What is Hitachi ZX270-3 Fault Code 655-3?

Fault Code 655-3 on the Hitachi ZX270-3 excavator indicates a malfunction in the Engine Control Module (ECM) related to injector circuit abnormalities, specifically an open circuit or high resistance detected in injector #3. This diagnostic trouble code (DTC) is triggered when the ECM detects that the electrical signal to the fuel injector on cylinder three is outside the manufacturer's specified parameters, typically indicating a wiring issue, connector problem, or failed injector solenoid.

This code is critical for the ZX270-3's Isuzu engine performance because precise fuel delivery directly affects combustion efficiency, power output, and emissions compliance. When injector #3 fails to receive proper electrical signals, the engine cannot maintain optimal fuel atomization, leading to rough operation and potential long-term damage to the cylinder.

Common Symptoms

• Rough idle or engine misfiring, particularly noticeable at low RPM or during warm-up cycles
• Loss of power during digging operations or under heavy hydraulic load
• Black or white exhaust smoke indicating incomplete combustion in the affected cylinder
• Check Engine light illuminated on the instrument panel with reduced engine performance
• Increased fuel consumption as the ECM attempts to compensate for the malfunctioning injector

Potential Causes

The most common technical causes for Code 655-3 on used ZX270-3 excavators include:

• Damaged or corroded wiring harness between the ECM and injector #3, especially at known rub points near the engine block mounting brackets
• Failed injector solenoid coil on cylinder #3 due to heat cycling and age-related degradation
• Corroded or loose electrical connectors at the injector or ECM, particularly in machines with high operating hours in wet or corrosive environments
• Internal ECM driver circuit failure affecting only the #3 cylinder output
• Chafed harness insulation where the engine harness contacts the valve cover or fuel lines during engine vibration

How to Troubleshoot and Fix Code 655-3

Step 1: Visual Inspection Begin by inspecting the wiring harness from the ECM to injector #3. On used excavators, pay special attention to areas where the harness contacts metal surfaces or passes near the exhaust manifold. Look for abraded insulation, melted wires, or corroded connectors.

Step 2: Electrical Testing Using a digital multimeter, disconnect the injector #3 connector and measure the solenoid resistance. Specification should be approximately 0.3-0.5 ohms at room temperature. Next, check for continuity in the wiring harness between the ECM connector and the injector connector. Any reading above 1 ohm indicates excessive resistance.

Step 3: Power and Ground Verification With the key on and engine off, verify that the injector receives proper voltage (typically 12-24V depending on system design) from the ECM during cranking. Use a breakout harness or back-probe the connector to avoid damaging terminals.

Step 4: Component Replacement If wiring checks pass, replace injector #3. For used excavators with over 8,000 hours, consider replacing all injector O-rings and copper washers during this service to prevent future leaks. If the injector tests good, the ECM may have an internal driver failure requiring replacement or professional reprogramming.

Step 5: Clear Codes and Retest After repairs, use Hitachi Dr.EX diagnostic software or equivalent scan tool to clear fault codes. Operate the machine under load for 20-30 minutes and monitor for code recurrence.

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Disclaimer: This guide provides general troubleshooting information. Always consult the Hitachi ZX270-3 service manual and consider professional diagnostic assistance for complex electrical issues. Improper repairs may cause engine damage or safety hazards.