Komatsu PC800LC-8R Fault Code E-27: Complete Diagnostic Guide

What is Komatsu PC800LC-8R Fault Code E-27?

Fault Code E-27 indicates a malfunction in the hydraulic oil temperature sensor circuit or an abnormal hydraulic oil temperature reading in the Komatsu PC800LC-8R excavator. This code is triggered when the Electronic Control Module (ECM) detects either an open circuit, short circuit, or implausible temperature signal from the hydraulic oil temperature sensor.

The hydraulic system in the PC800LC-8R operates under extreme pressures and temperatures, making accurate temperature monitoring critical. This sensor provides essential data to the ECM for controlling cooling fan speed, preventing thermal damage, and maintaining optimal hydraulic fluid viscosity. When E-27 appears, the machine may enter a protective mode to prevent catastrophic hydraulic system failure.

Common Symptoms

When Code E-27 is active, operators typically experience:

• Warning light illuminated on the monitor panel, often accompanied by an audible alarm
• Reduced hydraulic performance or sluggish operation as the system enters derate mode
• Cooling fan running continuously at maximum speed regardless of actual temperature
• Erratic temperature gauge readings on the display, showing unrealistic values (extremely high or low)
• Machine shutdown in severe cases where the ECM cannot verify safe operating temperatures

Potential Causes

The most common technical causes for E-27 in used PC800LC-8R excavators include:

• Damaged or corroded sensor connector at the hydraulic tank, especially common in machines operating in wet or corrosive environments
• Failed hydraulic oil temperature sensor due to age-related degradation or thermal cycling stress
• Wiring harness damage along the routing path from the sensor to the ECM, particularly at flex points near the swing bearing
• Contaminated hydraulic oil causing sensor element fouling or coating
• ECM internal fault or corrupted calibration data (less common but possible in high-hour machines)
• Poor ground connections at the sensor mounting point or ECM chassis ground

How to Troubleshoot and Fix Code E-27

Step 1: Visual Inspection Begin by locating the hydraulic oil temperature sensor on the hydraulic tank (typically mounted on the side or top). Inspect the sensor connector for corrosion, oil contamination, bent pins, or moisture intrusion. Check the wiring harness for chafing, cuts, or damage along its entire length, paying special attention to areas where the harness passes through bulkheads or near moving components.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure its resistance at various temperatures (consult Komatsu specifications, typically 200-300 ohms at 20°C). Check for continuity in the wiring from the sensor connector to the ECM. Measure voltage supply at the sensor connector with the key on (should be approximately 5V reference voltage). Any readings outside specifications indicate sensor failure or wiring issues.

Step 3: Advanced Diagnostics Connect Komatsu diagnostic software (KOMTRAX Plus or equivalent) to view live sensor data and verify the ECM is receiving plausible signals. For used excavators, remove and physically inspect the sensor for carbon buildup, corrosion, or physical damage to the sensing element. Check hydraulic oil condition—contaminated or degraded oil can affect sensor accuracy.

Step 4: Repair and Verification Replace faulty components using genuine Komatsu parts when possible. Clean all connector terminals with electrical contact cleaner and apply dielectric grease. After repairs, clear the fault code, operate the machine through a complete warm-up cycle, and verify the code does not return. Monitor hydraulic oil temperature readings for accuracy.

---

Disclaimer: This guide provides general diagnostic information for Code E-27. Hydraulic and electrical system repairs should be performed by qualified technicians with appropriate training and tools. Always consult the official Komatsu service manual for your specific machine serial number and follow all safety procedures.