Komatsu PC750LC-7 Fault Code E205: Complete Diagnostic Guide

What is Komatsu PC750LC-7 Fault Code E205?

Fault Code E205 indicates a malfunction in the hydraulic pump control system, specifically related to the pump flow control solenoid valve circuit. This code triggers when the Engine Control Module (ECM) detects an abnormal voltage or current signal from the pump control solenoid, which regulates hydraulic flow based on operational demands.

In the PC750LC-7, this system is critical for maintaining optimal hydraulic performance and fuel efficiency. The proportional solenoid valve modulates pump displacement to match load requirements. When E205 appears, the excavator may default to a fixed displacement mode, significantly impacting productivity and increasing fuel consumption on this 400+ horsepower machine.

Common Symptoms

When Code E205 is active, operators typically experience:

• Reduced hydraulic power across all functions (boom, arm, bucket, and swing operations feel sluggish)
• Warning light illumination on the monitor panel with possible audible alarm
• Increased engine RPM without corresponding hydraulic speed due to pump control failure
• Erratic hydraulic response or inconsistent flow during combined operations
• Derate mode activation limiting engine power to protect the hydraulic system

Potential Causes

The most common technical causes for E205 on used PC750LC-7 excavators include:

• Solenoid valve coil failure due to heat exposure or internal short/open circuit (resistance typically should read 8-12 ohms)
• Wiring harness damage at known rub points near the main pump mounting area where vibration causes insulation wear
• Corroded or loose connector pins at the pump solenoid harness connection (C-series connectors are prone to moisture intrusion)
• ECM internal driver circuit failure (less common but possible on high-hour machines)
• Voltage supply issues from the main power harness or poor grounding connections

How to Troubleshoot and Fix Code E205

Step 1: Visual Inspection Begin by inspecting the pump control solenoid connector located on the main hydraulic pump. Check for corrosion, bent pins, or moisture. On used excavators, this connector often shows green corrosion due to seal degradation. Clean contacts with electrical cleaner and dielectric grease.

Step 2: Electrical Testing Using a digital multimeter, measure solenoid coil resistance (should be 8-12 ohms at room temperature). Then check for supply voltage at the connector with ignition on (should read approximately 12V). Verify ground continuity to the ECM (less than 1 ohm resistance).

Step 3: Harness Inspection Trace the wiring harness from the pump to the ECM, paying special attention to areas where the harness contacts the frame or passes through grommets. Look for abraded insulation, a common issue on machines with 8,000+ hours.

Step 4: Component Replacement If testing confirms solenoid failure, replace the pump control solenoid valve assembly. Use genuine Komatsu parts (Part #: 702-21-55901 or equivalent) to ensure proper specifications. After replacement, clear codes using Komatsu diagnostic software (KOMTRAX) and perform a function test.

Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu service manual for your specific serial number and consider professional diagnosis for complex electrical issues or if you lack proper diagnostic equipment.