Komatsu PC120-6 Fault Code E103: Complete Diagnostic Guide

What is Komatsu PC120-6 Fault Code E103?

Fault Code E103 indicates a hydraulic pump pressure sensor malfunction or abnormal signal in the main hydraulic system. This code is triggered when the Electronic Control Module (ECM) detects voltage readings outside the specified range (typically 0.5-4.5V) from the main pump pressure sensor, which monitors hydraulic system pressure for optimal performance and component protection.

This fault is critical for the PC120-6 because the hydraulic pressure sensor provides essential data for the machine's load-sensing system. When this sensor fails, the ECM cannot properly regulate pump output, potentially causing reduced digging force, erratic hydraulic response, and increased fuel consumption. In severe cases, the machine may enter a derate mode to prevent hydraulic system damage.

Common Symptoms

• Warning light illuminated on the instrument cluster, often accompanied by audible alarm
• Noticeably reduced hydraulic power across all functions (boom, arm, bucket, swing)
• Erratic or inconsistent response when operating multiple hydraulic functions simultaneously
• Engine RPM fluctuation during loaded operations due to improper pump compensation
• Intermittent loss of hydraulic power, especially during cold starts or after extended operation

Potential Causes

The most common causes for E103 in used PC120-6 excavators include:

• Pressure sensor failure due to internal diaphragm wear or contamination from hydraulic fluid breakdown
• Damaged or corroded wiring harness between the sensor and ECM, particularly at connector points near the pump
• Connector corrosion at the sensor plug caused by hydraulic oil mist or water intrusion
• Hydraulic oil contamination causing sensor port blockage or sensor element degradation
• ECM voltage supply issues providing incorrect reference voltage to the sensor circuit
• Physical damage to sensor mounting or severed wiring from vibration wear at known rub points near the main pump

How to Troubleshoot and Fix Code E103

Step 1: Visual Inspection Begin by inspecting the pressure sensor located on the main hydraulic pump. Check for physical damage, oil leaks around the sensor, or loose mounting. Examine the wiring harness from sensor to ECM for abraded insulation, especially where it contacts metal surfaces or hydraulic lines—a common failure point on used machines.

Step 2: Electrical Testing Using a digital multimeter, measure the sensor's output voltage with the ignition on, engine off. Reference voltage should read approximately 0.5-1.0V at zero pressure. Check connector pins for corrosion and measure resistance through the harness (should be less than 5 ohms). Test ECM supply voltage at the sensor connector (should be 5V ±0.25V).

Step 3: Dynamic Testing Start the engine and monitor sensor voltage while operating hydraulics. Voltage should increase proportionally with load (up to 4.5V at maximum pressure). Erratic readings indicate sensor failure; stable low/high readings suggest wiring issues or ECM problems.

Step 4: Component Replacement For used excavators, replace the pressure sensor first, as they commonly fail after 5,000+ hours. Clean all connector contacts with electrical contact cleaner before reconnection. If issues persist, inspect hydraulic oil quality and consider harness replacement, particularly if previous repairs show evidence of temporary fixes.

Disclaimer: This guide provides general diagnostic procedures. Always consult the official Komatsu service manual and consider professional assistance for complex electrical diagnostics or hydraulic system repairs.