What is Kobelco SK75-8 Fault Code R174?

Fault Code R174 on the Kobelco SK75-8 excavator indicates a malfunction in the hydraulic pump discharge pressure sensor circuit. This code specifically signals that the Electronic Control Module (ECM) has detected an abnormal voltage reading from the pressure sensor that monitors the main hydraulic pump's output pressure. The sensor provides critical feedback to the machine's control system, allowing it to regulate hydraulic flow and power distribution across all hydraulic functions.

This fault is particularly significant for the SK75-8 because its sophisticated load-sensing hydraulic system relies on accurate pressure data to optimize fuel efficiency and prevent component damage. When R174 appears, the machine may enter a protective operating mode that limits hydraulic performance to prevent catastrophic pump or circuit failure.

Common Symptoms

When fault code R174 is active, operators typically experience:

• Warning light illuminated on the instrument panel with possible audible alarm
• Reduced hydraulic power across all functions (boom, arm, bucket, and swing operations feel sluggish)
• Erratic machine performance where hydraulic speed varies unpredictably during operation
• Engine RPM fluctuation as the ECM struggles to match pump demand without proper pressure feedback
• Complete hydraulic system shutdown in severe cases, forcing machine restart

Potential Causes

The most common technical causes for R174 on used SK75-8 excavators include:

• Pressure sensor failure due to internal component wear or membrane rupture (common after 5,000+ operating hours)
• Wiring harness damage at specific rub points near the pump mounting area where vibration causes insulation breakdown
• Corroded or loose electrical connectors at the sensor plug, especially on machines operated in wet or corrosive environments
• ECM voltage supply issues providing incorrect reference voltage to the sensor circuit
• Hydraulic contamination causing physical damage to the sensor's pressure-sensing element
• Previous repair attempts where aftermarket sensors with incorrect voltage ranges were installed

How to Troubleshoot and Fix Code R174

Step 1: Visual Inspection Begin by locating the hydraulic pump discharge pressure sensor mounted on the main pump body. Inspect the wiring harness from sensor to ECM for obvious damage, particularly where the harness passes near the pump drive shaft and along the frame rail. Check the connector at the sensor for corrosion, bent pins, or hydraulic oil contamination—a common issue on used excavators.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure resistance across the sensor terminals (specification typically 250-350 ohms at 20°C; consult your service manual). Test the supply voltage at the harness connector with ignition on—should read approximately 5 volts. Check ground continuity between the sensor ground wire and chassis ground (should be less than 1 ohm).

Step 3: Sensor Signal Testing Reconnect the sensor and backprobe the signal wire while operating the machine. The voltage signal should fluctuate between approximately 0.5V (low pressure) and 4.5V (high pressure) during normal hydraulic operation. A static reading or out-of-range values confirms sensor failure.

Step 4: Replacement and Verification If diagnostics confirm sensor failure, always use OEM Kobelco sensors rather than aftermarket alternatives—voltage curve differences can cause recurring codes. Before installing the new sensor, clean the mounting port and apply appropriate thread sealant. For used excavators, consider replacing the sensor connector pigtail if corrosion is present, as this prevents future intermittent faults. After installation, clear the fault code using Kobelco diagnostic software or by battery disconnect, then cycle all hydraulic functions while monitoring for code recurrence.

---

Disclaimer: This guide provides general troubleshooting information for educational purposes. Hydraulic systems operate under extreme pressure and can cause serious injury. Always consult the official Kobelco service manual for your specific serial number and consider professional diagnostic assistance for complex electrical issues or if you lack proper training and tools.