Komatsu PC850-8R Fault Code E-26: Complete Diagnostic Guide

What is Komatsu PC850-8R Fault Code E-26?

Fault Code E-26 indicates a malfunction in the hydraulic oil temperature sensor circuit or an abnormal hydraulic oil temperature reading. This code is triggered when the Electronic Control Module (ECM) detects either an open circuit, short circuit, or out-of-range signal from the hydraulic oil temperature sensor located in the main hydraulic tank.

For the PC850-8R, this sensor is critical because it monitors hydraulic fluid temperature to prevent system damage and optimize performance. The ECM uses this data to adjust pump output, activate cooling fans, and protect hydraulic components from thermal degradation. When this sensor fails, the machine may enter a protective derate mode, significantly impacting productivity on job sites.

Common Symptoms

When Code E-26 is active, operators typically experience:

• Warning light illumination on the monitor panel with a hydraulic temperature alert
• Reduced hydraulic power or sluggish boom/arm/bucket response due to ECM derate
• Cooling fan running continuously at high speed, even during cold starts
• Erratic temperature gauge readings showing unrealistic values (extremely high or low)
• Machine shutdown in severe cases when the ECM cannot verify safe operating temperatures

Potential Causes

The most common technical causes for E-26 on used PC850-8R excavators include:

• Sensor failure due to age, thermal cycling, or internal element degradation
• Wiring harness damage at known rub points near the hydraulic tank mounting brackets
• Corroded or loose connector pins at the sensor plug (common in machines operating in wet/muddy conditions)
• Damaged sensor threads causing poor thermal contact with hydraulic fluid
• ECM internal fault (rare, but possible in high-hour machines)
• Hydraulic oil contamination causing sensor element coating or failure

How to Troubleshoot and Fix Code E-26

Step 1: Visual Inspection Begin by inspecting the hydraulic oil temperature sensor located on the main hydraulic tank. Check for physical damage, oil leaks around the sensor body, and examine the wiring harness for abrasion, cuts, or heat damage. On used excavators, pay special attention to harness routing near moving components and sharp edges.

Step 2: Connector and Resistance Testing Disconnect the sensor connector and inspect for corrosion, bent pins, or moisture intrusion. Using a digital multimeter, measure sensor resistance across the terminals. At 20°C (68°F), resistance should typically read between 2,000-3,000 ohms (consult your service manual for exact specifications). Compare readings at different temperatures to verify proper sensor response.

Step 3: Circuit Voltage Check With the sensor disconnected and ignition on, measure supply voltage at the harness connector. You should see approximately 5 volts from the ECM. If voltage is absent or incorrect, trace the harness back to the ECM, checking for breaks or shorts to ground.

Step 4: Sensor Replacement and Verification If testing confirms sensor failure, replace with a genuine Komatsu temperature sensor (Part #: verify with dealer). Apply anti-seize compound to threads and torque to specification. Clear codes using Komatsu diagnostic software (KOMTRAX) or a compatible scan tool, then monitor for code recurrence during operation.

Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu service manual for your specific machine serial number. Complex electrical issues should be diagnosed by certified Komatsu technicians with proper diagnostic equipment.