What is Komatsu PC450-7 Fault Code DHS3MA?

Fault Code DHS3MA indicates a malfunction in the hydraulic oil temperature sensor circuit within the Komatsu PC450-7's hydraulic system monitoring network. This code specifically triggers when the Engine Control Module (ECM) detects an abnormal voltage signal from the hydraulic oil temperature sensor, typically reading either an open circuit, short to ground, or implausible temperature values outside the sensor's operational range of -40°C to 150°C.

This fault is critical for the PC450-7 because hydraulic oil temperature directly affects system viscosity, component wear rates, and overall hydraulic efficiency. The Komatsu KOMTRAX monitoring system relies on accurate temperature data to prevent thermal damage to pumps, motors, and seals. When DHS3MA activates, the ECM may default to conservative operational parameters, potentially limiting machine performance to protect hydraulic components.

Common Symptoms

• Hydraulic oil temperature warning light illuminated on the instrument cluster, often accompanied by an audible alarm
• Reduced hydraulic response or slower cycle times as the ECM enters a protective derate mode
• KOMTRAX diagnostic display showing abnormal temperature readings (typically -40°C or 150°C+ when sensor has failed)
• Intermittent code activation during machine warm-up or operation, especially on used excavators with corroded connections
• Error code stored in ECM memory even after temperature normalizes, requiring manual reset

Potential Causes

The most common causes for DHS3MA on used PC450-7 excavators include:

• Hydraulic oil temperature sensor failure due to internal element degradation (common after 8,000+ operating hours)
• Damaged wiring harness between the sensor and ECM, particularly at known rub points near the hydraulic tank and along the right-side chassis rail
• Corroded or moisture-contaminated connectors at the sensor plug (3-pin Deutsch connector), especially on machines operated in coastal or high-humidity environments
• ECM internal circuit issues affecting the 5-volt reference voltage supply to the sensor
• Improper sensor installation or overtightened threads causing internal damage during previous maintenance

How to Troubleshoot and Fix Code DHS3MA

Step 1: Visual Inspection Locate the hydraulic oil temperature sensor on the left side of the hydraulic oil tank. Inspect the 3-pin connector for corrosion, bent pins, or oil contamination. On used excavators, check the entire wiring harness from sensor to ECM for abrasion points, particularly where it passes through the frame near the swing motor.

Step 2: Electrical Testing Disconnect the sensor connector. Using a digital multimeter, measure resistance across the sensor terminals. A functioning sensor should read approximately 2,500 ohms at 20°C. Verify the ECM supplies 5-volt reference voltage at the harness-side connector with ignition on. Resistance outside 500-10,000 ohms or zero reference voltage indicates component failure.

Step 3: Signal Wire Continuity Check continuity and resistance (should be <5 ohms) between the sensor connector and **ECM pins C-47 and C-48**. Inspect for **shorts to ground** by measuring resistance between signal wires and chassis ground (should read >10 megohms). Replace damaged sections of harness using OEM-spec shielded wire.

Step 4: Sensor Replacement and Calibration If testing confirms sensor failure, replace with Komatsu part number 7861-93-3320 (verify compatibility). Apply anti-seize compound to threads, torque to 15-20 N⋅m. Clear codes using Komatsu diagnostic software and verify live temperature readings match ambient conditions before returning to service.

---

Disclaimer: This guide provides general troubleshooting information. Always consult the Komatsu PC450-7 service manual and consider professional diagnostic assistance for complex electrical issues. Improper repairs may void warranties or create safety hazards.