Komatsu PC200-8E0 Fault Code H-27: Complete Diagnostic Guide

What is Komatsu PC200-8E0 Fault Code H-27?

Fault Code H-27 indicates a hydraulic oil temperature sensor abnormality or malfunction in the Komatsu PC200-8E0 excavator. This code triggers when the Electronic Control Module (ECM) detects an irregular signal from the hydraulic oil temperature sensor, typically caused by open circuits, short circuits, or sensor degradation.

The hydraulic oil temperature sensor plays a critical role in monitoring operating temperatures within the hydraulic system. When temperatures exceed safe thresholds or the sensor fails to communicate properly, the ECM activates protective measures to prevent catastrophic hydraulic component damage. For used PC200-8E0 machines, this sensor is particularly vulnerable to heat cycling fatigue and electrical connector corrosion over thousands of operating hours.

Common Symptoms

When Code H-27 is active, operators typically experience:

• Warning lamp illumination on the monitor panel with "H-27" displayed
• Reduced machine performance or hydraulic system derate to protect components
• Erratic temperature readings on the dashboard display (showing abnormally high or low temps)
• Intermittent code activation, especially during warm-up or under heavy load conditions
• Sluggish hydraulic response as the ECM limits flow to prevent overheating

Potential Causes

The most common technical reasons for H-27 activation in used PC200-8E0 excavators include:

• Failed hydraulic oil temperature sensor due to heat exposure and age-related degradation
• Damaged or corroded wiring harness at the sensor connector (common rub point near the hydraulic tank)
• Poor electrical connections caused by vibration, moisture intrusion, or oxidized terminals
• Open or short circuit in the sensor signal wire between the sensor and ECM
• ECM internal fault (rare, but possible in high-hour machines with electrical system history)
• Aftermarket sensor incompatibility if previous repairs used non-OEM parts

How to Troubleshoot and Fix Code H-27

Step 1: Visual Inspection Begin with a thorough inspection of the hydraulic oil temperature sensor located on the hydraulic tank. Check the sensor connector for corrosion, bent pins, or oil contamination. On used excavators, inspect the wiring harness routing for chafing against metal edges—a notorious failure point on PC200-8E0 models near the swing bearing area.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure resistance across the sensor terminals. At room temperature (68°F/20°C), resistance should typically read between 2,000-3,000 ohms (consult Komatsu service manual for exact specifications). Test for continuity along the harness from the sensor connector to the ECM connector. Any reading showing infinite resistance (open circuit) or zero resistance (short circuit) indicates wiring faults.

Step 3: Sensor Voltage Check With the ignition on and sensor connected, back-probe the signal wire at the sensor connector. You should see approximately 5 volts reference voltage from the ECM. If voltage is absent, trace the circuit back to the ECM for breaks or check the ECM ground connections for corrosion.

Step 4: Component Replacement If testing confirms sensor failure, replace with genuine Komatsu parts (Part #7861-93-3320 or equivalent). For used machines, always replace the connector pigtail simultaneously to ensure reliable long-term operation. Clear codes using Komatsu diagnostic software (KOMTRAX) and verify repair through thermal cycle testing.

---

Disclaimer: This guide provides general troubleshooting information. Always consult the official Komatsu service manual for your specific machine serial number and consider professional diagnostic assistance for complex electrical issues or if you lack proper diagnostic equipment.