Komatsu PC800-8R Fault Code E-27: Complete Diagnostic Guide

What is Komatsu PC800-8R Fault Code E-27?

Fault Code E-27 on the Komatsu PC800-8R 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 an out-of-range signal from the hydraulic oil temperature sensor.

This fault is critical for the PC800-8R's performance because the hydraulic oil temperature directly affects system efficiency, component longevity, and operational safety. The ECM uses temperature data to regulate hydraulic pump output, prevent overheating damage, and protect seals and hoses from thermal degradation. Ignoring this code can lead to catastrophic hydraulic system failure or reduced machine productivity.

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 boom, arm, and bucket movements due to ECM derate mode
• Inaccurate temperature gauge readings showing either extremely high or low values (or no reading at all)
• Machine may enter limp mode, limiting engine RPM and hydraulic flow to prevent potential damage
• Intermittent code activation during cold starts or after extended operation, indicating sensor degradation

Potential Causes

The most common technical causes for E-27 on used PC800-8R excavators include:

• Faulty hydraulic oil temperature sensor due to age-related failure or contamination exposure
• Damaged wiring harness at known rub points near the hydraulic tank or along the chassis frame rails
• Corroded or loose connector pins at the sensor plug, especially on machines operating in wet or coastal environments
• Shorted sensor ground wire caused by harness chafing against metal surfaces
• ECM internal fault (rare, but possible in high-hour machines)
• Actual hydraulic system overheating due to clogged coolers, low oil levels, or excessive ambient temperatures

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 for visible damage, abrasion, or oil contamination. Check connector pins for corrosion, bent terminals, or moisture intrusion—common issues in used excavators.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure its resistance at ambient temperature (typically 2,000-3,000 ohms at 20°C, but verify against Komatsu specifications). Test for continuity between sensor terminals and ground to identify shorts. Check supply voltage at the connector (usually 5V reference from ECM).

Step 3: Harness and ECM Verification Inspect harness routing for wear points where cables contact frame members—a notorious issue on PC800 models. Use Komatsu diagnostic software (KOMTRAX Plus) to monitor live sensor data and verify ECM communication. If sensor and wiring test correctly but the code persists, suspect ECM calibration issues or internal faults.

Step 4: Component Replacement Replace the temperature sensor if resistance values are out of specification. For used machines, always apply dielectric grease to connectors and secure harnesses away from moving components to prevent future failures.

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Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu service manual for your specific machine serial number and seek professional assistance from certified technicians for complex electrical diagnostics or ECM programming.