What is Hitachi Excavator Fault Code 13951-2?

Fault Code 13951-2 indicates a communication error or abnormal signal from the hydraulic pump control system, specifically related to the secondary pump flow control solenoid circuit. This code is triggered when the Electronic Control Module (ECM) detects an open circuit, short circuit, or out-of-range voltage in the pump pressure compensation control system.

In Hitachi excavators, this fault directly affects the machine's ability to regulate hydraulic flow and pressure efficiently. The pump control solenoid modulates hydraulic output based on load demands, and any disruption to this circuit can result in reduced performance, increased fuel consumption, and potential damage to hydraulic components. For used machines, this code often signals age-related electrical degradation or contamination in the hydraulic-electrical interface.

Common Symptoms

• Reduced hydraulic power across all functions (boom, arm, bucket, swing)
• Erratic or sluggish hydraulic response, particularly under heavy loads
• Warning light illuminated on the instrument panel (typically a hydraulic system icon)
• Increased engine RPM without corresponding increases in hydraulic performance
• Intermittent loss of hydraulic function that may reset after machine shutdown

Potential Causes

The following are the most common technical causes for Code 13951-2 in used Hitachi excavators:

• Damaged or corroded wiring harness at the pump control solenoid connector (common wear point due to vibration and heat exposure)
• Failed pump pressure control solenoid due to internal coil breakdown or mechanical sticking
• Contaminated hydraulic oil causing solenoid valve malfunction or sensor interference
• ECM voltage supply issues, including poor ground connections or battery voltage fluctuations
• Worn connector pins at the main pump harness junction (typical in machines with 5,000+ operating hours)
• Hydraulic oil temperature sensor malfunction providing incorrect data to the ECM

How to Troubleshoot and Fix Code 13951-2

Step 1: Connect a Hitachi diagnostic software tool (Dr.EX or compatible scan tool) to retrieve freeze frame data and verify the fault is current, not historic.

Step 2: Perform a visual inspection of the pump control solenoid wiring harness. Check for chafing against the pump housing, heat damage near the engine block, and corrosion at all connectors. In used excavators, harness routing often shifts over time, creating new wear points.

Step 3: Using a digital multimeter, measure resistance across the solenoid coil terminals (typically 8-15 ohms for Hitachi pumps). Check for supply voltage (should be 12-24V depending on model) and verify ground continuity (less than 1 ohm resistance).

Step 4: Inspect hydraulic oil quality and temperature. Contaminated or degraded oil can cause solenoid sticking. Replace filters and flush the system if oil shows metallic particles or water contamination.

Step 5: If electrical values are within specification but the code persists, replace the pump control solenoid valve and clear codes. Test under load conditions to confirm repair.

Disclaimer: This guide provides general troubleshooting information. Always consult your machine's service manual and consider professional diagnostic assistance for complex hydraulic-electrical issues, especially on used equipment with unknown maintenance history.