Komatsu PC800-7 Fault Code E955: Complete Diagnostic Guide

What is Komatsu PC800-7 Fault Code E955?

Fault Code E955 indicates a malfunction in the hydraulic pump control system, specifically related to the pump flow control solenoid valve circuit or its associated wiring harness. This code is triggered when the Electronic Control Module (ECM) detects an abnormal voltage or resistance reading from the pump control solenoid, which directly regulates hydraulic flow and pressure distribution throughout the machine.

For the PC800-7, this is a critical fault because the hydraulic pump control system manages the variable displacement pump that powers all hydraulic functions. When E955 appears, the ECM may limit pump output to protect the system, resulting in reduced machine performance and potential operational shutdown.

Common Symptoms

When Code E955 is active on your Komatsu PC800-7, operators typically experience:

• Reduced hydraulic power across all functions (boom, arm, bucket, swing, and travel)
• Warning light illumination on the monitor panel with accompanying fault code display
• Machine entering derate mode, limiting engine RPM and hydraulic flow
• Erratic hydraulic response or inconsistent cycle times during operation
• Complete loss of hydraulic function in severe cases where the ECM enters protective shutdown mode

Potential Causes

The most common technical causes for E955 on used PC800-7 excavators include:

• Solenoid valve coil failure due to age, overheating, or internal short circuits
• Wiring harness damage at known rub points near the pump mounting area or along the main chassis harness
• Connector corrosion at the pump control solenoid connector, especially on machines operating in wet or coastal environments
• ECM internal fault affecting the solenoid driver circuit (less common but possible on high-hour machines)
• Voltage supply issues from damaged power distribution harnesses or poor ground connections
• Previous repair attempts using incorrect solenoid specifications or improper wiring modifications

How to Troubleshoot and Fix Code E955

Step 1: Visual Inspection Begin by inspecting the pump control solenoid and its wiring harness for obvious damage. On used excavators, check for harness chafing where the wiring passes near the pump mounting bracket and hydraulic lines. Examine all connectors for corrosion, bent pins, or moisture intrusion.

Step 2: Electrical Testing Using a digital multimeter, disconnect the solenoid connector and measure coil resistance. Typical specifications for the PC800-7 pump solenoid range from 10-15 ohms. Also check for voltage supply at the connector with the ignition on (should read approximately 12-24V depending on system design). Test for continuity between the solenoid ground and chassis ground.

Step 3: Advanced Diagnostics Connect Komatsu diagnostic software (KOMTRAX Plus or equivalent) to monitor real-time solenoid command signals from the ECM. Compare commanded versus actual current flow. If the ECM commands proper voltage but the solenoid doesn't respond, replace the solenoid valve. If no command signal exists, investigate ECM wiring or consider ECM failure.

Step 4: Repair and Verification For used machines, always inspect harness routing after repairs to prevent future wear. Replace damaged sections with proper gauge wire and use dielectric grease on all connectors. Clear the fault code and perform a complete hydraulic function test under load.

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Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu service manual for your specific machine serial number and consider professional assistance for complex electrical diagnostics or ECM-related issues.