What is Komatsu PC120LC-6 Fault Code E222?

Fault Code E222 on the Komatsu PC120LC-6 indicates a malfunction in the hydraulic oil temperature sensor circuit. This diagnostic trouble code (DTC) is triggered when the Electronic Control Module (ECM) detects an abnormal voltage signal from the temperature sensor monitoring the hydraulic oil temperature in the main system.

The hydraulic oil temperature sensor is critical for the PC120LC-6's performance management system. It provides real-time data to the ECM, which uses this information to prevent overheating, adjust pump output, and protect hydraulic components from thermal damage. When this sensor circuit fails, the machine loses its ability to monitor and regulate hydraulic system temperature effectively, potentially leading to reduced efficiency or component damage if operation continues under extreme conditions.

Common Symptoms

When Code E222 is active on your PC120LC-6, you may experience:

• Warning light illuminated on the instrument panel, typically accompanied by an audible alarm
• Reduced hydraulic performance or slower cycle times as the ECM enters a protective derate mode
• Erratic temperature gauge readings showing unusually high, low, or fluctuating hydraulic oil temperatures
• Intermittent fault activation, especially during cold starts or after prolonged operation
• Machine may continue operating but with limited performance to prevent potential thermal damage

Potential Causes

The most common technical reasons for Code E222 on used PC120LC-6 excavators include:

• Faulty hydraulic oil temperature sensor due to internal element degradation or moisture intrusion
• Damaged or corroded wiring harness between the sensor and ECM, particularly at connector points near the hydraulic tank
• Poor electrical connections caused by vibration-loosened terminals or corrosion buildup on sensor connectors
• Shorted or open sensor circuit from wiring chafing against frame components or hydraulic lines
• ECM-related issues, though less common, including internal circuit board failures or software glitches
• Compromised sensor mounting, allowing oil leaks that contaminate electrical connections

How to Troubleshoot and Fix Code E222

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 and wiring harness for visible damage, corrosion, oil contamination, or loose connections. On used excavators, pay special attention to wire routing where the harness may rub against metal edges or hydraulic components.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor connector and measure resistance across the sensor terminals. Compare readings against Komatsu specifications (typically 200-400 ohms at 20°C, varying with temperature). Check for continuity between the sensor connector and ECM pins. Test for voltage supply (typically 5V reference) from the ECM at the sensor connector with ignition on.

Step 3: Signal Verification If resistance values are within specification, reconnect the sensor and use Komatsu diagnostic software (KOMTRAX or compatible diagnostic tool) to monitor live sensor data. Compare actual hydraulic oil temperature with sensor readings. An out-of-range voltage (below 0.5V or above 4.5V) typically indicates sensor failure.

Step 4: Harness and Ground Testing Inspect the entire wiring harness from sensor to ECM, checking for chafing points common on the PC120LC-6 near the swing bearing and along the undercarriage. Verify proper ground connection at both the sensor and ECM locations, as corrosion on ground points is a frequent issue in used machines.

Step 5: Component Replacement Replace the faulty component based on test results. When installing a new temperature sensor, apply dielectric grease to connector terminals to prevent future corrosion. If replacing wiring, ensure proper routing away from heat sources and sharp edges, securing with appropriate clamps.

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