What is Komatsu PC450-7 Fault Code E118?

Fault Code E118 on the Komatsu PC450-7 excavator indicates a malfunction in the hydraulic oil temperature sensor circuit, specifically detecting an abnormally high voltage signal or open circuit condition in the temperature sensor wiring. This code is registered by the machine's Electronic Control Module (ECM) when the hydraulic oil temperature sensor fails to provide accurate readings within the expected voltage range (typically 0.5-4.5V).

This fault is critical for the PC450-7 because the hydraulic system temperature directly affects viscosity, component wear, and overall machine protection. The ECM relies on accurate temperature data to prevent hydraulic system damage by engaging warning systems or implementing power derate modes when temperatures exceed safe operating limits. In used excavators, this sensor circuit is particularly vulnerable to age-related deterioration.

Common Symptoms

• Hydraulic oil temperature warning lamp illuminated continuously on the instrument panel
• Inaccurate or fixed temperature readings displayed (often showing maximum temperature or dashes)
• Engine power derate mode engaged, limiting machine performance even when hydraulic oil is at normal temperature
• Intermittent fault code appearance, especially during machine vibration or movement
• Abnormal cooling fan cycling (running continuously or not engaging when needed)

Potential Causes

The most common technical causes for E118 on used PC450-7 excavators include:

• Damaged or corroded wiring harness connections at the hydraulic tank sensor mounting location (prone to moisture and debris contamination)
• Failed hydraulic oil temperature sensor (NTC thermistor) due to age-related internal breakdown or physical damage
• Open circuit in sensor wiring caused by harness chafing against frame components near the main hydraulic tank
• Poor ground connections at the sensor or ECM ground points (common in machines with 8,000+ operating hours)
• Water intrusion into sensor connectors causing high resistance or intermittent open circuits
• Corroded pins in the main wiring harness connector (particularly at bulkhead pass-throughs)

How to Troubleshoot and Fix Code E118

Step 1: Visual Inspection and Connector Check Begin by locating the hydraulic oil temperature sensor mounted on the hydraulic tank (typically on the right-hand side). Disconnect the sensor connector and inspect for corrosion, bent pins, or moisture contamination. Clean contacts with electrical contact cleaner and examine the wiring harness for visible damage, especially where it routes near sharp edges or moving components common in used excavators.

Step 2: Sensor Resistance Testing Using a digital multimeter, measure the resistance across the sensor terminals with the connector disconnected. At room temperature (20°C/68°F), resistance should typically read between 2,000-3,000 ohms. Compare readings against Komatsu specifications in the service manual. If resistance is infinite (open circuit) or zero (short circuit), replace the sensor.

Step 3: Circuit Voltage and Wiring Verification With the ignition key ON and sensor disconnected, check for reference voltage at the harness connector (should read approximately 5V). If voltage is absent, trace the wiring back toward the ECM checking for breaks or damaged insulation. On used machines, pay special attention to harness wear points near hydraulic lines and structural members.

Step 4: Ground Circuit Verification Verify continuity between the sensor ground wire and chassis ground using your multimeter (should read less than 1 ohm resistance). Clean and tighten all ECM ground connections, as oxidation over time commonly causes high resistance faults.

Step 5: Clear Code and Test After repairs, use Komatsu diagnostic software (KTMS or compatible scan tool) to clear the fault code. Operate the machine through a complete work cycle monitoring live data to confirm accurate temperature readings and verify the code does not return.

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Disclaimer: This guide provides general troubleshooting information for the Komatsu PC450-7. Always consult the official Komatsu service manual for your specific machine serial number and consider engaging a certified Komatsu technician for complex electrical diagnostics, especially on used equipment where multiple underlying issues may exist.