What is Komatsu PC210LC-8 Fault Code H-21?

Fault Code H-21 on the Komatsu PC210LC-8 indicates a malfunction in the hydraulic pump discharge pressure sensor circuit. This diagnostic trouble code (DTC) is triggered when the Engine Control Module (ECM) detects abnormal voltage readings or signal interruptions from the pressure sensor monitoring the main hydraulic pump's output pressure.

The hydraulic pump discharge pressure sensor plays a critical role in the PC210LC-8's performance optimization system. It provides real-time feedback to the ECM, allowing the controller to adjust pump flow, regulate engine load, and maintain optimal fuel efficiency. When this sensor circuit fails, the excavator loses its ability to properly modulate hydraulic power delivery, potentially causing poor machine response, reduced productivity, and increased fuel consumption. For used excavators, this code often emerges due to age-related component degradation or electrical connection deterioration.

Common Symptoms

When Code H-21 becomes active on your Komatsu PC210LC-8, operators typically experience:

• Warning light illumination on the instrument panel with possible audible alarm
• Reduced hydraulic performance across all functions (boom, arm, bucket, and swing operations)
• Engine derating or limitation of maximum RPM to protect the hydraulic system
• Erratic hydraulic response where functions may feel sluggish or inconsistent
• Increased fuel consumption as the ECM cannot optimize pump-to-engine coordination

Potential Causes

The most common technical causes of H-21 on used PC210LC-8 excavators include:

• Faulty hydraulic pump discharge pressure sensor due to internal component failure or contamination exposure
• Damaged or corroded wiring harness connections between the sensor and ECM, particularly at connector pins
• Worn or chafed sensor harness where wiring rubs against frame components or hydraulic lines (common failure point near the pump mounting area)
• Contaminated electrical connectors from hydraulic fluid leakage or moisture intrusion in the engine compartment
• ECM internal circuit failure affecting the sensor signal processing pathway (less common)
• Poor ground connections in the sensor circuit causing voltage reference issues

How to Troubleshoot and Fix Code H-21

Step 1: Visual Inspection and Connection Verification Begin by thoroughly inspecting the hydraulic pump discharge pressure sensor located on the main pump assembly. Check for physical damage, hydraulic oil contamination on the connector, or obvious harness wear. Disconnect the sensor connector and examine both male and female pins for corrosion, bent terminals, or hydraulic fluid intrusion—extremely common on used excavators operating in harsh environments.

Step 2: Electrical Circuit Testing Using a digital multimeter, measure the sensor supply voltage with the key in the ON position (should typically read 5 volts). Check sensor signal wire continuity from the sensor connector back to the ECM connector. Measure ground circuit resistance, which should be less than 5 ohms. For used machines, pay special attention to harness routing—check for wire abrasion points where the harness contacts the pump housing or passes through frame brackets.

Step 3: Sensor and Component Replacement If voltage supply and ground circuits test correctly, measure the sensor output signal while comparing readings to Komatsu specifications (typically 0.5-4.5 volts depending on pressure). A static reading or out-of-range voltage indicates sensor failure. Replace the pressure sensor with a genuine Komatsu part, apply dielectric grease to connector pins, and secure all harness routing with new zip ties to prevent future chafing. Connect Komatsu diagnostic software (KOMTRAX or PC-based diagnostics) to verify code clearing and monitor live sensor data during test operation.

---

Disclaimer: This guide provides general troubleshooting information. Always consult the official Komatsu service manual for your specific machine serial number and seek qualified professional assistance for complex repairs or safety-critical systems.