Komatsu PC800-7 Fault Code E985: Complete Diagnostic Guide

What is Komatsu PC800-7 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 PC800-7, this system is critical for maintaining optimal hydraulic pressure and flow to all work functions. The pump flow control solenoid modulates pump displacement based on operator demand and load conditions. When E985 appears, the machine typically enters a protective derate mode to prevent hydraulic system damage, 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 RPM fluctuations as the ECM attempts to compensate for hydraulic system irregularities

Potential Causes

The most common technical causes for E985 on used PC800-7 excavators include:

• Solenoid valve coil failure due to overheating or internal short/open circuits
• Wiring harness damage at known rub points near the pump mounting area or along the main chassis harness
• Corroded or loose connector pins at the solenoid valve connector (especially in machines exposed to moisture)
• ECM internal fault affecting the solenoid driver circuit
• Hydraulic contamination causing mechanical binding of the solenoid spool
• Voltage supply issues from damaged power distribution circuits or poor ground connections

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 rails. Examine connector pins for corrosion, bent terminals, or moisture intrusion.

Step 2: Electrical Testing Using a digital multimeter, measure solenoid coil resistance (typically 3-8 ohms for Komatsu solenoids). Check supply voltage at the connector with ignition on (should read 12-24V depending on system). Verify ground circuit continuity with less than 1 ohm resistance.

Step 3: Solenoid Function Test With Komatsu diagnostic software (KOMTRAX Plus) connected, perform an active solenoid test. Monitor current draw (typically 1.5-2.5 amps). Listen for audible clicking indicating mechanical operation.

Step 4: Harness and ECM Verification If solenoid tests normal, inspect the entire harness route for chafing or internal wire breaks. Test ECM output at the controller connector. For used machines, corrosion inside multi-pin connectors is common—clean with electrical contact cleaner and apply dielectric grease.

Step 5: Component Replacement Replace faulty components starting with the most likely cause. On high-hour machines, consider replacing both the solenoid and its connector as preventive maintenance.

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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 seek qualified technician assistance for complex repairs.