Komatsu PC650-8R Fault Code E-27: Complete Diagnostic Guide

What is Komatsu PC650-8R 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. This code is triggered when the Electronic Control Module (ECM) detects either an open circuit, short circuit, or out-of-range signal from the hydraulic oil temperature sensor located in the main hydraulic tank.

For the PC650-8R, this sensor is critical because it monitors hydraulic fluid temperature to prevent system damage and optimize performance. The ECM uses this data to adjust pump output, activate cooling fans, and protect hydraulic components from overheating. When E-27 appears, the machine may enter a protective derate mode to prevent catastrophic hydraulic system failure.

Common Symptoms

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

• Warning light illumination on the monitor panel with accompanying audible alarm
• Reduced hydraulic performance or sluggish boom/arm/bucket movements as the system enters protective mode
• Inaccurate temperature readings displayed on the monitor (showing extremely high or low values like -40°C or 150°C)
• Cooling fan running continuously at maximum speed regardless of actual oil temperature
• Machine may limit engine RPM or hydraulic flow to protect components

Potential Causes

The most common technical causes for E-27 on used PC650-8R excavators include:

• Faulty hydraulic oil temperature sensor due to age-related degradation or contamination exposure
• Damaged wiring harness between the sensor and ECM, particularly at known rub points near the hydraulic tank mounting bracket
• Corroded or loose connector pins at the sensor plug (common in machines exposed to moisture or harsh environments)
• Short circuit to ground caused by chafed insulation on sensor wiring
• ECM internal fault (rare, but possible in high-hour machines)
• Contaminated hydraulic oil causing sensor element fouling

How to Troubleshoot and Fix Code E-27

Step 1: Visual Inspection Begin by inspecting the hydraulic oil temperature sensor located on the main hydraulic tank. Check the connector for corrosion, bent pins, or oil contamination. On used excavators, examine the wiring harness for signs of rubbing against the tank or frame—this is a common failure point on the PC650 series.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure its resistance. A typical thermistor-type sensor should read approximately 2,000-3,000 ohms at 20°C (consult your service manual for exact specifications). Check for continuity in the harness between the sensor connector and ECM. Measure voltage supply from the ECM (typically 5V reference voltage).

Step 3: Component Replacement If the sensor tests out-of-specification or the harness shows damage, replace the faulty component. For used machines, always apply dielectric grease to connectors during reassembly to prevent future corrosion. Clear the code using Komatsu diagnostic software (KOMTRAX) or a compatible scan tool and verify proper operation.

Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu service manual for your specific machine serial number and seek professional assistance for complex repairs.