What is Komatsu PC120LC-6 Fault Code E-9?

Fault Code E-9 on the Komatsu PC120LC-6 indicates a hydraulic pump control system malfunction, specifically related to the pump flow control solenoid circuit or the engine-pump matching system. This code signals that the Electronic Control Module (ECM) has detected an abnormality in the communication or operation between the engine controller and the hydraulic pump's electro-proportional valve.

This fault is critical because the PC120LC-6 uses a sophisticated load-sensing hydraulic system where engine output must precisely match hydraulic demand. When E-9 triggers, the machine loses optimized fuel efficiency and may experience reduced hydraulic power, directly impacting excavation performance and cycle times on used equipment that already faces wear-related efficiency losses.

Common Symptoms

• Reduced hydraulic power across all functions, with noticeably slower boom, arm, and bucket movements
• Engine over-revving without corresponding hydraulic output, indicating pump flow mismatch
• Warning light illumination on the instrument cluster with possible audible alarm
• Intermittent loss of power during combined functions (e.g., simultaneous boom lift and swing)
• Increased fuel consumption as the engine-pump matching efficiency degrades

Potential Causes

The most common causes for E-9 on used PC120LC-6 excavators include:

• Pump control solenoid failure due to internal coil breakdown or valve sticking from contaminated hydraulic fluid
• Wiring harness damage at the pump mounting area where vibration causes wire chafing against the pump casing
• Corroded or loose connector pins at the X2 connector behind the operator's seat (known wear point on this model)
• ECM voltage supply issues from aging battery cables or corroded ground connections at the engine block
• Hydraulic oil contamination causing the proportional valve spool to stick, preventing proper signal response

How to Troubleshoot and Fix Code E-9

Step 1: Visual Inspection Begin by inspecting the pump control solenoid harness near the main hydraulic pump. On used PC120LC-6 models, check for wire abrasion where the harness passes over the pump mounting bracket. Examine the X2 connector for corrosion, pushed-back pins, or moisture infiltration.

Step 2: Electrical Testing Using a digital multimeter, measure resistance across the pump solenoid terminals (typically 8-12 ohms when cold). Check supply voltage at the solenoid connector with ignition on—should read approximately 12V DC. Test ground circuit continuity to the ECM.

Step 3: Solenoid Function Test With the engine running, use Komatsu diagnostic software (KOMTRAX or PC Service Tool) to command the solenoid through its full range. Listen for clicking and feel for valve movement. Replace the solenoid if no response occurs.

Step 4: Hydraulic System Check On used excavators, change the hydraulic filter and sample oil for contamination. Metal particles indicate pump wear that may be causing valve binding. Flush the control circuit if contamination is present.

Step 5: ECM and Harness Verification Inspect all engine control module grounds and verify proper voltage supply (24V on dual-battery systems). Check for corrosion at battery terminals and clean all ground connections at the engine block and frame rails.

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Disclaimer: This guide provides general troubleshooting information. Complex hydraulic and electrical system repairs should be performed by qualified technicians with appropriate diagnostic equipment. Always consult the official Komatsu service manual for your specific serial number.