What is Caterpillar Fault Code CID957?

CID957 indicates a communication failure or data link error within the Caterpillar machine's Controller Area Network (CAN) system. This fault code specifically signals that one or more electronic control modules (ECMs) are not communicating properly with the main monitoring system or other controllers on the network.

In Caterpillar excavators, the CAN bus system serves as the central nervous system, allowing various electronic controllers—including the engine ECM, hydraulic controller, and display module—to share critical operational data. When CID957 triggers, it means the machine has detected missing or corrupted messages between these modules. This is particularly critical because modern excavators rely on seamless communication between controllers to optimize fuel efficiency, manage hydraulic flow, and maintain safety protocols. Without proper data exchange, the machine may enter derate mode or experience reduced functionality to protect components from potential damage.

Common Symptoms

• Warning lights or messages appearing on the operator display indicating communication errors or system faults
• Reduced engine power or derate mode activation, limiting machine performance to prevent further issues
• Intermittent or complete loss of certain functions like hydraulic responsiveness or monitoring gauge readings
• Display screen freezing or showing incorrect/missing operational data
• Engine failing to start or shutting down unexpectedly due to communication handshake failures

Potential Causes

The most common causes of CID957 in used Caterpillar excavators include:

• Damaged or corroded CAN bus wiring harness, especially at known rub points near the turret rotation area or along the boom
• Loose or corroded electrical connectors at ECM modules, particularly the 9-pin or 12-pin CAN communication connectors
• Failed electronic control module (ECM, hydraulic controller, or instrument cluster) unable to transmit/receive data
• Low voltage or battery issues affecting the entire electrical system and causing communication dropouts
• Water intrusion into connector housings, common in excavators operating in wet environments
• Faulty termination resistors on the CAN network causing signal reflection and data corruption

How to Troubleshoot and Fix Code CID957

Step 1: Visual Inspection of Wiring and Connectors Begin by thoroughly inspecting all CAN bus wiring harnesses throughout the machine. Pay special attention to areas where harnesses pass through moving joints or contact metal surfaces. On used excavators, check for harness wear, exposed wires, or signs of previous repairs. Examine all connector pins for corrosion, bent terminals, or moisture intrusion. Clean connectors with electrical contact cleaner and apply dielectric grease.

Step 2: Voltage and Resistance Testing Using a digital multimeter, verify battery voltage is at least 12.5V with the key off and above 13.5V with the engine running. Check the CAN bus termination resistance by disconnecting both ends of the network and measuring between CAN High and CAN Low pins—you should read approximately 60 ohms (two 120-ohm resistors in parallel). Incorrect readings indicate faulty termination resistors or a short/open circuit.

Step 3: Diagnostic Software Analysis Connect Caterpillar Electronic Technician (Cat ET) or equivalent diagnostic software to identify which specific module is failing to communicate. The software will show active and inactive nodes on the network. If a particular ECM doesn't appear, focus troubleshooting on that module's power supply, ground connections, and CAN wiring. For used machines, consider that ECM internal failures become more common after 8,000+ operating hours.

Step 4: Component Replacement and Verification If wiring and connections test properly, the issue likely resides in a failed control module. Before replacing expensive ECMs, swap suspect modules with known-good units if available for testing. After repairs, clear fault codes, cycle the key, and operate the machine through various functions while monitoring for code recurrence.

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Disclaimer: This guide provides general troubleshooting information for Caterpillar CID957. Always consult the specific service manual for your excavator model and consider professional diagnostic assistance for complex electrical issues. Improper repairs can cause additional damage or safety hazards.