Komatsu PC138USLC-2 Fault Code E-6: Meaning and Fix Guide

What is Komatsu PC138USLC-2 Fault Code E-6?

Fault Code E-6 indicates a malfunction in the hydraulic oil temperature sensor circuit or an abnormal hydraulic oil temperature reading on the Komatsu PC138USLC-2 excavator. This code is triggered when the Engine Control Module (ECM) detects an out-of-range signal from the hydraulic oil temperature sensor, typically either an open circuit, short circuit, or readings exceeding normal operating parameters (typically 105-110°C/221-230°F).

The hydraulic oil temperature sensor is critical for this excavator's performance monitoring system. It protects the hydraulic pump, control valves, and cylinder seals from thermal damage by alerting operators to overheating conditions. In the PC138USLC-2, excessive hydraulic temperatures can lead to reduced hydraulic efficiency, accelerated component wear, and potential system failure.

Common Symptoms

• Warning lamp illuminated on the monitor panel with "E-6" displayed
• Reduced hydraulic response or sluggish attachment operation
• Automatic engine derate preventing high RPM operation to protect hydraulic components
• Audible warning buzzer sounding intermittently or continuously
• Hydraulic oil may feel excessively hot to touch near the hydraulic tank or return lines

Potential Causes

The E-6 code commonly appears due to several factors, particularly in used excavators:

• Faulty hydraulic oil temperature sensor (resistance drift due to age or contamination)
• Damaged or corroded wiring harness between sensor and ECM, especially at connector pins
• Wiring harness chafing near the hydraulic tank mounting bracket (known wear point on PC138USLC-2 models)
• Poor electrical connections at sensor connector due to moisture intrusion or corrosion
• Actual hydraulic overheating caused by restricted oil cooler, low oil level, or excessive hydraulic load
• ECM internal circuit failure (less common, but possible in high-hour machines)

How to Troubleshoot and Fix Code E-6

Step 1: Visual Inspection Locate the hydraulic oil temperature sensor on the hydraulic tank (typically near the return filter assembly). Inspect the sensor connector for corrosion, bent pins, or moisture. Check the wiring harness routing for signs of rubbing, particularly where it passes near metal brackets or the tank edge.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure resistance across its terminals. At room temperature (20°C/68°F), resistance should typically read 2,000-3,000 ohms. Check the wiring harness for continuity between sensor connector and ECM pins. Look for shorts to ground or open circuits.

Step 3: Verify Actual Temperature Use an infrared thermometer to measure actual hydraulic oil temperature at the tank. Compare with sensor reading using Komatsu diagnostic software (KOMTRAX Plus) or compatible scan tool. If actual temperature is normal but sensor reads high, replace the sensor.

Step 4: Connector and Harness Repair For used excavators, clean all connector pins with electrical contact cleaner. Apply dielectric grease to prevent future corrosion. Repair or reroute chafed harness sections using proper electrical tape and protective loom.

Disclaimer: This guide provides general troubleshooting steps. Always consult the official Komatsu service manual for your specific machine serial number and consider professional diagnostic assistance for complex electrical issues.