What is Kato HD820-2 Fault Code E90?

Fault Code E90 on the Kato HD820-2 excavator indicates a malfunction in the hydraulic pump displacement control system, specifically related to the electronic proportional control solenoid or its circuit. This code is triggered when the Electronic Control Module (ECM) detects abnormal voltage, current draw, or response time from the pump control solenoid that regulates hydraulic flow and pressure.

This system is critical for the HD820-2's performance because it directly controls how much hydraulic power is delivered to all functions—boom, arm, bucket, swing, and travel. When E90 appears, the machine typically enters a derate mode to prevent damage to the hydraulic pump, significantly reducing operational efficiency and potentially causing costly downtime on job sites.

Common Symptoms

When Code E90 is active on your Kato HD820-2, operators typically experience:

• Reduced hydraulic power across all functions, with noticeably slower cycle times
• Intermittent or complete loss of specific hydraulic functions (often boom or arm movement)
• Warning light illumination on the instrument cluster, sometimes accompanied by audible alarms
• Engine RPM fluctuations or unusual sounds from the hydraulic pump area during operation
• Erratic machine response where hydraulic functions work normally for brief periods then suddenly lose power

Potential Causes

The most common technical causes for Code E90 on used HD820-2 excavators include:

• Proportional control solenoid failure due to internal coil degradation or mechanical wear from contaminated hydraulic oil
• Wiring harness damage at known rub points near the pump mounting area or main chassis harness routing
• Corroded or loose electrical connectors at the solenoid or ECM connections, especially on machines with high hours
• ECM voltage supply issues caused by failing alternator output or damaged power distribution circuits
• Contaminated hydraulic oil causing the solenoid spool to stick or respond sluggishly
• Failed pressure sensors in the pump control circuit providing incorrect feedback to the ECM

How to Troubleshoot and Fix Code E90

Step 1: Initial Visual Inspection Begin by inspecting the proportional control solenoid mounted on the main hydraulic pump. Check all electrical connectors for corrosion, bent pins, or moisture intrusion—common issues on used excavators. Examine the wiring harness from the solenoid to the ECM for chafing, particularly where it passes near moving components or metal edges.

Step 2: Electrical Testing Using a digital multimeter, check the solenoid resistance. The Kato HD820-2 proportional solenoid typically reads between 8-12 ohms at room temperature. Next, verify battery voltage (12-14V) is reaching the solenoid connector with the key on. Check for short circuits to ground by measuring resistance between each solenoid wire and chassis ground (should read infinite resistance).

Step 3: Dynamic Circuit Testing With the engine running, use a Kato diagnostic tool or compatible scan tool to command the solenoid through its range while monitoring actual current draw. Normal operation should show 0.8-1.2 amps varying smoothly. Erratic readings or no response indicates solenoid failure. For used excavators, also inspect the hydraulic oil filter for metal contamination that could indicate pump wear affecting solenoid operation.

Step 4: Component Replacement and Verification If testing confirms solenoid failure, replace it with a genuine Kato part to ensure proper specifications. On older machines, also replace the connector pigtail if any corrosion is present. After replacement, clear codes, perform a complete hydraulic system function test, and verify oil cleanliness meets ISO 4406 18/16/13 standards to prevent repeat failures.

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Disclaimer: This guide provides general troubleshooting information for Kato HD820-2 excavators. Hydraulic and electrical systems operate under high pressure and voltage. Always consult your machine's service manual and consider professional diagnostic assistance for complex repairs, especially on used equipment with unknown service history.