Komatsu PC850SE-8R Fault Code E-23: Complete Diagnostic Guide

What is Komatsu PC850SE-8R Fault Code E-23?

Fault Code E-23 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 temperature values from the hydraulic oil temperature sensor located in the main hydraulic tank.

For the PC850SE-8R, this code is critical because hydraulic oil temperature directly affects system viscosity, component protection, and overall machine performance. The ECM uses this data to regulate cooling fan speed, prevent overheating damage, and optimize hydraulic efficiency. Ignoring this fault can lead to accelerated wear on hydraulic pumps, motors, and cylinders.

Common Symptoms

When Code E-23 is active, operators typically experience:

• Warning light illuminated on the monitor panel with "E-23" displayed
• Cooling fan running continuously at high speed regardless of actual oil temperature
• Reduced hydraulic response or sluggish operation during cold starts
• Machine derate or automatic shutdown in severe cases to protect hydraulic components
• Inaccurate hydraulic oil temperature readings on the display (showing extremely high or low values)

Potential Causes

The most common technical causes for E-23 on used PC850SE-8R excavators include:

• Hydraulic oil temperature sensor failure due to age, contamination, or internal element degradation
• Damaged or corroded wiring harness connections at the sensor plug (common wear point near hydraulic tank)
• Chafed wiring where the harness routes along the frame or crosses moving components
• Contaminated hydraulic oil causing sensor element fouling
• ECM internal fault (rare, but possible in high-hour machines)
• Poor ground connections at sensor mounting points due to rust or paint buildup

How to Troubleshoot and Fix Code E-23

Step 1: Visual Inspection Begin by locating the hydraulic oil temperature sensor on the main hydraulic tank. Inspect the sensor connector for corrosion, oil contamination, bent pins, or moisture intrusion. On used excavators, check the wiring harness routing for signs of rubbing, especially where it passes near the swing bearing or along frame rails.

Step 2: Electrical Testing Disconnect the sensor and use a multimeter to check resistance across the sensor terminals. Compare readings against Komatsu specifications (typically 200-400 ohms at 20°C, varying with temperature). Check for continuity in the wiring harness from sensor to ECM connector. Verify ground circuit integrity with less than 5 ohms resistance.

Step 3: Diagnostic Software Analysis Connect Komatsu diagnostic software (KOMTRAX Plus or equivalent) to read live sensor data. Compare actual hydraulic oil temperature (use infrared thermometer) against displayed values. A variance greater than 10°C indicates sensor failure.

Step 4: Component Replacement If testing confirms sensor failure, replace with genuine Komatsu parts. Clean mounting threads and apply anti-seize compound. For used machines, always replace the connector pigtail if corrosion is present—this prevents recurring faults.

Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu service manual for your specific serial number and seek qualified technician assistance for complex electrical diagnostics or ECM programming.