Komatsu PC750LC-7 Fault Code E985: Complete Diagnostic Guide

What is Komatsu PC750LC-7 Fault Code E985?

Fault Code E985 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 PC750LC-7, this system is critical for maintaining optimal hydraulic performance across all functions. The pump flow control solenoid modulates pressure and flow based on operator demand and load conditions. When E985 appears, the machine typically enters a protective derate mode to prevent damage to the hydraulic system, significantly impacting productivity and operational efficiency.

Common Symptoms

When Code E985 is active, operators typically experience:

• Reduced hydraulic power across all functions (boom, arm, bucket, swing)
• Warning light illumination on the monitor panel with accompanying fault code display
• Sluggish or unresponsive controls, particularly under heavy load conditions
• Intermittent loss of hydraulic function that may temporarily resolve then return
• Engine derate or limited RPM as the ECM protects the hydraulic system from damage

Potential Causes

The most common technical causes for E985 in used PC750LC-7 excavators include:

• Faulty pump flow control solenoid valve due to internal coil failure or mechanical sticking
• Damaged wiring harness at known rub points near the hydraulic pump mounting area
• Corroded or loose electrical connectors on the solenoid valve circuit
• ECM internal fault or corrupted calibration data (less common)
• Low voltage supply from deteriorated battery cables or failing alternator
• Contaminated hydraulic oil causing solenoid valve spool binding

How to Troubleshoot and Fix Code E985

Step 1: Visual Inspection Begin by inspecting the pump flow control solenoid valve and its wiring harness for obvious damage. On used excavators, check for harness wear where cables contact the pump housing or frame. Clean all electrical connectors and check for corrosion or bent pins.

Step 2: Electrical Testing Using a digital multimeter, measure solenoid resistance (typically 10-30 ohms) and check for proper voltage supply (12-24V depending on system). Verify ground continuity from the solenoid to chassis ground. Use Komatsu diagnostic software (KOMTRAX or PC-based tools) to monitor real-time solenoid command signals versus actual response.

Step 3: Component Testing and Replacement If electrical values are correct, perform a functional test of the solenoid valve. For used machines, consider that internal wear may cause intermittent failures not detected by static testing. Replace the solenoid valve if resistance is out of specification or response is sluggish. After repairs, clear codes, cycle all hydraulic functions, and verify proper operation under load.

Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu service manual for your specific machine serial number and consider professional diagnosis for complex electrical or hydraulic issues.