Komatsu PC110-7 Fault Code E-27: Complete Diagnostic Guide

What is Komatsu PC110-7 Fault Code E-27?

Fault Code E-27 on the Komatsu PC110-7 indicates a malfunction in the hydraulic oil temperature sensor circuit. This code specifically signals that the Engine Control Module (ECM) has detected an abnormal voltage reading from the temperature sensor monitoring the hydraulic oil in the main hydraulic system.

The hydraulic oil temperature sensor plays a critical role in this excavator's performance management system. When hydraulic oil becomes too hot, it loses viscosity and can cause serious damage to pumps, motors, and seals. The ECM relies on accurate temperature data to trigger warning systems and potentially limit machine operation to prevent catastrophic hydraulic system failure. On used PC110-7 models, this sensor and its wiring are particularly vulnerable to deterioration due to heat exposure and vibration stress over thousands of operating hours.

Common Symptoms

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

• Warning light illuminated on the instrument panel (typically a hydraulic oil temperature indicator)
• Erratic or frozen temperature gauge readings on the monitor display
• Intermittent code activation that appears and disappears, especially during warm-up cycles
• Potential machine derate or reduced hydraulic response if the ECM enters fail-safe mode
• No temperature warnings even when hydraulic oil is visibly hot (in cases of complete sensor failure)

Potential Causes

The most common technical causes for Code E-27 on used PC110-7 excavators include:

• Faulty hydraulic oil temperature sensor with internal resistance drift or complete failure
• Damaged or corroded wiring harness connections at the sensor plug (common wear point near the hydraulic tank)
• Chafed wiring where the sensor harness contacts metal edges or vibrates against structural components
• Poor ground connection causing voltage irregularities in the sensor circuit
• Corroded pins in the ECM connector affecting signal transmission
• Rare: ECM internal circuit failure affecting the temperature monitoring channel

How to Troubleshoot and Fix Code E-27

Step 1: Visual Inspection and Connection Check Begin by locating the hydraulic oil temperature sensor mounted on the hydraulic tank (typically on the right side of the PC110-7). Disconnect the sensor connector and inspect for corrosion, oil contamination, or bent pins. On used excavators, this connector frequently shows green corrosion or oil intrusion. Clean contacts with electrical contact cleaner and verify the connector locks securely.

Step 2: Sensor Resistance Testing Using a digital multimeter, measure the sensor's resistance across its terminals. At room temperature (20°C/68°F), resistance should typically read between 2,000-3,000 ohms (consult your service manual for exact specifications). If readings show infinite resistance (open circuit) or near-zero ohms (short circuit), the sensor has failed and requires replacement. For used machines, also heat the sensor gently with a heat gun while monitoring resistance—it should decrease smoothly as temperature rises.

Step 3: Wiring Harness Continuity Check Trace the sensor harness from the sensor to the ECM connector. Check for continuity between sensor terminals and corresponding ECM pins using wiring diagrams. Pay special attention to known rub points where the harness passes near the swing bearing and along the frame. On used PC110-7s, harness wear near mounting clamps is common. Verify ground circuit integrity separately, as poor grounds frequently cause intermittent codes.

Step 4: Voltage Supply Verification With ignition on and sensor disconnected, measure supply voltage at the sensor connector (typically 5V reference from ECM). If voltage is absent or incorrect, trace back toward the ECM checking for breaks or shorts. Replace damaged harness sections with proper gauge wire and ensure proper routing away from heat sources and moving components.

Step 5: Code Clearing and Verification After repairs, clear the fault code using Komatsu diagnostic software (KOMTRAX or compatible scan tool) and operate the machine through a complete heat cycle. Monitor live data to confirm the temperature sensor provides realistic readings that change appropriately with operating conditions.

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Disclaimer: This guide provides general troubleshooting procedures for Komatsu PC110-7 fault code E-27. Always consult the official Komatsu service manual for your specific machine serial number. If you lack proper diagnostic tools or experience with hydraulic systems and electrical diagnostics, consult a certified Komatsu technician to avoid misdiagnosis or safety hazards.