Komatsu PC750SE-7 Fault Code E956: Complete Diagnostic Guide

What is Komatsu PC750SE-7 Fault Code E956?

Fault Code E956 indicates a malfunction in the hydraulic pump control system, specifically related to the pump flow control solenoid valve circuit or its associated sensors. This code is triggered when the Electronic Control Module (ECM) detects an abnormal voltage, current draw, or response time from the pump control solenoid that regulates hydraulic flow distribution.

In the PC750SE-7, this system is critical for maintaining optimal hydraulic performance across all functions. The pump flow control solenoid adjusts displacement based on load demands, directly affecting fuel efficiency and operational responsiveness. When E956 activates, the machine typically enters a protective derate mode to prevent hydraulic system damage.

Common Symptoms

When Code E956 is active, operators typically experience:

• Reduced hydraulic power across all functions (boom, arm, bucket, swing)
• Illuminated warning lamp on the monitor panel with fault code display
• Sluggish or unresponsive controls, particularly under heavy load conditions
• Increased engine RPM without corresponding hydraulic speed (pump not responding to demand)
• Intermittent loss of auxiliary hydraulic functions or attachment performance issues

Potential Causes

The most common technical causes for E956 in used PC750SE-7 excavators include:

• Solenoid valve coil failure due to overheating or internal short circuits (common after 8,000+ hours)
• Wiring harness damage at known rub points near the pump mounting bracket and main frame pivot
• Corroded or loose connector pins at the pump solenoid harness connection (C-207 connector)
• ECM internal driver circuit failure affecting solenoid control output
• Contaminated hydraulic oil causing solenoid valve spool sticking or mechanical binding
• Voltage supply issues from the main power harness or ground connection degradation

How to Troubleshoot and Fix Code E956

Step 1: Visual Inspection Begin by inspecting the pump flow control solenoid and its wiring harness for obvious damage. On used excavators, check for harness wear at the pump mounting area and frame articulation points. Examine connector C-207 for corrosion, bent pins, or oil contamination.

Step 2: Electrical Testing Using a digital multimeter, measure solenoid coil resistance (should be 3-7 ohms typically). Check supply voltage at the connector with ignition on (should read 24V). Perform a voltage drop test on ground circuits—readings above 0.5V indicate poor grounding requiring cleaning or replacement.

Step 3: Functional Testing Connect Komatsu KOMTRAX diagnostic software or compatible scan tool. Monitor solenoid command values versus actual response. Perform active tests to energize the solenoid while monitoring current draw (typical range: 2-4 amps). Abnormal readings indicate solenoid replacement needed.

Step 4: Component Replacement If testing confirms solenoid failure, replace with genuine Komatsu parts and verify hydraulic oil cleanliness (ISO 18/16/13 or better). Clear codes and perform calibration procedures through diagnostic software.

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Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu service manual for your specific serial number and consider professional technician assistance for complex hydraulic system repairs.