Komatsu PC800SE-7 Fault Code E985: Complete Diagnostic Guide

What is Komatsu PC800SE-7 Fault Code E985?

Fault Code E985 indicates a malfunction in the hydraulic pump control system, specifically related to the main pump regulator solenoid circuit or its associated control signals. This code is triggered when the Engine Control Module (ECM) detects an abnormal voltage, current draw, or communication failure within the pump control circuitry.

The PC800SE-7 relies on precise hydraulic pump regulation to maintain optimal flow and pressure across all systems. When E985 appears, the ECM recognizes that the main pump regulator solenoid isn't responding correctly to commanded inputs. This directly impacts machine performance, as the hydraulic system may enter a protective derate mode to prevent component damage. For used excavators, this code often signals age-related electrical degradation rather than catastrophic mechanical failure.

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 possible audible alarm
• Erratic pump response or inconsistent flow during combined operations
• Engine derate mode limiting RPM to protect the hydraulic system
• Intermittent code appearance that may clear and return, especially during temperature changes

Potential Causes

The most common technical reasons for E985 on used PC800SE-7 excavators include:

• Solenoid coil failure in the main pump regulator due to heat cycling and age
• Wiring harness damage at known rub points near the pump mounting area or along the chassis rail
• Connector corrosion at the pump regulator plug, particularly on machines operating in wet/coastal environments
• ECM internal fault affecting the pump control output driver circuit
• Voltage supply issues from damaged power distribution harness or poor ground connections
• Contaminated hydraulic oil causing mechanical binding of the regulator spool

How to Troubleshoot and Fix Code E985

Step 1: Visual Inspection Begin with a thorough inspection of the pump regulator solenoid and its wiring harness. On used excavators, check for harness chafing where cables route near the pump housing and frame rails. Inspect the connector pins for corrosion, bent terminals, or oil contamination. Clean connections with electrical contact cleaner.

Step 2: Electrical Testing Using a digital multimeter, measure solenoid resistance at the connector (typically 8-15 ohms for Komatsu regulators). Check supply voltage with ignition on—should read battery voltage (24V system). Verify ground continuity to chassis with less than 0.5 ohms resistance.

Step 3: Dynamic Testing Connect Komatsu diagnostic software (KOMTRAX or compatible scan tool) to monitor real-time solenoid command signals versus actual response. Command the pump regulator through various positions while monitoring current draw (should be 0.5-2.0 amps depending on position). Erratic readings indicate solenoid failure.

Step 4: Component Replacement If testing confirms solenoid failure, replace the pump regulator assembly. For used machines, always replace the connector pigtail simultaneously, as internal wire fatigue often accompanies solenoid issues. After replacement, perform hydraulic system calibration using diagnostic software.

Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu service manual for your specific serial number and consider professional diagnosis for complex electrical issues or if unfamiliar with high-voltage systems.