Komatsu PC55MR-2 Fault Code E-6: Complete Diagnostic Guide

What is Komatsu PC55MR-2 Fault Code E-6?

Fault Code E-6 on the Komatsu PC55MR-2 indicates a malfunction in the hydraulic oil temperature sensor circuit. This code triggers when the Engine Control Module (ECM) detects an abnormal voltage signal from the temperature sensor monitoring the hydraulic oil temperature in the main hydraulic circuit.

The hydraulic oil temperature sensor plays a critical role in protecting your PC55MR-2's hydraulic system from overheating damage. When the sensor circuit malfunctions, the ECM cannot accurately monitor oil temperature, potentially leading to component damage from overheating or unnecessary machine shutdowns. For compact excavators like the PC55MR-2 operating in confined spaces, maintaining proper hydraulic temperature is essential for consistent performance and preventing costly repairs.

Common Symptoms

When Code E-6 is active, operators typically experience:

• Warning light illumination on the instrument panel (often a hydraulic system warning indicator)
• Intermittent loss of hydraulic power or sluggish hydraulic response during operation
• Erratic temperature gauge readings or temperature display showing dashes/error symbols
• Automatic machine derate or shutdown in severe cases, especially if the ECM enters failsafe mode
• Cooling fan running continuously as the ECM assumes worst-case temperature conditions

Potential Causes

The most common technical failures triggering E-6 on used PC55MR-2 excavators include:

• Failed hydraulic oil temperature sensor due to internal element degradation (common after 5,000+ operating hours)
• Damaged or corroded wiring harness at the sensor connector, particularly where the harness routes near the hydraulic tank
• Broken or chafed sensor wires caused by contact with rotating components or hydraulic hoses
• Corroded connector terminals from moisture intrusion in the hydraulic tank area
• Poor ground connection at the sensor mounting point due to rust or paint buildup
• ECM internal fault (rare, but possible in machines with electrical system history)

How to Troubleshoot and Fix Code E-6

Step 1: Visual Inspection Begin by inspecting the hydraulic oil temperature sensor located on the hydraulic oil tank. Check the wiring harness for obvious damage, chafing, or oil contamination. On used excavators, pay special attention to areas where the harness may contact the tank or nearby hydraulic lines—this is a common wear point on the PC55MR-2.

Step 2: Connector and Ground Check Disconnect the sensor connector and inspect terminals for corrosion, bent pins, or moisture. Clean with electrical contact cleaner if needed. Verify the ground connection at the sensor mounting bracket by removing surface rust or paint to ensure metal-to-metal contact.

Step 3: Sensor Resistance Test Using a digital multimeter, measure the sensor's resistance. At room temperature (68°F/20°C), resistance should typically read between 2,000-3,000 ohms (consult your service manual for exact specifications). If readings are infinite (open circuit) or near zero (short circuit), replace the sensor.

Step 4: Wiring Harness Continuity Test With the sensor disconnected, check continuity between the sensor connector and the ECM connector. Also check for shorts to ground. Resistance should be less than 5 ohms for continuity, and infinite for insulation resistance.

Step 5: Clear Code and Test After repairs, clear the fault code using Komatsu diagnostic software (KOMTRAX or compatible scan tool) and operate the machine through a normal work cycle. Monitor for code recurrence and verify temperature gauge operation.

For used excavators, replacing the sensor often resolves E-6, but always verify wiring integrity first to avoid unnecessary parts replacement.

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Disclaimer: This guide provides general troubleshooting information. Always consult the official Komatsu PC55MR-2 service manual and consider professional diagnostic assistance for complex electrical issues or if you lack proper diagnostic equipment.