Area Network) data transmission between the engine ECM and the hydraulic control system. This diagnostic trouble code (DTC) is part of Hitachi's proprietary onboard diagnostics for their fifth-generation hydraulic excavators equipped with Isuzu industrial diesel engines.

The CAN bus network serves as the central nervous system for modern excavators, allowing critical subsystems to exchange real-time operational data. When code 16605-2 triggers, the ECM cannot properly communicate with hydraulic controllers, potentially causing the machine to enter a protective derate mode or limiting certain functions. For the ZX210H-5G-HCMC model specifically, this communication failure can compromise fuel efficiency calibrations and coordinated control between engine output and hydraulic demand—critical for optimal performance in used machines where component wear already affects system tolerances.

Common Symptoms

• Amber warning lamp illuminated on the instrument cluster with possible "Check Engine" or communication error messages on the monitor display
• Intermittent loss of hydraulic power or sluggish response during combined operations (swing + boom movements)
• Engine derate limiting RPM to approximately 1,500-1,800 range, preventing full throttle operation
• Erratic gauge readings including fuel level, coolant temperature, or hydraulic oil temperature displaying incorrect or fluctuating values
• Inability to access diagnostics through the machine's built-in monitor or external diagnostic tools showing connection failures

Potential Causes

The most common technical failures triggering code 16605-2 on used Hitachi excavators include:

• Corroded or damaged CAN bus connectors at the ECM harness (C101 connector behind the operator cab is a known vulnerable point)
• Chafed wiring harness where the engine harness passes through the chassis frame near the right-hand swing bearing—vibration and rubbing create intermittent shorts
• Failed termination resistor in the CAN network (120-ohm resistors at network endpoints deteriorate over time)
• ECM internal communication module failure due to voltage spikes or moisture intrusion in older units
• Loose or oxidized ground connections at G201 ground point on the engine block
• Aftermarket radio or accessory installations that improperly tap into the electrical system, creating voltage interference

How to Troubleshoot and Fix Code 16605-2

Step 1: Visual Inspection and Connector Verification Begin by inspecting all CAN bus connectors along the engine-to-chassis harness. Disconnect the main ECM connector (C101) located behind the cab's right side panel. Examine pins for corrosion, bent terminals, or moisture. On used excavators, this connector frequently shows green oxidation due to seal degradation. Clean contacts with electrical contact cleaner and apply dielectric grease before reconnection.

Step 2: CAN Bus Continuity and Resistance Testing Using a digital multimeter, measure resistance between CAN-High and CAN-Low terminals at the ECM connector with all modules disconnected. You should read approximately 60 ohms (two 120-ohm terminating resistors in parallel). A reading of 120 ohms indicates one termination resistor has failed; open circuit (OL) means wiring break or both resistors failed. Check for short to ground on both CAN lines—any reading below 10k ohms indicates harness damage.

Step 3: Harness Routing and Chafe Point Inspection Physically trace the engine harness from the ECM to the chassis connector, paying particular attention to the routing near the swing bearing and battery box area. On ZX210H-5G models with over 5,000 hours, the harness protective loom often wears through at the frame pass-through point. Look for exposed copper wire or damaged insulation. Repair any damage with proper gauge wire and re-route with additional protective sleeving.

Step 4: Diagnostic Software Verification Connect Hitachi Dr.EX diagnostic software or compatible J1939 diagnostic tool to verify active and pending codes. Monitor live CAN bus traffic while operating the machine. Intermittent dropouts visible in the data stream confirm wiring issues rather than ECM failure. Clear codes after repairs and perform a stationary regeneration test to verify stable communication under load.

Step 5: Ground Circuit and Power Supply Check Verify battery voltage remains stable at 24-28V DC during starting and operation. Check all chassis ground points, especially G201 on the engine block and G105 near the hydraulic pump. Clean ground surfaces to bare metal and apply anti-corrosion compound. Poor grounds are responsible for approximately 40% of communication codes in used equipment.

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Disclaimer: This guide provides general troubleshooting information for experienced technicians. Always consult the official Hitachi service manual for your specific serial number range and follow proper lockout/tagout procedures. If unfamiliar with high-voltage electrical diagnostics or CAN bus systems, consult a certified Hitachi dealer or qualified heavy equipment electrician to prevent further damage to electronic modules.