Komatsu PC850SE-8R Fault Code E-27: Complete Diagnostic Guide

What is Komatsu PC850SE-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 temperature values from the hydraulic oil temperature sensor.

The hydraulic oil temperature sensor is critical for the PC850SE-8R's performance management system. It monitors the operating temperature of the hydraulic fluid, allowing the ECM to adjust pump output, implement protective derating, and prevent catastrophic damage to hydraulic components. When this sensor fails or provides incorrect data, the machine cannot properly regulate hydraulic system performance, potentially leading to overheating or inefficient operation.

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 attachment response, especially during warm-up
• Automatic engine derate or power reduction mode to protect hydraulic components
• Inaccurate or erratic hydraulic temperature gauge readings on the monitor display
• Machine may enter limp mode preventing operation until the fault is addressed

Potential Causes

The most common technical causes for E-27 on used PC850SE-8R excavators include:

• Faulty hydraulic oil temperature sensor due to age-related degradation or thermal cycling damage
• Damaged wiring harness or corroded connectors, particularly at harness routing points near the hydraulic tank where vibration and heat exposure are highest
• Open or short circuit in the sensor signal wire between the sensor and ECM
• Contaminated or corroded sensor connector pins from hydraulic fluid leaks or moisture intrusion
• ECM internal fault (less common) affecting the temperature sensor input circuit
• Incorrect sensor resistance values due to internal element failure

How to Troubleshoot and Fix Code E-27

Step 1: Visual Inspection Begin by locating the hydraulic oil temperature sensor, typically mounted on or near the hydraulic oil tank. Inspect the sensor connector for corrosion, bent pins, or hydraulic oil contamination. On used excavators, check the wiring harness routing for signs of chafing, especially where it contacts frame members or passes near hot components.

Step 2: Electrical Testing Disconnect the sensor connector and use a digital multimeter to measure sensor resistance. Compare readings against Komatsu specifications (typically 200-400 ohms at 20°C, varying with temperature). Check for continuity between the sensor terminals and ground—any continuity indicates a short circuit requiring sensor replacement.

Step 3: Circuit Verification With the sensor disconnected, measure voltage at the harness connector. You should see approximately 5 volts reference voltage from the ECM. Check circuit resistance between the harness connector and ECM pins. Resistance above 5 ohms suggests damaged wiring requiring repair or replacement.

Step 4: Component Replacement If sensor and wiring test within specifications, use Komatsu diagnostic software (KOMTRAX) to monitor live sensor data. Replace the sensor if readings are erratic or out of range. For used machines, always apply dielectric grease to connector pins during reassembly to prevent future corrosion.

Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu service manual for your specific serial number and consider professional diagnosis for complex electrical issues or if you lack proper diagnostic equipment.