What is Komatsu PC220-10 Fault Code H-31?

Komatsu PC220-10 fault code H-31 indicates a malfunction in the hydraulic oil temperature sensor circuit. This code is triggered when the engine control module (ECM) detects an abnormal voltage signal from the hydraulic oil temperature sensor, typically reading outside the normal operating range of 0.5-4.5 volts.

The hydraulic oil temperature sensor plays a critical role in the PC220-10's monitoring system by continuously measuring the temperature of the hydraulic fluid flowing through the system. When temperatures exceed safe operating limits (typically above 80-90°C), the ECM uses this data to protect vital hydraulic components from heat-related damage. For used excavators, this sensor's accuracy becomes increasingly important as aged hydraulic systems are more susceptible to overheating and component wear.

Common Symptoms

When fault code H-31 is active on your Komatsu PC220-10, you may experience:

• Hydraulic temperature warning light illuminated on the instrument cluster (yellow or red depending on severity)
• Engine derate mode activation, limiting RPM and reducing machine performance to prevent damage
• Inaccurate or erratic hydraulic oil temperature readings on the monitor display
• Automatic shutdown of the machine if the ECM cannot verify safe operating temperatures
• Intermittent loss of hydraulic power or sluggish attachment response during operation

Potential Causes

The most common technical reasons for H-31 code activation include:

• Failed hydraulic oil temperature sensor due to internal element degradation (common in excavators with 5,000+ hours)
• Damaged or corroded wiring harness connections at the sensor plug, especially at known rub points near the hydraulic tank
• Open circuit or short to ground in the sensor wiring, frequently caused by harness chafing against frame components
• Corroded sensor pins or moisture intrusion into the connector body, typical in machines exposed to wet environments
• ECM internal fault (rare) preventing proper voltage signal interpretation
• Aftermarket sensor installation with incorrect resistance specifications

How to Troubleshoot and Fix Code H-31

Step 1: Visual Inspection Begin by locating the hydraulic oil temperature sensor on the hydraulic tank (typically on the return line side). Inspect the sensor body for physical damage, oil leaks, or signs of overheating. Check the wiring harness from sensor to ECM for visible wear, cuts, or areas where the harness contacts metal surfaces—common failure points on used PC220-10 excavators.

Step 2: Electrical Testing Disconnect the sensor connector and use a digital multimeter to measure sensor resistance. At room temperature (20°C), the sensor should read approximately 2,000-3,000 ohms (consult your service manual for exact specifications). Check for voltage supply at the harness connector with ignition on—you should see approximately 5 volts reference voltage from the ECM.

Step 3: Harness Continuity Check With the sensor disconnected, test continuity between the sensor connector pins and the ECM harness connector. Any reading above 5 ohms indicates excessive resistance from corrosion or damaged wiring. Inspect connectors for green corrosion (typical in older machines) and clean with electrical contact cleaner.

Step 4: Sensor Replacement and Verification If testing confirms sensor failure, replace with a genuine Komatsu hydraulic temperature sensor (part number specific to PC220-10). Aftermarket sensors often have incorrect resistance curves causing false codes. Apply dielectric grease to connector pins before reassembly to prevent future corrosion. Clear codes using Komatsu diagnostic software (KOMTRAX) or compatible diagnostic tool, then monitor for code recurrence during a 30-minute operation cycle.

Disclaimer: This guide provides general troubleshooting information for experienced technicians. Hydraulic systems operate under high pressure and temperature. Always consult the official Komatsu PC220-10 service manual and consider professional diagnostic assistance for complex electrical issues or if you're unfamiliar with hydraulic system safety procedures.