What is Kobelco SK460-8 Fault Code U0073?

Fault Code U0073 indicates a communication failure between the engine control module (ECM) and the controller area network (CAN) Bus 'A' communication circuit. This diagnostic trouble code (DTC) means the main ECM has lost or is experiencing intermittent communication with other critical control modules on the excavator's electronic network.

On the Kobelco SK460-8, the CAN Bus system serves as the central nervous system, allowing the ECM, hydraulic controller, monitor display, and other modules to share real-time operational data. When this communication breaks down, the machine cannot coordinate functions properly, leading to reduced performance, safety concerns, and potential system shutdowns. This code is particularly critical because it affects multiple systems simultaneously rather than a single component.

Common Symptoms

• Amber or red warning lights illuminated on the operator display, often with multiple system alerts appearing simultaneously
• Intermittent loss of throttle response or engine power fluctuations as the ECM struggles to communicate with hydraulic controls
• Inoperative or erratic gauge readings on the monitor panel, including fuel level, coolant temperature, or hydraulic pressure displays
• Engine derating or automatic shutdown in severe cases where critical communication is completely lost
• Hydraulic system malfunctions, such as slow or unresponsive boom, bucket, or swing operations due to coordination failures

Potential Causes

In used Kobelco SK460-8 excavators, U0073 typically stems from age-related electrical deterioration. The most common culprits include:

• Corroded or loose CAN Bus connectors at the ECM, particularly the 120-ohm termination resistor connections
• Damaged wiring harness along common rub points near the engine mounting brackets or beneath the operator cab where vibration causes insulation breakdown
• Failed terminating resistors in the CAN network, which are essential for signal integrity and often deteriorate in machines with 5,000+ operating hours
• Water intrusion into the main wiring harness, especially at the bulkhead connector behind the engine bay where seals commonly fail
• ECM internal communication circuit failure, though less common than external wiring issues in used equipment

How to Troubleshoot and Fix Code U0073

Step 1: Visual Inspection Begin by examining all CAN Bus connectors at the ECM and connected modules. Look specifically for green corrosion, bent pins, or moisture inside connector housings. On used SK460-8s, check the harness routing near the engine mount—this is a known wear point where cable ties deteriorate and allow harness movement.

Step 2: Test CAN Bus Resistance Using a digital multimeter, disconnect power and measure resistance across the CAN High and CAN Low terminals at the ECM connector. You should read approximately 60 ohms with all modules connected (indicating two 120-ohm terminating resistors in parallel). A reading of 120 ohms suggests one failed terminator; infinite resistance indicates an open circuit.

Step 3: Check for Voltage and Signal Quality Reconnect the system and use a multimeter or oscilloscope to verify 2.5V DC bias voltage on both CAN lines with the key on, engine off. During cranking, you should see voltage fluctuations between approximately 1.5V and 3.5V representing data transmission. No voltage fluctuation indicates the ECM isn't transmitting or a complete circuit failure.

Step 4: Inspect Harness Along Known Failure Points For used excavators, physically trace the main harness from the ECM through the engine compartment. Check where the harness passes through metal grommets or contacts the frame—wear-through exposing copper is common after years of vibration. Pay special attention to the connector behind the hydraulic pump where heat and oil mist accelerate insulation breakdown.

Step 5: Test ECM Functionality If all external wiring tests pass, the ECM's internal CAN transceiver may have failed. This requires substitution testing with a known-good ECM or factory diagnostic software like Kobelco MAPS to verify module communication capability. Before replacing an ECM on used equipment, always verify the replacement is programmed for your specific machine configuration.

Disclaimer: This guide provides general diagnostic procedures. Complex electrical issues should be diagnosed by qualified technicians with manufacturer-specific diagnostic tools. Always consult the Kobelco service manual and follow proper safety procedures when working on heavy equipment electrical systems.