Komatsu PC800-7 Fault Code E956: Complete Diagnostic Guide

What is Komatsu PC800-7 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 PC800-7, this system is critical for maintaining optimal hydraulic pressure and flow to all work functions. The pump flow control solenoid modulates pump displacement based on operator demand and load conditions. When E956 appears, the machine may enter a protective derate mode to prevent hydraulic system damage, significantly impacting productivity on job sites.

Common Symptoms

When Code E956 is active, operators typically experience:

• Reduced hydraulic power across all functions (boom, arm, bucket, swing)
• Warning light illumination on the monitor panel with fault code display
• Sluggish or unresponsive controls, particularly under heavy load conditions
• Intermittent loss of hydraulic function that may temporarily resolve then return
• Increased engine RPM without corresponding hydraulic performance (pump not responding to demand signals)

Potential Causes

The most common technical causes for E956 in 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 hydraulic pump mounting area
• Corroded or loose connector pins at the pump control solenoid (especially in machines operating in wet/corrosive environments)
• ECM voltage supply issues providing incorrect reference voltage to the solenoid circuit
• Internal solenoid valve contamination from degraded hydraulic fluid or metal particles
• Failed pump control sensor providing incorrect feedback to the ECM

How to Troubleshoot and Fix Code E956

Step 1: Visual Inspection Begin by inspecting the pump control solenoid connector and wiring harness for obvious damage. On used excavators, check for harness wear where cables contact the pump housing or frame rails. Look for oil contamination on connectors indicating seal failures.

Step 2: Electrical Testing Using a digital multimeter, measure solenoid coil resistance (typically 10-30 ohms for Komatsu systems). Check for supply voltage at the connector with ignition on (should read 12-24V depending on circuit design). Verify ground circuit continuity to the ECM.

Step 3: Solenoid Function Test With Komatsu diagnostic software (KOMTRAX or compatible scan tool), perform an active test of the solenoid valve. Listen for audible clicking and measure current draw (typically 0.5-2.0 amps). Compare readings to factory specifications.

Step 4: Hydraulic System Check Inspect hydraulic fluid condition and filter status. Contaminated fluid can cause internal solenoid valve sticking. On high-hour used machines, consider removing the solenoid for bench testing and cleaning.

Step 5: Component Replacement If testing confirms solenoid failure, replace with genuine Komatsu parts when possible. After installation, clear codes, perform calibration procedures, and cycle all hydraulic functions under load to verify repair.

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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 hydraulic system repairs. Improper diagnosis can lead to costly component damage.