Komatsu PC750-7 Fault Code E985: Complete Diagnostic Guide

What is Komatsu PC750-7 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 PC750-7, 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 on used PC750-7 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 at the solenoid valve or ECM interface
• Failed pump control sensor providing incorrect feedback to the ECM
• Low voltage supply from deteriorated battery cables or alternator issues
• ECM software corruption or internal controller fault (less common)

How to Troubleshoot and Fix Code E985

Step 1: Visual Inspection Begin by inspecting the pump flow control solenoid and its wiring harness for obvious damage. On used excavators, check for harness wear where cables contact the pump housing or frame. Examine all connectors for corrosion, bent pins, or moisture intrusion—common issues in aging machines.

Step 2: Electrical Testing Using a digital multimeter, measure resistance across the solenoid coil terminals (typically 10-30 ohms when disconnected). Check supply voltage at the connector with ignition on (should read 12-24V depending on system). Verify ground continuity is below 1 ohm.

Step 3: Diagnostic Software Analysis Connect Komatsu diagnostic software (KOMTRAX or dealer-level tools) to read live data from the pump control system. Monitor solenoid command signals versus actual response. Compare values against factory specifications in the service manual.

Step 4: Component Replacement If testing confirms solenoid failure, replace the pump flow control valve assembly. For used equipment, always replace associated O-rings and clean mounting surfaces. Clear codes and perform functional testing under load.

---

Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu PC750-7 service manual and consider professional assistance for complex hydraulic system repairs. Improper diagnosis may lead to additional component damage.