What is Komatsu PC220-8 Fault Code S-6?

Komatsu PC220-8 Fault Code S-6 indicates a malfunction in the hydraulic oil temperature sensor circuit. This diagnostic trouble code (DTC) is triggered when the Engine Control Module (ECM) detects an abnormal voltage signal from the hydraulic oil temperature sensor, typically reading either excessively high (open circuit) or abnormally low (short circuit) values outside the manufacturer's specified range.

This code is critical for the PC220-8's performance because the hydraulic system relies on accurate temperature monitoring to prevent overheating and maintain optimal viscosity. When the ECM cannot verify proper hydraulic oil temperature, it may implement protective measures including reduced hydraulic flow or power derate to prevent catastrophic damage to pumps, motors, and cylinder seals.

Common Symptoms

When Fault Code S-6 is active on your Komatsu PC220-8, operators typically experience:

• Hydraulic oil temperature warning light illuminated on the monitor panel
• Reduced hydraulic performance including slower cycle times and diminished digging force
• Engine derate mode activating prematurely, limiting RPM and power output
• Monitor display showing erratic or frozen temperature readings (often -40°C or 300°C+)
• Intermittent warning beeper activation during operation, especially under load

Potential Causes

For used Komatsu PC220-8 excavators, the most common technical causes include:

• Hydraulic oil temperature sensor failure due to internal resistance drift or element degradation
• Wiring harness damage at known rub points near the hydraulic tank and along the boom base
• Corroded or loose connector pins at the sensor plug or ECM interface
• Damaged sensor threads causing poor thermal contact with hydraulic reservoir
• ECM internal fault affecting the sensor input circuit (less common)
• Aftermarket sensor incompatibility if previous repairs used non-OEM parts

How to Troubleshoot and Fix Code S-6

Step 1: Visual Inspection Begin with a thorough physical examination of the hydraulic oil temperature sensor located on the hydraulic tank. Check for oil leaks around the sensor threads, physical damage to the sensor body, and corrosion on the electrical connector. On used excavators, inspect the entire wiring harness from sensor to ECM for chafing, particularly where it passes near moving components or metal edges.

Step 2: Electrical Testing Disconnect the sensor connector and use a digital multimeter to measure sensor resistance. At ambient temperature (20°C), resistance should typically read 2,000-3,000 ohms (consult your service manual for exact specifications). Test harness continuity from the sensor connector to the ECM pins, checking for opens or shorts to ground. Measure voltage supply from the ECM—it should provide approximately 5 volts reference signal.

Step 3: Component Replacement and Verification If resistance values are out of specification or erratic, replace the hydraulic oil temperature sensor with a genuine Komatsu part (part number 7861-93-3320 or equivalent). Before installation, apply anti-seize compound to threads and ensure proper torque (typically 20-25 N⋅m). Clear the fault code using Komatsu diagnostic software (KOMTRAX or PC Service Tool) and monitor for code recurrence during a full thermal cycle. For used machines, consider replacing the sensor connector pigtail if pins show corrosion.

Disclaimer: This guide provides general troubleshooting information. Always consult the official Komatsu PC220-8 service manual and consider professional diagnostic services for complex electrical issues or when working with high-voltage systems.