Komatsu PC800-7 Fault Code E957: Complete Diagnostic Guide

What is Komatsu PC800-7 Fault Code E957?

Fault Code E957 indicates a malfunction in the hydraulic pump control system, specifically related to the main pump regulator solenoid circuit or its associated control signals. This code is triggered when the Electronic Control Module (ECM) detects an abnormal voltage, current draw, or response time from the pump regulator solenoid valve that controls hydraulic flow and pressure.

In the PC800-7, this system is critical because the pump regulator directly manages engine load matching and hydraulic efficiency. When E957 appears, the machine may enter a protective derate mode to prevent damage to the hydraulic system or engine. This fault is particularly significant in used excavators where electrical connections and solenoid components experience cumulative wear from thousands of operating hours in harsh environments.

Common Symptoms

• Reduced hydraulic power across all functions, with noticeably slower boom, arm, or swing speeds
• Engine RPM fluctuations or inability to maintain consistent power under load
• Warning light activation on the monitor panel, often accompanied by an audible alarm
• Erratic hydraulic response where the machine may surge or hesitate during combined operations
• Automatic engine derate limiting maximum RPM to protect the drivetrain

Potential Causes

The most common technical causes for E957 in used PC800-7 excavators include:

• Solenoid valve failure due to internal coil degradation or contaminated hydraulic oil causing stuck spools
• 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 regulator harness connection (C-series connectors are vulnerable to moisture intrusion)
• ECM voltage supply issues from failing relays or degraded ground connections at the controller chassis mount
• Hydraulic contamination causing mechanical binding of the regulator piston, increasing electrical load beyond normal parameters

How to Troubleshoot and Fix Code E957

Step 1: Visual Inspection Begin by inspecting the pump regulator solenoid connector for corrosion, bent pins, or oil contamination. On used excavators, check the wiring harness routing from the ECM to the main pump—look specifically for abrasion points where the harness contacts the pump housing or frame rails.

Step 2: Electrical Testing Using a digital multimeter, measure solenoid resistance (typically 8-15 ohms for PC800-7 regulators) and check for supply voltage (should be 12V with key on). Test the ground circuit for resistance below 1 ohm. Employ Komatsu KOMTRAX or compatible diagnostic software to monitor real-time solenoid command signals versus actual response.

Step 3: Component Testing If electrical values are correct, perform a hydraulic pressure test at the pump regulator port to verify mechanical operation. Replace the solenoid valve if resistance is out of spec or if mechanical binding is evident. For used machines, always replace connector seals and apply dielectric grease to prevent future corrosion.

Step 4: System Verification After repairs, clear codes, run the machine through full hydraulic cycles, and monitor for code recurrence. Check hydraulic oil condition—contaminated oil often causes repeat failures.

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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 electrical or hydraulic repairs.