Komatsu PC650LC-8R Fault Code E-27: Complete Diagnostic Guide

What is Komatsu PC650LC-8R Fault Code E-27?

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

The hydraulic oil temperature sensor is critical for the PC650LC-8R's performance management system. It monitors the operating temperature of the hydraulic fluid, allowing the ECM to adjust pump output, activate cooling fans, and prevent thermal damage to hydraulic components. When this sensor fails or provides incorrect data, 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 illuminated on the instrument panel, often accompanied by an audible alarm
• Reduced hydraulic performance or sluggish operation as the system enters protective mode
• Cooling fan running continuously at high speed, regardless of actual operating temperature
• Erratic temperature gauge readings on the monitor display, showing unusually high or low values
• Machine derate limiting engine RPM or hydraulic flow to protect components

Potential Causes

The most common technical causes for Code E-27 on used PC650LC-8R excavators include:

• Failed hydraulic oil temperature sensor due to age, thermal cycling, or internal component degradation
• Damaged wiring harness near the hydraulic tank, particularly at known rub points where the harness contacts frame members
• Corroded or loose connector pins at the sensor connection point, especially on machines operating in wet or corrosive environments
• Shorted sensor wiring caused by insulation breakdown from prolonged heat exposure
• ECM internal fault (rare) affecting the sensor input circuit
• Contaminated hydraulic oil causing sensor element fouling or coating

How to Troubleshoot and Fix Code E-27

Step 1: Visual Inspection Begin by locating the hydraulic oil temperature sensor (typically mounted on the hydraulic tank). Inspect the wiring harness from the sensor to the ECM for obvious damage, chafing, or oil contamination. On used excavators, pay special attention to harness routing near moving components or sharp edges where insulation wear commonly occurs.

Step 2: Connector and Resistance Testing Disconnect the sensor connector and inspect for corrosion, bent pins, or moisture intrusion. Using a digital multimeter, measure the sensor's resistance. At room temperature (20°C/68°F), resistance should typically read between 2,000-3,000 ohms (consult your service manual for exact specifications). Compare readings at different temperatures to verify proper sensor function.

Step 3: Circuit Voltage Testing With the sensor disconnected and ignition on, measure voltage at the harness connector. You should see approximately 5 volts on the signal wire (reference voltage from the ECM). If voltage is absent or incorrect, trace the wiring for breaks or shorts to ground.

Step 4: Sensor Replacement and Verification If the sensor tests faulty, replace it with a genuine Komatsu part to ensure proper calibration. After installation, clear the fault code using Komatsu diagnostic software (KOMTRAX) or a compatible scan tool. Operate the machine through a full warm-up cycle to verify the code doesn't return.

Critical Note for Used Equipment: Before replacing the sensor, thoroughly inspect all connector seals and apply dielectric grease to prevent future corrosion. Check hydraulic oil condition—contaminated oil can cause premature sensor failure.

---

Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu service manual for your specific machine serial number. If you're uncomfortable performing electrical diagnostics, contact a certified Komatsu technician to prevent further damage or safety hazards.