What is Caterpillar Fault Code E1173?

Caterpillar Fault Code E1173 indicates a communication error or data link failure between the Engine Control Module (ECM) and other critical machine control systems. This diagnostic trouble code specifically signals that the ECM has detected an abnormal or missing message on the CAN (Controller Area Network) bus, which is the digital communication highway connecting various electronic control units throughout the excavator.

This fault is critical for Caterpillar excavators because modern machines rely heavily on continuous data exchange between the engine controller, hydraulic control system, display monitor, and other electronic modules. When E1173 appears, the ECM cannot properly coordinate engine performance with hydraulic demands, potentially causing the machine to enter a derate mode or limiting operational capabilities to protect components from damage. For used excavators, this code often surfaces due to age-related deterioration of wiring harnesses, corrosion in connectors, or failing control modules that have accumulated thousands of operating hours.

Common Symptoms

• Warning lights illuminated on the operator display, often accompanied by a check engine lamp or diagnostic indicator
• Reduced engine power or machine entering a derate mode, limiting RPM and hydraulic function performance
• Intermittent loss of display information, with gauge readings freezing or disappearing temporarily
• Erratic hydraulic response or unexpected changes in machine behavior during operation
• Communication errors displayed on Cat ET (Electronic Technician) diagnostic software when attempting to connect

Potential Causes

The most common technical causes for E1173 in used Caterpillar excavators include:

• Damaged or corroded wiring harness connections, particularly at junction points behind the cab or near the engine compartment where vibration and moisture exposure are highest
• Faulty CAN bus termination resistors (120-ohm resistors at network endpoints) causing signal reflection and communication failures
• Failing ECM or display monitor with degraded internal communication circuits due to age and thermal cycling
• Loose or corroded ground connections affecting the entire electrical system's reference voltage
• Damaged CAN data lines (typically twisted-pair wiring) from pinching, rubbing against frame components, or rodent damage—common in machines stored outdoors
• Voltage irregularities from a weak battery, failing alternator, or poor battery cable connections affecting module operation

How to Troubleshoot and Fix Code E1173

Step 1: Perform Initial Visual Inspection Begin by thoroughly inspecting all visible wiring harnesses and connectors between the ECM, display panel, and other control modules. Focus on known rub points where harnesses pass through bulkheads or near moving components. Check for physical damage, corrosion (white or green deposits), bent pins, or moisture intrusion in connector bodies. On used excavators, pay special attention to harness sections that show wear from years of vibration.

Step 2: Check Power Supply and Grounds Using a digital multimeter, verify battery voltage (should be 12.5-14.5V with engine running) and inspect all ground connections to the frame and engine block. Poor grounds are frequent culprits in communication errors. Clean ground contact points with a wire brush and apply dielectric grease. Check for voltage drops across ground connections—readings above 0.2V indicate resistance problems.

Step 3: Test CAN Bus Integrity With Cat ET diagnostic software connected, monitor live CAN bus communication and check for network errors or missing module addresses. Using a multimeter set to resistance (Ω), measure between CAN High and CAN Low pins at the diagnostic connector with all modules connected and ignition off—you should read approximately 60 ohms (two 120-ohm terminating resistors in parallel). Readings significantly higher suggest open circuits or missing termination; lower readings indicate short circuits.

Step 4: Isolate Faulty Components Systematically disconnect individual modules one at a time while monitoring the CAN network with diagnostic software to identify which component is disrupting communication. For used machines, replace any connectors showing corrosion before condemning expensive modules. If the fault persists after harness repair, the ECM or another control module may require replacement—verify with Caterpillar dealer support before purchasing parts.

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Disclaimer: This guide provides general troubleshooting information for Caterpillar fault code E1173. Always consult your machine's service manual and consider professional diagnostic assistance from certified Caterpillar technicians, especially when dealing with complex electronic systems on used equipment with unknown service history.