What is Komatsu PC120-6 Fault Code E315?

Komatsu PC120-6 Fault Code E315 indicates a malfunction in the hydraulic pump solenoid valve circuit, specifically related to abnormal electrical current or voltage detection within the pump control system. This code triggers when the Engine Control Module (ECM) detects an open circuit, short circuit, or improper resistance in the wiring harness connected to the main pump regulator solenoid.

The PC120-6 utilizes electronic control over its hydraulic pump displacement to optimize fuel efficiency and performance. When E315 appears, the hydraulic system may enter a default mode that limits pump output, directly impacting excavator productivity. This fault is particularly critical because the pump regulator controls digging force, swing speed, and overall hydraulic responsiveness across all functions.

Common Symptoms

• Reduced hydraulic power across all functions (boom, arm, bucket, and swing movements feel sluggish or weak)
• Warning lamp illumination on the instrument cluster, often accompanied by reduced engine RPM
• Intermittent loss of hydraulic pressure during operation, especially under heavy loads
• Engine derating or limited RPM as the ECM attempts to protect the hydraulic system
• Erratic pump response where hydraulic functions work normally then suddenly lose power

Potential Causes

The primary technical failures causing E315 on used PC120-6 excavators include:

• Damaged wiring harness between the ECM and pump solenoid, particularly at flex points near the pump mounting area where vibration causes wire fraying
• Failed pump regulator solenoid coil due to heat exposure or internal electrical breakdown (common after 8,000+ operating hours)
• Corroded electrical connectors at the solenoid or ECM interface, especially in machines exposed to wet or coastal environments
• ECM internal fault affecting the solenoid driver circuit (less common but documented in older units)
• Voltage supply issues from the main power harness, including poor ground connections at the pump assembly

How to Troubleshoot and Fix Code E315

Step 1: Connect a Komatsu diagnostic tool (or compatible scan tool) to retrieve freeze frame data and verify code E315 is current, not historical. Clear the code and attempt to reproduce the fault during operation.

Step 2: Perform a visual inspection of the pump solenoid wiring harness, focusing on wear points where the harness contacts the pump body or chassis. On used excavators, check for oil contamination on connectors, which degrades insulation. Inspect the solenoid connector for bent pins or corrosion—clean with electrical contact cleaner if needed.

Step 3: Using a digital multimeter, measure solenoid coil resistance (typically 10-15 ohms for PC120-6 pump solenoids—consult service manual for exact specification). Check voltage supply at the solenoid connector with ignition on (should read battery voltage). Test ground continuity from the solenoid case to chassis ground (should be less than 1 ohm).

Step 4: If resistance and voltage are correct, perform a solenoid functional test by commanding the solenoid on/off using diagnostic software while monitoring current draw. Replace the pump regulator solenoid if electrical parameters are abnormal or if mechanical clicking is absent during testing.

Crucial for used machines: Before replacing expensive components, thoroughly inspect harness routing for modifications from previous repairs. Check for chafed wires at the pump swivel area and verify all harness retention clips are intact to prevent future failures.

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Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu service manual for your specific machine serial number and seek professional assistance for complex electrical diagnostics or repairs involving hydraulic systems.