What is Caterpillar Fault Code CID733?

CID733 indicates a communication error or data mismatch in the CAN (Controller Area Network) Bus System on Caterpillar excavators. This fault code specifically signals that the Electronic Control Module (ECM) has detected inconsistent or missing data transmission between critical machine controllers, typically affecting communication between the engine controller and implement control systems.

The CAN Bus serves as the nervous system of modern Caterpillar excavators, allowing multiple electronic controllers to share real-time operational data. When CID733 triggers, it means one or more controllers are either sending corrupted messages, failing to respond within expected timeframes, or experiencing electrical interference. This is particularly critical because it can affect coordination between the engine management system, hydraulic controls, and monitoring displays, potentially causing unpredictable machine behavior or protective derates.

Common Symptoms

• Warning lights illuminated on the instrument cluster, often accompanied by a "Check Engine" or communication error message on the display
• Intermittent loss of functionality in auxiliary systems, such as unresponsive hydraulic attachments or erratic swing operation
• Engine derate mode activation, limiting power output to protect the machine from unsafe operating conditions
• Display screen anomalies, including frozen gauges, missing data fields, or complete monitor blackouts
• Inconsistent machine response where commands from joysticks or pedals produce delayed or irregular reactions

Potential Causes

• Damaged or corroded CAN Bus wiring harness, especially at known rub points near the swing bearing, boom pivot, or along the undercarriage where cables flex repeatedly
• Faulty termination resistors at either end of the CAN Bus network, which maintain proper signal integrity
• ECM or secondary controller failure, where internal electronics have degraded due to age, vibration, or moisture intrusion
• Loose or corroded connector pins at the Deutsch-style connectors commonly used in Caterpillar harnesses
• Electrical interference from aftermarket accessories, damaged alternators, or improper ground connections
• Software version mismatches between controllers after partial system updates or component replacements on used machines

How to Troubleshoot and Fix Code CID733

Step 1: Connect Diagnostic Software Use Caterpillar Electronic Technician (Cat ET) software with a compatible communication adapter. Check active and logged fault codes to identify which specific controller is reporting the communication failure. Note timestamps to determine if the fault is continuous or intermittent.

Step 2: Perform Visual Harness Inspection On used excavators, physically inspect the CAN Bus harness (typically yellow or twisted-pair wiring) for obvious damage, particularly at high-flex areas. Check all connectors for corrosion, bent pins, or moisture intrusion. Pay special attention to the main harness routing between the cab and engine compartment where chafing commonly occurs.

Step 3: Measure CAN Bus Resistance Disconnect power and use a digital multimeter to measure resistance between CAN High and CAN Low terminals at the diagnostic port. You should read approximately 60 ohms with both termination resistors in place. Readings significantly higher suggest open circuits or missing terminators; lower readings indicate short circuits.

Step 4: Check Termination Resistors Verify both 120-ohm termination resistors are present and functional at network endpoints. On many Caterpillar excavators, one resistor is in the ECM and another in the display module or implement controller.

Step 5: Isolate Faulty Controllers If wiring checks pass, systematically disconnect controllers one at a time while monitoring the network with Cat ET. When the faulty controller is disconnected, communication should stabilize for remaining modules.

Step 6: Update Software and Clear Codes Ensure all controllers run compatible firmware versions. Flash updates as needed, then clear fault codes and perform a functional test under normal operating conditions.

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Disclaimer: This guide provides general troubleshooting information for CID733 on Caterpillar excavators. Always consult the specific service manual for your machine model and serial number. If you lack proper diagnostic tools or experience with high-voltage electrical systems, contact a certified Caterpillar technician to prevent equipment damage or personal injury.