What is Kato APC150 Fault Code E99?

Kato APC150 Fault Code E99 indicates a critical communication error between the main Engine Control Module (ECM) and the hydraulic control system, specifically related to the CAN (Controller Area Network) bus failure or timeout. This code appears when the excavator's electronic systems cannot properly exchange data between the engine management system and hydraulic controllers.

On the Kato APC150 model, this fault is particularly serious because it affects the integrated control system that coordinates engine output with hydraulic demand. The CAN bus serves as the central nervous system for this excavator, transmitting real-time data between controllers at least 50 times per second. When E99 triggers, the machine typically enters a protective limp mode to prevent damage, severely limiting operational capability and potentially causing complete shutdown.

Common Symptoms

• Multiple warning lights illuminating simultaneously on the instrument cluster, including the engine and hydraulic system indicators
• Sudden loss of hydraulic power or erratic response from boom, arm, or bucket controls during operation
• Engine derating to idle or low RPM, preventing the machine from developing full power under load
• Intermittent loss of dashboard display functions, including loss of hour meter, temperature readings, or fuel gauge
• Complete machine shutdown in severe cases, requiring key cycle to restart with temporary functionality

Potential Causes

On used Kato APC150 excavators, E99 commonly stems from deteriorated CAN bus wiring harnesses, particularly where cables run near the swing bearing or along the boom base where constant flexing occurs. The termination resistors (120-ohm resistors at each end of the CAN network) can also fail over time, creating signal reflection issues.

Corroded or loose connector pins at the main ECM (located behind the operator's cab) or at the hydraulic controller junction box are frequent culprits in older machines. Water intrusion through damaged grommets compromises connection integrity.

ECM software corruption or version mismatches between controllers can occur after improper jump-starting or voltage spikes. Additionally, failed relay modules in the power distribution panel may cause intermittent voltage supply to CAN system components.

How to Troubleshoot and Fix Code E99

Step 1: Visual Inspection and Connector Check Begin by inspecting all CAN bus harness routing from the ECM to the hydraulic controller. Focus on pinch points near the battery box, swing gear housing, and boom pivot areas. Remove and clean all CAN-related connectors using electrical contact cleaner, checking for green corrosion, bent pins, or moisture. On used excavators, connector backs often show physical wear—replace any damaged terminals immediately.

Step 2: CAN Bus Electrical Testing Using a digital multimeter with ohm function, measure resistance between CAN-High and CAN-Low terminals at the ECM connector with the key off and all controllers disconnected. You should read approximately 60 ohms (two 120-ohm termination resistors in parallel). A reading of 120 ohms indicates one missing terminator; infinite resistance suggests an open circuit in the wiring. Check for short circuits to ground on each CAN wire individually—any reading below 10k ohms indicates harness damage.

Step 3: Termination Resistor and Controller Verification Locate the termination resistors at both ends of the CAN network (typically at the ECM and the furthest hydraulic controller). Test each resistor independently—they must measure exactly 120 ohms ±5%. If resistors test good, connect Kato diagnostic software (or compatible heavy equipment diagnostic tool supporting J1939 protocol) to read live CAN bus traffic and identify which controller is dropping communication.

Step 4: Voltage Supply and Ground Verification Check that all controllers receive stable 12-24V supply voltage (depending on your APC150's electrical system) with the key in the "on" position. Use your multimeter to verify less than 0.2V drop on all ground connections. On older machines, ground straps corrode at mounting points—clean contact surfaces to bare metal and apply dielectric grease before reconnecting.

Critical for Used Equipment: Before ordering expensive ECM or controller replacements, carefully examine the main wiring harness where it passes through the slewing ring area. Repeated rotation over years creates specific wear patterns on Kato models. Replace entire harness sections showing insulation cracks rather than attempting electrical tape repairs, as moisture infiltration will cause recurring faults.

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Disclaimer: This guide provides general troubleshooting information for Kato APC150 excavators. Electrical and hydraulic systems involve high voltage and pressure hazards. Always consult the official Kato service manual for your specific machine serial number and consider professional diagnosis by a certified heavy equipment technician for complex electrical issues.