Komatsu PC750-7 Fault Code E986: Complete Diagnostic Guide

What is Komatsu PC750-7 Fault Code E986?

Fault Code E986 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 Electronic Control Module (ECM) detects an abnormal voltage, current draw, or response time from the pump control solenoid that regulates hydraulic flow distribution.

In the PC750-7, this system is critical for maintaining optimal hydraulic performance across all functions. The pump flow control solenoid adjusts displacement based on load demands, directly affecting fuel efficiency and operational responsiveness. When E986 appears, the machine typically enters a derated mode to prevent hydraulic system damage, significantly impacting productivity.

Common Symptoms

When Code E986 is active, operators typically experience:

• Reduced hydraulic power across all functions (boom, arm, bucket, swing)
• Sluggish or unresponsive controls, particularly under heavy load conditions
• Warning light illumination on the monitor panel with possible audible alarm
• Increased fuel consumption due to inefficient pump operation
• Intermittent loss of hydraulic function that may worsen as the machine warms up

Potential Causes

The most common technical causes for E986 on used PC750-7 excavators include:

• Solenoid valve coil failure due to age-related insulation breakdown 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 series)
• ECM internal fault affecting the solenoid driver circuit
• Contaminated hydraulic oil causing mechanical sticking of the solenoid spool
• Voltage supply issues from the main power harness or ground connections

How to Troubleshoot and Fix Code E986

Step 1: Visual Inspection Begin by inspecting the pump control solenoid connector and wiring harness for obvious damage, corrosion, or oil contamination. On used excavators, check for harness wear where it passes near the pump housing—this is a known failure point on the PC750-7.

Step 2: Electrical Testing Using a digital multimeter, measure solenoid coil resistance (typically 3-7 ohms at 20°C). Check supply voltage at the connector with ignition on (should read 24V DC). Verify ground circuit continuity with less than 1 ohm resistance.

Step 3: Solenoid Function Test With Komatsu KOMTRAX diagnostic software or compatible scan tool, perform an active test of the solenoid. Listen for audible clicking and measure current draw (typically 2-4 amps). Replace the solenoid if it fails to actuate or draws excessive current.

Step 4: Harness and ECM Verification If the solenoid tests good, inspect the entire harness for internal breaks using a continuity tester. For persistent codes after component replacement, ECM reprogramming or replacement may be necessary—consult wiring diagrams for proper pin identification.

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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 consider professional assistance for complex electrical diagnostics.