What is Komatsu PC120-6 Fault Code H-19?

Fault Code H-19 on the Komatsu PC120-6 indicates a hydraulic pump delivery pressure sensor malfunction or abnormal signal in the main hydraulic system. This code triggers when the Electronic Control Module (ECM) detects voltage readings from the pump pressure sensor that fall outside the expected range (typically 0.5-4.5V), or when there's a complete circuit failure.

This sensor monitors the main pump discharge pressure, which is critical for the PC120-6's load-sensing hydraulic system. When this code appears, the machine's ability to match hydraulic flow to demand is compromised, potentially causing inefficient operation, reduced digging force, or complete hydraulic system shutdown. For this mid-sized excavator model, maintaining accurate pressure readings ensures optimal fuel economy and prevents damage to expensive hydraulic components.

Common Symptoms

• Amber warning light illuminated on the instrument panel with possible audible alarm
• Reduced hydraulic power across all functions (boom, arm, bucket, swing)
• Sluggish or inconsistent response when operating multiple functions simultaneously
• Irregular engine RPM fluctuations under load due to improper pump compensation
• Machine may enter derate mode, limiting maximum working speed or preventing operation entirely

Potential Causes

The most common causes for H-19 on used PC120-6 excavators include:

Sensor failure: The pressure sensor itself degrades over time, particularly in machines with 5,000+ operating hours. Internal component wear or diaphragm fatigue causes erratic voltage output.

Wiring harness damage: On the PC120-6, the sensor harness runs along the main pump housing where it's exposed to hydraulic fluid spray and vibration. Look for chafed wires near mounting brackets or cracked insulation at the connector boot.

Connector corrosion: The 3-pin sensor connector accumulates moisture and hydraulic contamination, creating high resistance or intermittent connections.

ECM issues: Less common, but used machines may have ECM pin corrosion or internal circuit board failures affecting the sensor input channel.

Hydraulic system contamination: Metal particles or degraded hydraulic fluid can physically damage the sensor's sensing element.

How to Troubleshoot and Fix Code H-19

Step 1: Visual Inspection and Connector Check Locate the pump pressure sensor on the main hydraulic pump (right side of engine, mounted directly on pump body). Disconnect the 3-pin connector and inspect for bent pins, oil intrusion, or green corrosion. Clean with electrical contact cleaner and apply dielectric grease. For used excavators, carefully trace the entire harness checking for wear points where it contacts metal surfaces or zip-tie chafing.

Step 2: Sensor Resistance and Voltage Testing Using a digital multimeter, measure sensor resistance between signal and ground terminals (should read 200-400Ω at room temperature). With ignition ON but engine OFF, backprobe the signal wire (typically yellow or blue) – it should show approximately 0.5V at zero pressure. If readings are out of range or open circuit, replace the sensor.

Step 3: Circuit Verification and ECM Check If the sensor tests good, check harness continuity from sensor connector to ECM pins. Verify 5V reference voltage supply from ECM and confirm ground circuit has less than 0.1Ω resistance. Use Komatsu diagnostic software (KOMTRAX or PC service tool) to monitor live sensor data and compare against actual hydraulic pressure gauge readings. Discrepancies indicate ECM calibration issues.

Step 4: Hydraulic System Verification After electrical repairs, change hydraulic filters and check fluid condition. Metallic contamination suggests pump wear causing sensor damage.

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Disclaimer: This guide provides general troubleshooting information. Always consult the Komatsu PC120-6 service manual and consider professional diagnostic assistance for complex hydraulic-electrical issues, especially on used equipment with unknown maintenance history.