Komatsu PC750SE-7 Fault Code H-13: Complete Diagnostic Guide

What is Komatsu PC750SE-7 Fault Code H-13?

Fault Code H-13 indicates a hydraulic oil temperature sensor circuit malfunction in the Komatsu PC750SE-7 excavator. This code is triggered when the Electronic 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 is critical for the PC750SE-7's performance management system. It monitors the temperature of hydraulic fluid flowing through the main circuit, allowing the ECM to adjust pump output, activate cooling fans, and prevent overheating damage to expensive hydraulic components. When this sensor fails or sends erratic signals, the machine cannot properly regulate hydraulic system temperatures, potentially leading to reduced efficiency, component wear, or catastrophic hydraulic system failure.

Common Symptoms

When Code H-13 is active, operators typically experience:

• Hydraulic oil temperature warning light illuminated on the monitor panel
• Cooling fan running continuously at high speed, regardless of actual oil temperature
• Reduced hydraulic performance or sluggish operation as the ECM enters protective derate mode
• Inaccurate temperature readings displayed on the monitor (showing extremely high or low values)
• Intermittent code activation during machine warm-up or under heavy load conditions

Potential Causes

The most common technical reasons for H-13 on used PC750SE-7 excavators include:

• Faulty hydraulic oil temperature sensor due to internal element degradation or contamination exposure
• Damaged wiring harness at known rub points near the hydraulic tank mounting brackets
• Corroded or loose connector pins at the sensor connection point (common in machines operating in wet/corrosive environments)
• ECM internal circuit failure affecting the sensor input channel (rare but possible in high-hour machines)
• Shorted or open circuit in the sensor signal wire between the sensor and ECM
• Contaminated hydraulic oil causing sensor element fouling

How to Troubleshoot and Fix Code H-13

Step 1: Visual Inspection Begin by locating the hydraulic oil temperature sensor (typically mounted on the hydraulic tank or main return line). Inspect the sensor connector for corrosion, bent pins, or oil contamination. On used excavators, check the wiring harness routing for signs of chafing against metal brackets or heat damage from nearby components.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure its resistance across the two terminals. At room temperature (20°C/68°F), resistance should typically read 2,000-3,000 ohms (consult your service manual for exact specifications). Test the harness continuity from the sensor connector back to the ECM, checking for opens or shorts to ground.

Step 3: Voltage Signal Check With the sensor connected and ignition on (engine off), backprobe the signal wire at the sensor connector. You should read approximately 5 volts reference voltage from the ECM. Start the engine and monitor voltage as the system warms—it should gradually decrease from ~3.5V (cold) to ~1.5V (operating temperature).

Step 4: Component Replacement If testing reveals a faulty sensor, replace it with a genuine Komatsu part or high-quality OEM equivalent. Before installation, apply dielectric grease to connector pins to prevent future corrosion—critical for used machines. Clear the code using Komatsu diagnostic software (KOMTRAX) or a compatible scan tool, then operate the machine through a complete heat cycle to verify the repair.

Disclaimer: This guide provides general diagnostic procedures. Always consult the official Komatsu PC750SE-7 service manual and consider professional assistance for complex electrical diagnostics or if you're unfamiliar with high-voltage systems.