Caterpillar Fault Code 6586: Complete Diagnostic Guide

What is Caterpillar Fault Code 6586?

Fault Code 6586 indicates a Hydraulic Oil Temperature Sensor Circuit malfunction, specifically signaling that the Engine Control Module (ECM) has detected an abnormal voltage reading from the hydraulic oil temperature sensor. This code is part of Caterpillar's diagnostic trouble code (DTC) system and typically points to an open circuit, short circuit, or sensor degradation issue.

The hydraulic oil temperature sensor monitors the temperature of hydraulic fluid flowing through the excavator's hydraulic system. This data is critical because the ECM uses it to protect the machine from overheating damage, adjust hydraulic pump performance, and prevent component failure. On Caterpillar excavators, maintaining proper hydraulic oil temperature (typically 40-80°C operating range) is essential for optimal performance and longevity of pumps, valves, and cylinders.

Common Symptoms

When Code 6586 is active, operators may notice:

• Warning light or diagnostic lamp illuminated on the instrument cluster
• Inaccurate or erratic hydraulic oil temperature readings on the display (showing extremely high or low values)
• Reduced hydraulic performance or slower cycle times, especially if the ECM enters a protective derate mode
• Intermittent code activation, particularly when the machine vibrates or operates on rough terrain (suggesting a wiring issue)
• Engine power reduction in severe cases where the ECM limits performance to protect hydraulic components

Potential Causes

The most common technical causes for Code 6586 on used Caterpillar excavators include:

• Faulty hydraulic oil temperature sensor due to internal component degradation or contamination exposure
• Damaged or corroded wiring harness, especially at known rub points near the hydraulic tank or along the chassis frame
• Loose or corroded electrical connectors at the sensor or ECM connection points
• Open or short circuit in the sensor signal wire caused by pinching, abrasion, or rodent damage
• ECM internal fault (less common) affecting the sensor input circuit
• Poor ground connection affecting sensor voltage reference

How to Troubleshoot and Fix Code 6586

Step 1: Visual Inspection Begin by locating the hydraulic oil temperature sensor (typically mounted on the hydraulic tank). Inspect the sensor body for physical damage, oil leaks, or contamination. Check the electrical connector for corrosion, bent pins, or moisture intrusion—common on used machines. Disconnect and reconnect the connector to ensure proper seating.

Step 2: Wiring Harness Inspection Trace the sensor wiring harness from the sensor to the ECM, looking for wear points, abrasion, or pinch damage. Pay special attention to areas where the harness passes near metal edges, hydraulic lines, or moving components. On used excavators, harness friction and vibration-related damage are frequent culprits.

Step 3: Electrical Testing Using a digital multimeter, perform resistance and voltage checks. With the ignition off and sensor disconnected, measure sensor resistance—typically 2,000-3,000 ohms at room temperature for most Caterpillar sensors (consult your specific service manual). Check for 5-volt reference voltage at the sensor connector with the ignition on. Verify ground continuity (less than 1 ohm resistance) between the sensor ground pin and chassis ground.

Step 4: Diagnostic Software Scan Connect Caterpillar Electronic Technician (Cat ET) or compatible diagnostic software to read live sensor data. Compare the temperature reading from the sensor against actual hydraulic oil temperature (use an infrared thermometer for verification). If readings differ significantly or fluctuate erratically, the sensor likely requires replacement.

Step 5: Component Replacement If testing confirms sensor failure, replace the hydraulic oil temperature sensor with a genuine Caterpillar part. Ensure the new sensor is properly torqued and use dielectric grease on the electrical connector to prevent future corrosion. After installation, clear the fault code using diagnostic software and perform a test cycle to verify the repair.

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Disclaimer: This guide provides general diagnostic procedures for informational purposes. Always consult your Caterpillar service manual for model-specific procedures and specifications. If you lack the proper tools or experience, consult a certified Caterpillar technician to avoid equipment damage or safety hazards.