Komatsu PC850-8R Fault Code H-6: Complete Diagnostic Guide

What is Komatsu PC850-8R Fault Code H-6?

Fault Code H-6 on the Komatsu PC850-8R indicates a hydraulic oil temperature sensor malfunction or abnormal hydraulic system temperature reading. This code is triggered when the Electronic Control Module (ECM) detects either an out-of-range signal from the hydraulic oil temperature sensor or when hydraulic fluid temperatures exceed safe operating parameters.

This fault is critical for the PC850-8R because excessive hydraulic temperatures can cause rapid degradation of seals, accelerated fluid breakdown, and potential damage to hydraulic pumps and motors. The machine's monitoring system uses this sensor data to protect expensive hydraulic components and maintain optimal performance under heavy loads.

Common Symptoms

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

• Hydraulic temperature warning light illuminated on the monitor panel
• Reduced machine performance or automatic derate mode limiting hydraulic flow
• Audible warning alarm from the cab monitoring system
• Sluggish hydraulic response, particularly during high-demand operations
• Possible automatic shutdown if temperatures reach critical levels (safety protection mode)

Potential Causes

The most common technical causes for H-6 on used PC850-8R excavators include:

• Faulty hydraulic oil temperature sensor – sensor drift or internal failure common after 8,000+ operating hours
• Damaged or corroded wiring harness at sensor connector, especially near the hydraulic tank mounting point where vibration causes wire chafing
• Actual hydraulic overheating due to clogged oil cooler, low coolant flow, or failed cooling fan
• Poor electrical ground connection at the sensor mounting location due to corrosion or loose hardware
• ECM calibration issues or software glitches requiring parameter reset
• Contaminated hydraulic fluid causing genuine temperature spikes

How to Troubleshoot and Fix Code H-6

Step 1: Visual Inspection Begin by locating the hydraulic oil temperature sensor (typically mounted on the hydraulic tank). Inspect the wiring harness for visible damage, abrasion, or oil contamination. Check connector pins for corrosion or bent terminals – common on used machines operating in harsh environments.

Step 2: Electrical Testing Using a digital multimeter, measure sensor resistance. The PC850-8R temperature sensor should read approximately 2,000-3,000 ohms at ambient temperature (consult service manual for exact specifications). Test voltage supply at the connector (typically 5V reference from ECM). Check for proper ground continuity (less than 1 ohm resistance to chassis ground).

Step 3: Live Data Verification Connect Komatsu diagnostic software (KOMTRAX Plus or equivalent) to monitor real-time temperature readings. Compare sensor output against actual hydraulic oil temperature using an infrared thermometer. A variance greater than 10°C indicates sensor failure.

Step 4: Physical System Check If electrical tests pass, inspect the hydraulic oil cooler for blockage, verify cooling fan operation, and check hydraulic fluid level and condition. On used excavators, accumulated debris in cooler fins is extremely common.

Step 5: Component Replacement Replace the temperature sensor if readings are inconsistent. For used machines, always apply dielectric grease to new connectors and secure harnesses away from vibration points using proper routing clips.

---

Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu service manual for your specific machine serial number and consider professional technician assistance for complex repairs.