Komatsu HB205-1 Fault Code E-35: Complete Diagnostic Guide

What is Komatsu HB205-1 Fault Code E-35?

Fault Code E-35 on the Komatsu HB205-1 hybrid excavator indicates a malfunction in the swing motor resolver circuit, specifically detecting an abnormal signal or voltage irregularity in the swing motor's position feedback system. This code directly affects the hybrid system's ability to accurately monitor and control the swing motor's rotational position and speed.

The resolver is a critical rotary transformer that provides precise positional feedback to the hybrid control system ECU. Unlike standard excavators, the HB205-1's hybrid architecture relies on this resolver data to coordinate energy regeneration during swing deceleration and optimize power distribution between the diesel engine and electric motor-generator. When E-35 triggers, the machine's energy efficiency and swing performance become compromised, potentially forcing the system into a protective mode that limits hybrid functionality.

Common Symptoms

• Hybrid system warning lamp illuminates on the dashboard with possible error message display
• Reduced swing speed or jerky, inconsistent swing operation during rotation
• Loss of swing regeneration capability, resulting in decreased fuel efficiency and battery charging
• Audible alarm or beeping from the cab warning system during swing operations
• Machine may default to conventional mode, bypassing hybrid assist features entirely

Potential Causes

The E-35 code typically stems from electrical issues within the swing motor resolver circuit:

• Resolver connector corrosion at the swing motor assembly—common in used machines exposed to moisture, mud, and debris intrusion
• Damaged resolver wiring harness caused by rubbing against the swing bearing race or mounting brackets during thousands of rotation cycles
• Faulty resolver sensor internally due to bearing wear, coil deterioration, or magnetic component degradation
• Swing motor ECU communication failure from poor grounding points or corroded ECU connector pins
• Voltage supply issues to the resolver circuit (typically requires 5-8V reference voltage from the hybrid controller)
• Physical damage to the swing motor resolver housing from impact or improper removal during previous repairs

How to Troubleshoot and Fix Code E-35

Step 1: Visual Inspection and Connector Check Begin by accessing the swing motor resolver connector located on the swing motor assembly. Disconnect and carefully inspect for corrosion, bent pins, moisture intrusion, or oil contamination. Clean contacts with electrical contact cleaner and check connector locking mechanisms. On used excavators, this connector often shows green corrosion due to water ingress.

Step 2: Wiring Harness Continuity Testing Using a digital multimeter (DMM), perform continuity tests on all resolver wiring from the swing motor connector back to the hybrid control ECU. Check for opens, shorts to ground, or shorts between circuits. Pay special attention to harness routing near the swing bearing—this is a known wear point where insulation breaks down from constant flexing. Resistance should typically be less than 5 ohms for power/ground circuits.

Step 3: Resolver Signal and Voltage Verification With Komatsu diagnostic software (KOMTRAX or dealer-level diagnostics) connected, monitor live resolver output signals while manually rotating the swing structure. The resolver should produce sine and cosine wave signals that change smoothly with rotation. Check for the proper reference voltage supply (usually 5-8V DC) at the resolver power pin with the key on, engine off.

Step 4: Resolver Resistance Testing Disconnect the resolver and measure winding resistance between resolver terminals. Consult the Komatsu service manual for exact specifications, but typical resolver windings read between 50-200 ohms. Significant deviation indicates internal resolver failure requiring replacement.

Step 5: Ground Circuit Verification Check all grounding points in the swing motor circuit, particularly the swing motor case ground and ECU chassis grounds. Poor grounds cause erratic resolver signals. Clean ground contact surfaces to bare metal and verify less than 0.5 ohms resistance to battery negative.

For used excavators, always inspect for previous repair attempts, aftermarket wiring splices, or water damage in the swing pedestal area before replacing expensive components like the resolver or swing motor assembly.

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Disclaimer: This guide provides general diagnostic information for the Komatsu HB205-1 hybrid excavator. Always consult the official Komatsu service manual and consider professional diagnostic assistance from certified Komatsu technicians for complex hybrid system repairs. Improper diagnosis can lead to expensive component replacement and extended downtime.