What is Komatsu PC300-7 Fault Code E-31?

Fault Code E-31 on the Komatsu PC300-7 indicates a malfunction in the pump control solenoid valve circuit within the hydraulic system. This code triggers when the Engine Control Module (ECM) detects an abnormal electrical signal—either an open circuit, short circuit, or improper voltage—in the wiring or solenoid controlling hydraulic pump output.

The pump control solenoid valve regulates hydraulic flow and pressure based on operator demand and engine load conditions. On the PC300-7, this system is critical for maintaining optimal fuel efficiency while delivering the precise hydraulic power needed for digging, lifting, and swing operations. When E-31 appears, the machine may enter a derate mode or limit hydraulic performance to protect the pump and engine from damage due to uncontrolled flow rates.

Common Symptoms

When Code E-31 is active on your Komatsu PC300-7, operators typically experience:

• Reduced hydraulic power across all functions (boom, arm, bucket, swing)
• Intermittent or complete loss of hydraulic response during operation
• Monitor display warning showing E-31 with a possible pump icon or warning light
• Engine running normally but excavator unable to perform work efficiently
• Erratic hydraulic operation, especially when the machine is cold or after extended idle periods

Potential Causes

The most common technical reasons for E-31 on used PC300-7 excavators include:

• Damaged wiring harness near the pump control solenoid valve, particularly where the harness passes over the engine or pump housing (known rub point on this model)
• Failed pump control solenoid valve due to internal coil breakdown or mechanical sticking from contaminated hydraulic oil
• Corroded or loose electrical connectors at the solenoid valve or ECM connection points
• ECM internal fault or software glitch (less common but possible on high-hour machines)
• Low voltage supply from aging battery or poor ground connections affecting solenoid operation
• Contaminated hydraulic oil causing the solenoid spool to stick, creating electrical feedback

How to Troubleshoot and Fix Code E-31

Step 1: Visual Inspection and Connector Check Begin by locating the pump control solenoid valve mounted on the main hydraulic pump. Inspect the wiring harness from the solenoid back to the ECM for obvious damage, chafing, or exposed wires—particularly where the harness contacts metal surfaces or moves with engine vibration. On used excavators, check all electrical connectors for corrosion, bent pins, or oil contamination. Clean connectors with electrical contact cleaner and ensure tight connections.

Step 2: Electrical Testing with Multimeter Using a digital multimeter, perform a resistance check on the solenoid coil. Disconnect the harness connector at the solenoid and measure resistance across the solenoid terminals. Typical resistance should be 10-30 ohms (consult your service manual for exact specifications). An open circuit (infinite resistance) or short circuit (near-zero resistance) indicates solenoid failure. Also check for voltage supply at the connector with ignition on—should read approximately 12-24V DC depending on system design.

Step 3: Ground Circuit and Harness Continuity Test the ground circuit integrity by checking continuity between the solenoid ground wire and a known good chassis ground. High resistance (above 1 ohm) indicates a poor ground connection. On older PC300-7 machines, examine the harness for internal wire breaks by performing a wiggle test while monitoring continuity—flex the harness at suspected wear points while watching your meter for intermittent opens.

Step 4: Solenoid Replacement or ECM Diagnosis If electrical tests confirm solenoid failure, replace the pump control solenoid valve with a genuine Komatsu or OEM-equivalent part. After replacement, clear the fault code using Komatsu diagnostic software (KOMTRAX or PC-based software) and test operation. If the solenoid and wiring test normal but E-31 persists, ECM diagnosis may be required using factory diagnostic tools to check internal fault memory and output driver circuits.

Used Excavator Specific Considerations: Before replacing expensive components, thoroughly inspect for wear-related issues common in high-hour machines: harness insulation breakdown from heat cycling, connector pin spread from repeated connections, and hydraulic oil contamination that may cause mechanical solenoid binding rather than electrical failure.

---

Disclaimer: This guide provides general troubleshooting information for educational purposes. Hydraulic and electrical system diagnosis can be complex and potentially dangerous. Always consult your Komatsu service manual, manufacturer technical support, or a certified heavy equipment technician before performing repairs, especially on used machinery where unknown modifications or previous damage may exist.