What is Komatsu PC220-7 Fault Code E-27?

Komatsu PC220-7 fault code E-27 indicates a malfunction in the hydraulic oil temperature sensor circuit. This code is triggered when the engine control module (ECM) detects an abnormal voltage signal from the temperature sensor monitoring the hydraulic oil, typically indicating either an open circuit, short circuit, or sensor failure.

The hydraulic oil temperature sensor plays a critical role in protecting the PC220-7's hydraulic system by monitoring oil temperature and alerting the operator when temperatures exceed safe operating limits. When this sensor circuit fails, the ECM cannot accurately monitor hydraulic system health, potentially leading to overheating damage, reduced component lifespan, and costly repairs. For used excavators, this code often appears due to age-related wiring deterioration or connector corrosion rather than actual sensor failure.

Common Symptoms

• Hydraulic oil temperature warning light illuminated on the instrument panel (amber or red)
• Intermittent gauge readings showing erratic or frozen temperature displays
• ECM may activate derate mode limiting engine RPM to prevent potential hydraulic system damage
• Abnormal hydraulic operation including sluggish cylinder movement, especially during cold starts
• Diagnostic display showing E-27 code when accessed through the monitor panel

Potential Causes

The most common causes for code E-27 on used Komatsu PC220-7 excavators include:

• Damaged or corroded wiring harness particularly where the harness routes near the hydraulic tank and experiences vibration or heat exposure
• Failed hydraulic oil temperature sensor due to internal resistance drift or element failure (common after 5,000+ hours)
• Corroded or loose connector pins at the sensor plug connection point, especially on machines operating in wet or marine environments
• Broken or chafed wires at known rub points near the hydraulic tank mounting brackets
• ECM internal fault (rare, but possible in high-hour machines with previous electrical issues)
• Poor ground connection affecting sensor circuit reference voltage

How to Troubleshoot and Fix Code E-27

Step 1: Visual Inspection Begin with a thorough visual inspection of the hydraulic oil temperature sensor located on the hydraulic tank. Check the wiring harness for obvious damage, chafing, or oil contamination. On used excavators, pay special attention to where the harness passes near sharp edges or heat sources. Inspect the connector for corrosion, bent pins, or moisture intrusion—clean with electrical contact cleaner if needed.

Step 2: Sensor Resistance Testing Disconnect the sensor connector and use a digital multimeter to measure resistance across the sensor terminals. For the PC220-7, typical resistance values range from 200-400 ohms at 68°F (20°C), decreasing as temperature increases. Compare your readings against Komatsu specifications. If readings show infinite resistance (open circuit) or zero ohms (short circuit), replace the sensor.

Step 3: Circuit Voltage and Continuity Check With the sensor disconnected and ignition on, measure supply voltage at the harness connector—should read approximately 5 volts. Check continuity between the sensor harness and ECM pins using a wiring diagram. For used machines, perform a "wiggle test" while monitoring voltage to identify intermittent connection issues caused by harness wear.

Step 4: Ground Circuit Verification Verify the sensor ground circuit has less than 0.5 ohms resistance to chassis ground. Poor grounding is a frequent culprit in older excavators with corroded frame connections.

Step 5: Replace Components as Needed If testing confirms sensor failure, install a genuine Komatsu replacement sensor (part number specific to PC220-7). If wiring is damaged, repair using heat-shrink solder connections rather than crimp connectors to ensure long-term reliability in harsh environments. Clear codes using Komatsu diagnostic software or the monitor panel, then test operation.

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Disclaimer: This guide provides general diagnostic information for Komatsu PC220-7 fault code E-27. Always consult the official Komatsu service manual for your specific serial number and seek professional assistance from certified technicians for complex electrical diagnostics or if you're unfamiliar with high-voltage systems.