What is Komatsu PC100-6 Fault Code H-20?

Fault Code H-20 on the Komatsu PC100-6 indicates a hydraulic oil temperature sensor malfunction or abnormal high-temperature reading in the hydraulic system. This diagnostic trouble code (DTC) is triggered when the Engine Control Module (ECM) detects either an open circuit, short circuit, or irregular voltage signal from the hydraulic oil temperature sensor, or when actual oil temperatures exceed safe operational thresholds (typically above 110°C/230°F).

This code is critical for the PC100-6 because excessive hydraulic oil temperatures can cause rapid degradation of seals, hoses, and hydraulic fluid itself, leading to catastrophic pump failure or complete hydraulic system breakdown. The excavator's control system monitors this parameter continuously to protect expensive hydraulic components and maintain optimal viscosity for efficient operation.

Common Symptoms

• Warning light illuminated on the instrument panel (typically a red or amber hydraulic temperature indicator)
• Noticeable reduction in hydraulic response or sluggish boom/arm/bucket movements
• Audible alarm sounding intermittently or continuously when oil temperature rises
• Automatic power derate or engine speed limitation to protect the hydraulic system
• Visible smoke or burning smell from the hydraulic reservoir area in severe cases

Potential Causes

The most common causes for H-20 codes on used PC100-6 excavators include:

• Faulty hydraulic oil temperature sensor due to internal element degradation (common after 5,000+ operating hours)
• Damaged wiring harness near the hydraulic tank, especially where cables route over sharp edges or vibrate against the frame
• Corroded or loose connector pins at the sensor plug, allowing moisture intrusion (typical in machines operating in wet environments)
• Actual hydraulic oil overheating caused by clogged oil coolers, low coolant levels, or malfunctioning cooling fans
• ECM calibration issues or ground faults in older machines with previous electrical repairs

How to Troubleshoot and Fix Code H-20

Step 1: Visual Inspection Check the hydraulic oil temperature sensor located on the hydraulic tank for physical damage, oil leaks, or loose connections. Inspect the wiring harness from sensor to ECM for chafing, cuts, or signs of rodent damage—common failure points on used equipment.

Step 2: Electrical Testing Using a digital multimeter, measure sensor resistance. At room temperature (20°C), resistance should read approximately 2-3 kΩ (consult service manual for exact specifications). Check for continuity in the wiring and ensure ground circuit integrity. Voltage supply from ECM should measure 5V DC.

Step 3: Temperature Verification Use an infrared thermometer to verify actual hydraulic oil temperature against sensor readings via diagnostic software like Komatsu KOMTRAX or compatible scan tools. If physical temperature matches sensor output but remains high, inspect the hydraulic oil cooler for blockages and verify cooling fan operation.

Step 4: Component Replacement For used excavators, replace the sensor (Part #: 7861-93-1650 or equivalent) if resistance values are out of specification. Before installation, clean connector terminals with electrical contact cleaner and apply dielectric grease to prevent future corrosion.

Disclaimer: This guide provides general troubleshooting information. Always consult the official Komatsu service manual and consider professional diagnostic assistance for complex electrical issues or if safety concerns exist.