Sumitomo Excavator Fault Code U0073: Complete Diagnostic Guide

What is Sumitomo Excavator Fault Code U0073?

Fault Code U0073 indicates a communication loss between the Engine Control Module (ECM) and the Control Bus A network. This is a CAN (Controller Area Network) communication error that prevents critical modules from exchanging data properly.

On Sumitomo excavators, this code specifically points to a disruption in the CAN Bus communication circuit that connects the engine controller to other vital systems including the hydraulic control unit, instrument cluster, and transmission controller. This communication breakdown is critical because modern excavators rely on constant module interaction for coordinated machine operation, fuel management, and safety systems. When U0073 appears, the excavator's ability to integrate engine performance with hydraulic demand is compromised, potentially leading to reduced productivity and safety concerns.

Common Symptoms

When Code U0073 is active, operators typically experience:

• Multiple warning lights illuminated simultaneously on the dashboard, including check engine and system malfunction indicators
• Erratic engine performance such as unexpected derating, poor throttle response, or unstable idle conditions
• Hydraulic system irregularities including sluggish boom/arm movements or inconsistent attachment response
• Instrument cluster failures where gauges freeze, display incorrect readings, or go completely blank
• Difficulty starting or the engine entering a protective "limp mode" with severely limited power output

Potential Causes

The most common technical causes for U0073 on used Sumitomo excavators include:

• Damaged or corroded CAN Bus wiring harness, particularly at known rub points near the engine mounts, turbocharger area, and along the boom pivot where vibration and heat cause accelerated wear
• Loose or corroded connector terminals on the ECM, especially the multi-pin CAN Bus connector which is susceptible to moisture intrusion in older machines
• Failed termination resistors within the CAN network (typically 120-ohm resistors at network endpoints)
• ECM power supply issues including poor ground connections or voltage fluctuations from a weak battery or failing alternator
• Physical damage to control modules from engine compartment impacts, fluid contamination, or previous repair attempts

How to Troubleshoot and Fix Code U0073

Step 1: Visual Inspection Begin by thoroughly inspecting all wiring harnesses in the engine bay and cab. On used excavators, focus on areas where harnesses contact metal surfaces, pass through rubber grommets, or route near hot components. Look for chafed insulation, pinched wires, or greenish corrosion at connector pins. Check that all ECM connectors are fully seated with intact locking tabs.

Step 2: Electrical Testing Using a digital multimeter, verify battery voltage (should be 12.5-14.5V with engine running). Check the CAN Bus termination resistance by disconnecting both ends of the network and measuring between CAN-High and CAN-Low wires—you should read approximately 60 ohms (two 120-ohm resistors in parallel). Test continuity on CAN-High and CAN-Low wires separately from ECM to other modules.

Step 3: Advanced Diagnostics Connect Sumitomo diagnostic software or compatible scan tool to read network status from multiple modules. Check for additional U-codes that indicate which modules aren't communicating. Inspect ECM ground points (typically on engine block or frame rail) for tightness and corrosion—clean contact surfaces with a wire brush and apply dielectric grease.

Step 4: Component Replacement For used excavators, harness damage is the most common culprit. Replace damaged wiring sections using OEM-spec twisted-pair CAN wire, maintaining proper shielding. If connectors show corrosion, replace rather than clean them. Only replace the ECM after confirming wiring integrity, as module failures are less common than harness issues.

Disclaimer: This guide provides general diagnostic information. Always consult the official Sumitomo service manual for your specific model year and serial number. If you lack proper diagnostic tools or experience with CAN Bus systems, contact a certified Sumitomo technician to prevent costly misdiagnosis.