Komatsu PC400LC-8 Fault Code DHS4MA: Complete Diagnostic Guide

What is Komatsu PC400LC-8 Fault Code DHS4MA?

Fault Code DHS4MA indicates a malfunction in the hydraulic system's pressure sensor circuit, specifically related to the main pump delivery pressure monitoring system. This code is triggered when the Engine Control Module (ECM) detects an abnormal voltage signal or communication error from the hydraulic pressure sensor that monitors the main pump's output pressure.

In the Komatsu PC400LC-8, this sensor plays a critical role in the machine's load-sensing hydraulic system. The ECM uses pressure data to optimize engine performance, prevent overload conditions, and ensure efficient fuel consumption. When this code activates, the machine may enter a protective derate mode to prevent potential damage to hydraulic components or the engine itself.

Common Symptoms

When DHS4MA is active on your PC400LC-8, operators typically experience:

• Hydraulic system derate with noticeably reduced boom, arm, or bucket speed
• Illuminated warning lamp on the monitor panel with fault code display
• Engine power limitation preventing the machine from reaching full RPM under load
• Intermittent loss of hydraulic responsiveness, especially during combined functions
• Audible alarm accompanied by the visual warning on the multi-function display

Potential Causes

The most common technical reasons for DHS4MA in used PC400LC-8 excavators include:

• Hydraulic pressure sensor failure due to internal component degradation or contamination exposure
• Damaged or corroded wiring harness connections at the sensor connector (common wear point near the main pump)
• Voltage supply issues from the ECM to the sensor circuit (typically 5V reference voltage)
• Contaminated hydraulic oil causing sensor membrane damage or erratic readings
• ECM internal fault affecting the pressure monitoring circuit (less common)
• Harness chafing at known rub points along the right-side frame rail near hydraulic tank

How to Troubleshoot and Fix Code DHS4MA

Step 1: Initial Inspection Using Komatsu diagnostic software (KOMTRAX Plus) or a compatible scan tool, record all active and pending codes. Check the sensor's live data stream to determine if pressure readings are erratic, stuck at zero, or showing maximum values.

Step 2: Physical and Electrical Checks Locate the main pump pressure sensor on the hydraulic pump assembly. Inspect the wiring harness for visible damage, oil contamination, or connector corrosion—critical on used machines with 5,000+ hours. Using a digital multimeter, verify the 5V reference voltage at the sensor connector with the key on, engine off.

Step 3: Sensor and Circuit Testing Measure sensor resistance (typically 200-400 ohms depending on temperature) and check for proper ground continuity. On used excavators, inspect connector pins for fretting corrosion caused by vibration. If voltage and resistance are within specifications, replace the pressure sensor and clear codes before condemning the ECM.

Disclaimer: This guide provides general troubleshooting information. Always consult the official Komatsu service manual for your specific machine serial number and consider professional diagnostic assistance for complex electrical issues.