Hitachi ZH200-5A Fault Code P1655: Technical Guide

What is Hitachi ZH200-5A Fault Code P1655?

Fault Code P1655 on the Hitachi ZH200-5A excavator indicates a malfunction in the Engine Control Module (ECM) internal circuit, specifically related to the ECM's internal processor or memory system failure. This diagnostic trouble code (DTC) signals that the ECM has detected an abnormality in its own internal operations, affecting its ability to properly manage engine functions and communicate with other systems.

This code is critical because the ECM serves as the brain of the engine management system, controlling fuel injection timing, emission systems, and overall engine performance. When P1655 activates, the excavator's engine may enter a protective derate mode to prevent further damage, significantly impacting jobsite productivity on this reliable Isuzu-powered hydraulic excavator.

Common Symptoms

When fault code P1655 is active on your Hitachi ZH200-5A, operators typically experience:

• Check Engine Light or Malfunction Indicator Lamp (MIL) illuminated on the dashboard
• Engine operating in limp mode or derate with reduced power output (typically 30-50% power loss)
• Intermittent engine stalling or rough idling, particularly during cold starts
• Inability to reach full RPM or throttle response delays
• Communication errors between the ECM and display monitor, showing incomplete diagnostic data

Potential Causes

The most common technical causes for P1655 on used ZH200-5A excavators include:

• ECM internal component failure due to age, heat cycling, or voltage spikes from electrical system issues
• Corroded or damaged ECM connectors from moisture intrusion, especially on machines operating in wet or coastal environments
• Main wiring harness damage near the ECM mounting location, a known wear point on ZH200 series machines
• Faulty or degraded main power supply relay causing voltage fluctuations to the ECM
• Software corruption within the ECM memory from previous improper shutdowns or battery disconnections
• Ground connection failure at ECM mounting points due to corrosion or loosened bolts

How to Troubleshoot and Fix Code P1655

Step 1: Verify Code and Check Battery Voltage Using Hitachi diagnostic software (Dr.EX or compatible scan tool), confirm P1655 is active and not a stored historical code. Check battery voltage with a digital multimeter—should read 24-26V with engine off, 27-28V running. Low voltage can cause false ECM errors.

Step 2: Inspect ECM Connections and Grounds On used excavators, thoroughly inspect the ECM connector (typically located near the operator cab or under the right side cover). Look for corrosion, bent pins, or moisture in connector housings. Clean contacts with electrical contact cleaner and apply dielectric grease. Verify all ground connections at the ECM mounting bracket are tight and corrosion-free.

Step 3: Check Main Power Supply and Harness Trace the main power harness from the battery to the ECM, inspecting for chafing, rubbing, or damaged insulation, particularly where the harness passes through bulkheads. Test the main relay function and measure voltage drop across connections (should be less than 0.2V).

Step 4: ECM Evaluation and Replacement If all connections and power supply check good, the ECM itself may have internal failure. Before replacement, attempt to clear the code and monitor for recurrence—some intermittent issues resolve after connector cleaning. For confirmed ECM failure, replacement with a genuine Hitachi ECM or verified remanufactured unit is necessary, followed by proper programming with machine-specific parameters.

Disclaimer: This guide provides general troubleshooting information for experienced technicians. Always consult the official Hitachi ZH200-5A service manual and consider professional diagnostic services for complex electrical issues. Improper ECM handling or installation can cause additional system damage.