What is Kato HD820-1 Fault Code E31?

Fault Code E31 on the Kato HD820-1 excavator indicates a hydraulic pump control system malfunction, specifically related to the main pump displacement sensor or its associated control circuit. This code is triggered when the Electronic Control Module (ECM) detects an abnormal signal from the pump angle sensor that monitors swash plate position, or when voltage readings fall outside the manufacturer's specified range of 0.5-4.5 volts.

The Kato HD820-1 utilizes a sophisticated variable displacement piston pump system that adjusts hydraulic flow based on operational demand. The pump displacement sensor communicates real-time swash plate angle data to the ECM, which then optimizes fuel consumption and hydraulic performance. When this communication fails or provides erratic data, the machine's ability to efficiently manage hydraulic power is severely compromised, potentially leading to reduced productivity and increased fuel consumption.

Common Symptoms

When Code E31 is active on your HD820-1, operators typically experience:

• Intermittent or constant hydraulic power loss across all functions (boom, arm, bucket, swing)
• Warning lamp illumination on the instrument cluster, often accompanied by an audible alarm
• Erratic hydraulic response where implement speed varies unpredictably during operation
• Engine over-revving without corresponding hydraulic output due to pump angle miscommunication
• Machine entering derate mode limiting engine RPM to protect the hydraulic system from damage

Potential Causes

The most common technical reasons for E31 code activation on used HD820-1 excavators include:

• Pump displacement sensor failure due to internal component wear or contamination from hydraulic fluid degradation
• Wiring harness damage at known rub points near the main pump mounting area where vibration causes insulation breakdown
• Corroded or loose connector pins at the sensor plug, particularly common in machines operated in high-moisture environments
• ECM voltage supply issues providing incorrect reference voltage to the sensor circuit
• Hydraulic contamination causing physical binding of the swash plate mechanism, preventing accurate sensor readings
• Previous repair attempts using non-OEM sensors with incompatible resistance values (specification: 1-5kΩ variable)

How to Troubleshoot and Fix Code E31

Step 1: Visual Inspection and Connector Assessment Begin by accessing the main hydraulic pump located on the left side of the engine. Disconnect the pump displacement sensor connector (3-pin Deutsch connector) and inspect for corrosion, bent pins, or moisture intrusion. On used excavators, this connector frequently shows green corrosion due to its proximity to the hydraulic reservoir breather. Clean contacts with electrical contact cleaner and apply dielectric grease before reconnection.

Step 2: Electrical Testing with Diagnostic Tools Using a digital multimeter, perform a resistance check across the sensor terminals with the connector disconnected and ignition off. The sensor should show variable resistance between 1-5kΩ as you manually move the pump control lever. Next, check for supply voltage at the harness side: you should measure approximately 5 volts on the reference wire (typically red/white) with ignition on. If voltage is absent or incorrect, trace the wiring harness back to the ECM, checking for breaks or shorts at common wear points where the harness passes over the pump mounting bracket.

Step 3: Sensor Replacement and System Verification If electrical values are out of specification, replace the pump displacement sensor (Kato part number HD820-PS-031 or equivalent). For used machinery, this is also an ideal time to inspect the swash plate mechanism for binding or excessive wear. After installation, clear the fault code using Kato diagnostic software or a compatible scan tool, then operate the machine through full hydraulic cycles while monitoring live data to confirm the sensor provides smooth voltage transitions between 0.5-4.5V during pump angle changes.

Critical Note for Used Equipment: Before replacing expensive components, thoroughly inspect all harness routing for modifications made by previous owners, check hydraulic fluid condition (contamination can cause mechanical sensor binding), and verify that aftermarket components haven't been installed with incorrect specifications.

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Disclaimer: This guide provides general diagnostic information for the Kato HD820-1. Always consult the official service manual for your machine's specific serial number range and consider professional diagnosis for complex hydraulic system issues. Improper repairs may void warranties or create safety hazards.