Komatsu PC750SE-7 Fault Code E115: Complete Diagnostic Guide

What is Komatsu PC750SE-7 Fault Code E115?

Fault Code E115 indicates a malfunction in the hydraulic pump control system, specifically related to the pump flow control solenoid valve circuit. This code triggers when the Electronic Control Module (ECM) detects an abnormal voltage or current reading from the pump control solenoid, which regulates hydraulic flow based on operational demands.

In the PC750SE-7 model, this system is critical for maintaining optimal hydraulic performance and fuel efficiency. The pump flow control directly affects attachment speed, digging force, and overall machine responsiveness. When E115 appears, the ECM may limit hydraulic output to prevent potential damage.

Common Symptoms

When Code E115 is active, operators typically experience:

• Reduced hydraulic power across all functions (boom, arm, bucket, and swing movements become sluggish)
• Amber warning light illuminated on the monitor panel with fault code display
• Engine derate mode may activate, limiting RPM to protect the hydraulic system
• Inconsistent attachment response, particularly during combined operations
• Increased fuel consumption due to inefficient pump operation

Potential Causes

The most common technical reasons for E115 on used PC750SE-7 excavators include:

• Solenoid valve coil failure due to age-related insulation breakdown or overheating
• Wiring harness damage at known rub points near the pump mounting bracket and along the main boom
• Corroded or loose connector pins at the pump control solenoid (C-connector series)
• ECM internal fault affecting the solenoid driver circuit
• Voltage supply issues from the main power harness or ground connections
• Contaminated hydraulic oil causing solenoid valve sticking or mechanical binding

How to Troubleshoot and Fix Code E115

Step 1: Visual Inspection Begin by inspecting the pump control solenoid connector located on the main hydraulic pump assembly. Check for corrosion, bent pins, or oil contamination. On used excavators, this connector frequently shows wear from vibration and heat exposure. Clean contacts with electrical contact cleaner and ensure proper seating.

Step 2: Electrical Testing Using a digital multimeter, measure solenoid coil resistance. Disconnect the solenoid connector and test between the two solenoid terminals. Typical resistance should be 3-7 ohms (consult service manual for exact specifications). Also check for short to ground by testing each terminal to the solenoid body—readings should show infinite resistance.

Step 3: Voltage Supply Check With ignition on and engine running, backprobe the harness connector to verify supply voltage (should read approximately 24V DC). If voltage is absent or fluctuating, trace the harness back toward the ECM, checking for damaged wires at common wear points: behind the cab, along the swing bearing, and near hydraulic hoses.

Step 4: Solenoid Function Test If electrical values are correct, the solenoid valve itself may be mechanically stuck. Remove the solenoid and inspect for metal debris or varnish buildup. For used machines, hydraulic contamination is common. Replace hydraulic filters and flush the system if contamination is evident.

Step 5: ECM Verification If all external components test normally, the ECM driver circuit may be faulty. This requires Komatsu diagnostic software (KOMTRAX or PC-based tools) to perform output tests and verify ECM functionality. Consider ECM replacement only after eliminating all other causes.

Critical Note for Used Equipment: Always inspect harness routing and protection thoroughly. The PC750SE-7's pump harness passes through high-vibration areas where insulation wear creates intermittent faults that are difficult to diagnose.

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Disclaimer: This guide provides general diagnostic procedures. Always consult the official Komatsu service manual for your specific machine serial number. Complex electrical or hydraulic repairs should be performed by certified technicians with proper diagnostic equipment.