What is Komatsu PC110-7 Fault Code H-21?

Komatsu PC110-7 Fault Code H-21 indicates a hydraulic pump pressure sensor circuit malfunction or abnormal signal detection in the main hydraulic system. This diagnostic trouble code (DTC) is triggered when the Electronic Control Module (ECM) receives voltage readings outside the specified range from the main pump pressure sensor, typically between 0.5-4.5 volts during normal operation.

This code is critical for the PC110-7 because the hydraulic pump pressure sensor directly monitors system pressure that controls all excavator functions—boom, arm, bucket, and swing operations. When the ECM cannot accurately read hydraulic pressure, it may limit machine performance to prevent catastrophic pump damage or enter a protective derate mode. On used excavators, this sensor and its wiring harness are particularly vulnerable to vibration fatigue and environmental contamination after thousands of operating hours.

Common Symptoms

• Hydraulic system warning light illuminated on the instrument cluster
• Noticeable loss of hydraulic power across all functions or intermittent sluggish response
• Machine entering reduced power mode where attachment speeds are significantly slower
• Erratic hydraulic operation where boom or arm movements become unpredictable
• Error code H-21 stored in the ECM memory accessible through diagnostic software

Potential Causes

The most common technical causes for H-21 on used PC110-7 excavators include:

• Faulty hydraulic pump pressure sensor due to internal component degradation (typical failure point after 6,000+ hours)
• Damaged or corroded wiring harness connecting the sensor to the ECM, especially at connector pin locations
• Harness chafing at known rub points near the main pump mounting area where vibration causes insulation wear
• Contaminated sensor connector with hydraulic oil, dirt, or moisture causing resistance issues
• ECM internal fault (less common) affecting the sensor input circuit
• Loose or broken ground connections in the hydraulic system electrical circuit

How to Troubleshoot and Fix Code H-21

Step 1: Visual Inspection Begin with a thorough inspection of the pressure sensor located on the main hydraulic pump body. Check for physical damage, oil contamination on the connector, or loose mounting. On used machines, inspect the wiring harness from sensor to ECM for visible damage, especially where it routes near moving components or hot surfaces.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor connector and measure resistance across sensor terminals (specification typically 200-400 ohms at 20°C). Check supply voltage at the harness connector—should read approximately 5 volts with ignition on. Test continuity through the harness to the ECM and verify ground circuit integrity (less than 1 ohm resistance).

Step 3: Connector and Harness Inspection For used excavators, carefully clean all connector pins with electrical contact cleaner and inspect for corrosion or bent pins. Check harness for internal wire breaks by gently flexing the wire while monitoring continuity. Pay special attention to areas where the harness passes through grommets or near the pump mounting brackets—common failure points.

Step 4: Component Replacement If sensor readings are out of specification or harness shows damage, replace the faulty component using genuine Komatsu parts to ensure proper ECM communication. After replacement, clear the code using Komatsu diagnostic software (KOMTRAX or compatible scan tool) and perform a function test under load.

Disclaimer: This guide provides general troubleshooting information. Always consult the official Komatsu PC110-7 service manual and consider professional diagnosis for complex electrical issues. Improper repairs may lead to further system damage or safety hazards.