What is Komatsu PC210-8 Fault Code H-27?

Fault Code H-27 on the Komatsu PC210-8 excavator indicates a hydraulic oil temperature sensor circuit malfunction or abnormal high-temperature reading in the hydraulic system. This diagnostic trouble code (DTC) is triggered when the machine's 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 thresholds (typically above 110-120°C or 230-248°F).

This code is critical for the PC210-8 because sustained high hydraulic oil temperatures can rapidly degrade seals, accelerate component wear, reduce hydraulic efficiency, and potentially cause catastrophic system failures. The machine may enter a derated mode to protect hydraulic pumps, motors, and cylinders from thermal damage.

Common Symptoms

When Code H-27 is active on your Komatsu PC210-8, operators typically experience:

• Hydraulic oil temperature warning light illuminated on the monitor panel (amber or red depending on severity)
• Reduced machine performance with sluggish hydraulic response or limited swing/boom speed
• Automatic engine derate where RPM is limited to protect the hydraulic system
• Audible alarm from the cab monitoring system
• Overheating hydraulic oil with possible oil degradation smell or visible discoloration in sight glass

Potential Causes

The most common technical causes for H-27 on used PC210-8 excavators include:

• Failed or degraded hydraulic oil temperature sensor (common failure point after 5,000+ hours)
• Corroded or damaged wiring harness connections at the sensor plug (typically located near the hydraulic oil cooler)
• Blocked or restricted hydraulic oil cooler reducing heat dissipation capacity
• Low hydraulic oil level causing excessive friction and temperature buildup
• Contaminated or degraded hydraulic oil with reduced thermal properties
• Faulty ECM misreading sensor signals (less common but possible in high-hour machines)
• Actual hydraulic system overheating due to pump wear, relief valve issues, or excessive system pressure

How to Troubleshoot and Fix Code H-27

Step 1: Visual Inspection and Basic Checks Start by checking the hydraulic oil level in the reservoir when the machine is cold. Inspect the hydraulic oil cooler for external blockages (dirt, debris, bent fins). Examine the wiring harness running from the temperature sensor to the ECM for abrasion points, particularly where it routes near moving components or sharp edges—a common issue on used excavators.

Step 2: Test the Hydraulic Oil Temperature Sensor Locate the temperature sensor (typically mounted on the hydraulic tank or return line). Disconnect the sensor connector and use a digital multimeter to measure resistance. For the PC210-8, the sensor should read approximately 2,000-3,000 ohms at 20°C (68°F) depending on the specific sensor type. Compare readings against Komatsu specifications. Check for corrosion on connector pins—clean with electrical contact cleaner if necessary.

Step 3: Verify Wiring and ECM Communication With the sensor disconnected, measure voltage at the harness connector from the ECM side. You should see approximately 5 volts reference voltage. If voltage is absent or incorrect, trace the wiring for breaks or shorts. Use Komatsu diagnostic software (KOMTRAX Plus or compatible scan tool) to monitor live sensor data and confirm the ECM is receiving proper signals.

Step 4: Address Root Cause Issues If the sensor and wiring test normally, investigate actual hydraulic overheating. Flush and replace hydraulic oil if contaminated (especially important on used machines with unknown service history). Clean or replace the hydraulic oil cooler if restricted. Check hydraulic pump efficiency and system pressures to identify worn components causing excessive heat generation.

Disclaimer: This guide provides general troubleshooting information for experienced technicians. Always consult the official Komatsu PC210-8 service manual and follow proper safety procedures. For complex electrical diagnostics or major hydraulic repairs, consult a certified Komatsu technician or authorized service center.