Komatsu PC750-7 Fault Code E981: Complete Diagnostic Guide

What is Komatsu PC750-7 Fault Code E981?

Fault Code E981 indicates a malfunction in the hydraulic pump control system, specifically related to the pump flow control solenoid valve circuit or its associated sensors. This code is triggered when the Engine Control Module (ECM) detects an abnormal voltage, current draw, or response time from the pump control solenoid that regulates hydraulic flow based on load demand.

In the PC750-7, this system is critical for optimizing fuel efficiency and hydraulic performance. The pump flow control solenoid modulates hydraulic output to match operational requirements, preventing unnecessary engine load. When E981 appears, the machine typically enters a derate mode to protect the hydraulic system, significantly impacting productivity on job sites.

Common Symptoms

When Code E981 is active, operators typically experience:

• Reduced hydraulic power across all functions (boom, arm, bucket, swing)
• Warning light illumination on the monitor panel with fault code display
• Sluggish or unresponsive controls, particularly under heavy load conditions
• Increased fuel consumption due to inefficient pump operation
• Intermittent loss of hydraulic pressure during multi-function operations

Potential Causes

The most common technical causes for E981 on used PC750-7 excavators include:

• Solenoid valve coil failure due to age-related degradation or overheating
• Wiring harness damage at known rub points near the hydraulic pump mounting area
• Corroded or loose connector pins at the pump control solenoid (C-connector)
• ECM internal fault affecting the solenoid driver circuit
• Hydraulic contamination causing mechanical binding of the solenoid spool
• Voltage supply issues from the main power harness (should be 24V nominal)

How to Troubleshoot and Fix Code E981

Step 1: Visual Inspection Begin by inspecting the pump control solenoid connector and wiring harness for physical damage, corrosion, or oil contamination. On used excavators, check for harness wear where it routes along the pump housing—a common failure point on this model.

Step 2: Electrical Testing Using a digital multimeter, measure solenoid coil resistance (should be 3-6 ohms typically). Check supply voltage at the connector with ignition on (should read 24V). Verify ground continuity to chassis.

Step 3: Solenoid Function Test With Komatsu diagnostic software (KOMTRAX Plus), command the solenoid to actuate while monitoring current draw. Normal operation shows 2-4 amps. Erratic readings indicate internal solenoid failure.

Step 4: Harness and ECM Verification If solenoid tests pass, inspect the main harness for shorts to ground. Test ECM output using a breakout box. For used machines, consider connector cleaning with electrical contact cleaner before parts replacement—corrosion often mimics component failure.

---

Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu service manual and consider professional technician assistance for complex electrical diagnostics and repairs.