What is Caterpillar Fault Code CID5855?

Caterpillar Fault Code CID5855 indicates a communication error or data link failure within the machine's Controller Area Network (CAN) system, specifically related to a missing or intermittent message from a connected electronic control module. This fault occurs when the primary Electronic Control Module (ECM) fails to receive expected data packets from another controller on the network within the designated timeframe.

The CAN bus system is the nervous system of modern Caterpillar excavators, allowing various controllers—including the engine ECM, hydraulic controller, display module, and transmission control—to share critical operational data. When CID5855 triggers, it signals that one of these modules has stopped communicating properly, which can compromise coordinated machine functions. For used excavators, this fault is particularly concerning because it often stems from accumulated wear on electrical connections, corroded pins, or damaged wiring harnesses that have deteriorated over thousands of operating hours.

Common Symptoms

• Warning lights or messages displayed on the operator monitor indicating a communication fault or system error
• Reduced machine performance or entry into derate mode, limiting engine power or hydraulic functions as a protective measure
• Intermittent gauge failures where display readings freeze, fluctuate erratically, or go blank temporarily
• Erratic machine behavior such as unexpected hydraulic responses or inconsistent throttle control due to lost coordination between systems
• Multiple simultaneous fault codes appearing alongside CID5855, as the communication breakdown affects various subsystems

Potential Causes

The most common technical causes for CID5855 in used Caterpillar excavators include:

• Damaged or corroded wiring harnesses, particularly at flex points near the swing bearing, boom base, or cab mounting areas where repeated movement causes insulation wear
• Loose or corroded connector pins on CAN bus connections, especially the Deutsch-style connectors exposed to moisture intrusion over time
• Failed electronic control module, where an individual controller has experienced internal failure and stopped transmitting data
• Low voltage conditions from a weak battery or failing alternator, causing modules to drop offline intermittently
• Improper termination resistors on the CAN network, which may have been removed or damaged during previous repairs or aftermarket equipment installations
• ECM software corruption or outdated firmware versions that create compatibility issues between controllers

How to Troubleshoot and Fix Code CID5855

Step 1: Connect Diagnostic Software Use Caterpillar Electronic Technician (Cat ET) diagnostic software with the appropriate communication adapter. Check the active and logged fault codes, and identify which specific module is reporting the communication loss. The fault description will typically indicate which controller address is missing from the network.

Step 2: Perform Visual Harness Inspection On used excavators, physically inspect all CAN bus wiring harnesses for visible damage, particularly focusing on high-flex areas. Look for abraded insulation, pinched wires at mounting brackets, and evidence of rodent damage. Check all connectors for bent pins, corrosion (green or white deposits), or moisture infiltration. Pay special attention to connections near the swing bearing where harnesses experience the most mechanical stress.

Step 3: Test Electrical Connections Using a digital multimeter, verify proper CAN High and CAN Low voltage levels at the suspect module connector. With ignition on and engine off, you should typically measure approximately 2.5V on both CAN High and CAN Low lines (at rest). Measure resistance between CAN High and CAN Low—you should read approximately 60 ohms if termination resistors are properly installed at network endpoints.

Step 4: Check Power Supply and Grounds Verify that the affected module receives proper battery voltage (typically 24V on larger excavators) and has solid ground connections. Corroded ground straps are extremely common on used machines and can cause intermittent communication failures. Clean all ground connection points to bare metal and apply dielectric grease.

Step 5: Swap or Replace Suspect Module If wiring and power supply check out, the electronic control module itself may have failed. Before purchasing expensive replacement controllers, consider swapping with a known-good module from another circuit (if applicable) to confirm the diagnosis. For used excavators, also verify that all modules have compatible software versions using Cat ET.

Critical Note for Used Equipment: Before replacing any modules, thoroughly clean and inspect all connector seals and backshells. Apply dielectric grease to connections after cleaning to prevent future corrosion—this simple step often resolves intermittent CID5855 faults without parts replacement.

---

Disclaimer: This guide provides general troubleshooting information for Caterpillar CID5855 faults. Always consult your machine's specific service manual and consider professional diagnostic services from a certified Caterpillar technician for complex electrical issues. Improper diagnosis can lead to unnecessary parts replacement and extended downtime.