What is Komatsu PC400-7 Fault Code DHS4MA?

Fault code DHS4MA on the Komatsu PC400-7 indicates a hydraulic pump displacement sensor malfunction in the main hydraulic system. This code specifically relates to an abnormal signal detected from the pump displacement position sensor, which monitors the swash plate angle of the main hydraulic pumps.

The PC400-7's electronically controlled hydraulic system relies on this sensor to optimize pump output based on load demands. The Engine Control Module (ECM) and Pump Control Module work together to adjust hydraulic flow, making this sensor critical for fuel efficiency and preventing hydraulic system overload. When this code appears, the excavator typically enters a derate mode to protect the hydraulic components from damage due to incorrect displacement readings.

Common Symptoms

• Reduced hydraulic performance across all functions, with noticeably slower cycle times on bucket, boom, and swing operations
• Yellow hydraulic warning lamp illuminated on the instrument cluster, sometimes accompanied by the check engine light
• Inconsistent pump response where the machine alternates between normal and reduced power modes
• Abnormal whining or grinding noise from the main hydraulic pumps during operation
• Increased fuel consumption as the system cannot properly match pump output to load requirements

Potential Causes

The most common causes of DHS4MA on used PC400-7 excavators include:

Displacement sensor failure due to internal wear or contamination from hydraulic fluid breakdown—particularly common in machines exceeding 8,000 operating hours. The sensor harness connector corrosion is frequently found where the connector passes near the pump housing, exposed to heat and hydraulic mist.

Wiring harness damage at known rub points between the pump and the main frame, especially near the swing bearing area where vibration causes insulation wear. Faulty pump control solenoid valves can send incorrect feedback signals that trigger this code even when the sensor itself is functional.

On higher-hour used machines, mechanical wear on the swash plate linkage can prevent accurate position sensing, and contaminated hydraulic oil can damage the sensor's internal components.

How to Troubleshoot and Fix Code DHS4MA

Step 1: Connect Komatsu Diagnostic Software Use Komatsu KOMTRAX or compatible diagnostic software to read live data from the displacement sensor. Check if the sensor voltage reading falls within the normal range of 0.5-4.5 volts DC. A reading stuck at 0V or 5V indicates a wiring or sensor circuit failure.

Step 2: Inspect Wiring Harness and Connectors Physically inspect the sensor harness from the pump to the ECM, focusing on known wear points near the swing motor and along the main frame. For used excavators, look for oil contamination, cracked insulation, or abraded wires at pinch points. Disconnect the sensor connector and inspect for pin corrosion or moisture intrusion—common in machines stored outdoors.

Step 3: Test Sensor Resistance Using a digital multimeter, measure resistance across the sensor terminals (consult service manual for specific pin configuration). Typical resistance should be 500-1500 ohms at room temperature. Replace the sensor if readings are open circuit or short to ground.

Step 4: Verify Hydraulic Oil Condition Check hydraulic oil for contamination, metal particles, or varnish buildup. Degraded oil can damage the sensor's internal components. Replace filters and oil if the machine has exceeded 2,000 hours since the last service.

Step 5: Calibrate After Repair After replacing the sensor or repairing wiring, perform a pump calibration procedure using Komatsu diagnostic software to ensure proper signal recognition.

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Disclaimer: This guide provides general diagnostic information. Always consult the Komatsu PC400-7 service manual and consider professional diagnosis for complex hydraulic system issues. Improper repairs can cause severe component damage.