What is Hitachi EX200-3 Fault Code 656-3?

Fault Code 656-3 on the Hitachi EX200-3 excavator indicates a malfunction in the Engine Control Module (ECM) communication circuit, specifically related to the CAN (Controller Area Network) bus system experiencing intermittent or complete signal loss. This diagnostic trouble code signals that the ECM is unable to maintain consistent communication with other critical control modules, including the hydraulic control unit and instrument cluster.

This code is particularly critical for the EX200-3 because the ECM relies on continuous data exchange to regulate engine performance, hydraulic pressure modulation, and operator interface functions. When communication breaks down, the machine's integrated control systems cannot synchronize properly, leading to degraded performance or complete operational shutdown. For used excavators, this fault often stems from age-related deterioration of wiring harnesses and connector terminals that have endured years of vibration and environmental exposure.

Common Symptoms

• Intermittent or complete engine shutdown without warning, particularly during high-load operations
• Erratic instrument panel behavior, including flickering warning lights or inaccurate gauge readings
• Loss of hydraulic response precision, with delayed or inconsistent boom/bucket movements
• Engine derate mode activation, limiting RPM to approximately 1200-1500 to protect the powertrain
• Multiple fault codes appearing simultaneously due to cascading communication failures across modules

Potential Causes

The most common technical causes for Code 656-3 on used EX200-3 excavators include:

• Corroded or damaged CAN bus harness connectors, especially at the ECM plug (C101) and junction box connections behind the operator cab
• Frayed wiring in the main harness where it routes along the right-hand frame rail near the hydraulic pump—a known wear point on this model
• Failed terminating resistors (120-ohm) at either end of the CAN bus network
• ECM internal circuit board degradation from moisture intrusion through compromised seals
• Poor ground connections at G201 (frame ground near battery box) causing voltage reference issues
• Aftermarket component installation that improperly taps into the CAN network without proper isolation

How to Troubleshoot and Fix Code 656-3

Step 1: Visual Inspection and Connector Assessment Begin by inspecting all CAN bus harness connectors for corrosion, bent pins, or moisture. Focus on connector C101 at the ECM and C205 at the instrument cluster junction. Clean contacts with electrical contact cleaner and apply dielectric grease. On used excavators, check the harness routing along the right frame rail where it passes near the hydraulic tank—this is a common rub-through point on the EX200-3.

Step 2: Electrical Continuity and Resistance Testing Using a digital multimeter, disconnect the battery and measure resistance between CAN-High and CAN-Low terminals at the ECM connector. You should read approximately 60 ohms with both terminating resistors intact. Check each terminating resistor individually (should measure 120 ohms each). Verify continuity along the entire harness length, checking for opens or shorts to ground.

Step 3: Voltage and Signal Verification Reconnect the battery and use a multimeter or oscilloscope to verify CAN bus voltage. With ignition on and engine off, measure between CAN-High and ground (should read approximately 2.5-3.5V) and CAN-Low to ground (approximately 1.5-2.5V). The differential voltage between CAN-High and CAN-Low should fluctuate between 1.5-2.5V during active communication.

Step 4: ECM and Software Diagnostics Connect Hitachi diagnostic software (Dr.EX) or a compatible scan tool to retrieve detailed fault data and freeze frame information. Check for stored communication timeout errors and verify ECM firmware version. For used machines, consider that ECM capacitor aging may cause intermittent failures—bench testing the ECM or replacement may be necessary if all harness testing passes.

Step 5: Ground Circuit Verification Inspect and clean ground point G201 near the battery box. Measure resistance from ECM ground pin to battery negative—should be less than 0.5 ohms. Poor grounds are frequently overlooked on older excavators and cause numerous electrical anomalies.

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Disclaimer: This guide provides general troubleshooting information for Code 656-3. Always consult the Hitachi EX200-3 service manual for model-specific procedures and specifications. If you lack experience with electronic diagnostics or CAN bus systems, consult a certified heavy equipment technician to prevent further damage to control modules.