What is Komatsu PC210-10 Fault Code H-31?

Fault Code H-31 on the Komatsu PC210-10 indicates a hydraulic oil temperature sensor circuit malfunction or abnormally high hydraulic oil temperature. This code is triggered when the Engine Control Module (ECM) detects either an out-of-range voltage signal from the hydraulic oil temperature sensor or confirms that operating temperatures have exceeded safe thresholds (typically above 110°C/230°F).

This code is critical for the PC210-10 because sustained high hydraulic oil temperatures degrade fluid viscosity, accelerate seal wear, and can cause catastrophic pump or motor failures. The Komatsu monitoring system uses this sensor to protect expensive hydraulic components and prevent thermal damage to precision-machined parts.

Common Symptoms

When Code H-31 is active, operators typically experience:

• Hydraulic system warning light illuminated on the monitor panel, often accompanied by audible alarm
• Reduced hydraulic response or sluggish boom/arm movements as the system enters protective derate mode
• Visible temperature gauge showing red zone readings on the multi-function display
• Automatic engine rpm limitation to reduce hydraulic system load
• Hot hydraulic oil smell or visible heat shimmer from the hydraulic tank area

Potential Causes

The most common technical reasons for H-31 on used PC210-10 excavators include:

• Faulty hydraulic oil temperature sensor with internal resistance drift (common after 6,000+ operating hours)
• Damaged wiring harness between sensor and ECM, particularly at flex points near the hydraulic tank mounting bracket
• Corroded or loose electrical connectors at the sensor plug, allowing moisture intrusion
• Genuine high hydraulic oil temperature caused by plugged oil cooler fins, failed cooling fan, or low coolant levels
• Inadequate hydraulic oil level or use of incorrect viscosity oil for operating conditions
• Worn hydraulic pumps generating excessive heat due to internal leakage in used machines

How to Troubleshoot and Fix Code H-31

Step 1: Visual Inspection Check the hydraulic oil level using the sight glass (machine level on flat ground). Inspect the oil cooler for debris blockage and examine the cooling fan operation. On used excavators, carefully inspect the sensor wiring harness for abrasion points where it contacts the tank frame—this is a known wear point on PC210 models.

Step 2: Sensor Testing Locate the hydraulic oil temperature sensor on the return line side of the hydraulic tank. Disconnect the two-pin connector and use a digital multimeter to measure resistance. At 20°C (68°F), resistance should read approximately 2,500 ohms (reference Komatsu specifications). Compare readings against a temperature-resistance chart. Check connector pins for corrosion or bent terminals.

Step 3: Circuit Verification With sensor disconnected, measure voltage supply at the harness connector—should read approximately 5 volts from the ECM. Check ground continuity to ECM using a multimeter (should show less than 1 ohm resistance). Inspect harness routing for chafing against sharp edges, especially common on machines with 5,000+ hours.

Step 4: Actual Temperature Confirmation Use an infrared thermometer to verify actual hydraulic oil temperature at the tank. If temperature exceeds 90°C during normal operation, address cooling system issues before sensor replacement. For used machines, consider flushing the oil cooler and replacing the thermostat valve.

Professional Disclaimer: While this guide provides technical troubleshooting steps, always consult Komatsu service documentation and consider professional diagnostic support for complex electrical issues. Improper repairs may void warranties or create safety hazards.