What is Caterpillar Fault Code CID1668?

Caterpillar fault code CID1668 indicates a communication error or data link failure within the machine's Controller Area Network (CAN) bus system. This diagnostic trouble code specifically signals that one or more electronic control modules (ECMs) are not communicating properly with each other or with the main machine controller.

The CAN bus system serves as the central nervous system for modern Caterpillar excavators, allowing critical components like the engine ECM, hydraulic controller, and display monitor to exchange data continuously. When CID1668 activates, it means this communication network has been interrupted or degraded, preventing proper coordination between systems. This is particularly critical because the machine's performance, safety features, and diagnostic capabilities all depend on reliable controller communication. Without proper data exchange, the excavator cannot optimize fuel delivery, hydraulic response, or emissions control, potentially leading to reduced efficiency and operator safety concerns.

Common Symptoms

• Warning light illumination on the instrument cluster, often accompanied by a malfunction indicator lamp (MIL) or check engine light
• Reduced engine power or derate mode activation, where the machine limits performance to prevent potential damage
• Erratic hydraulic behavior including inconsistent boom, stick, or bucket response due to interrupted communication between controllers
• Inoperative or frozen display screen showing outdated information or inability to access diagnostic menus
• Intermittent loss of auxiliary functions such as climate control, monitoring systems, or attachment controls

Potential Causes

The most common technical causes for CID1668 in used Caterpillar excavators include:

• Damaged or corroded CAN bus wiring harness, particularly at known rub points near the swing bearing, boom base, or cab mounting areas where flexing occurs
• Loose or corroded electrical connectors at ECM junction points, especially the 9-pin or 37-pin Deutsch connectors prone to moisture intrusion
• Failed termination resistors at either end of the CAN network (typically 120-ohm resistors that maintain proper signal integrity)
• ECM power supply issues including weak batteries, failing alternators, or poor ground connections affecting controller operation
• Internal ECM failure or software corruption, more common in machines with over 8,000 operating hours
• Aftermarket component installation that improperly interfaces with the CAN bus network without correct protocols

How to Troubleshoot and Fix Code CID1668

Step 1: Perform Visual Inspection Begin by thoroughly inspecting all visible wiring harnesses along the CAN network pathways. Pay special attention to areas where harnesses route near moving components, sharp edges, or through the swing bearing passage. On used excavators, look for abraded wire insulation, pinched cables, or evidence of previous repairs with electrical tape. Check all connector terminals for bent pins, corrosion (green or white deposits), or moisture intrusion. Clean connectors with electrical contact cleaner and apply dielectric grease.

Step 2: Test CAN Bus Integrity Using a digital multimeter, measure the resistance between the CAN-High and CAN-Low terminals at the diagnostic connector (typically located near the cab). With the key off and all modules connected, you should read approximately 60 ohms (two 120-ohm termination resistors in parallel). A reading of 120 ohms indicates one missing termination resistor; infinite resistance suggests an open circuit in the network. Check voltage levels with the key on: CAN-High should read approximately 2.5-3.5V and CAN-Low around 1.5-2.5V at idle state.

Step 3: Isolate the Faulty Module Use Caterpillar Electronic Technician (Cat ET) diagnostic software to identify which specific controller is not responding. Disconnect modules one at a time, starting with non-critical systems, to determine if a single failed ECM is pulling down the entire network. For used machines, prioritize checking the hydraulic controller and engine ECM as these experience the most environmental stress. Inspect the machine ground straps between the chassis, engine block, and cab—corroded grounds are a frequent cause of communication failures in older equipment.

Step 4: Address Specific Findings If wiring damage is found, repair using proper CAN-rated twisted-pair cable (not standard wire) and seal all connections with heat-shrink tubing. Replace any corroded connectors rather than attempting to clean severely damaged terminals. If termination resistors are missing or failed, install correct 120-ohm, 1/4-watt resistors at network endpoints. For intermittent codes on used excavators, secure harnesses away from wear points using proper standoffs and inspect rubber grommets that may have hardened with age.

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Disclaimer: This guide provides general diagnostic information for Caterpillar fault code CID1668. Excavator electrical systems are complex and vary by model year and configuration. Always consult the specific service manual for your machine and consider engaging a certified Caterpillar technician for proper diagnosis and repair, especially when working with critical electronic control systems.