What is Caterpillar Fault Code CID1679?

Fault Code CID1679 indicates an abnormal frequency or voltage signal detected in the Engine Control Module (ECM) communication network, specifically related to the CAN (Controller Area Network) bus system. This diagnostic trouble code occurs when the ECM identifies irregular data transmission between critical electronic components within the Caterpillar machine's control system.

The CAN bus serves as the central nervous system for modern Caterpillar excavators, enabling real-time communication between the engine control module, hydraulic controllers, display monitors, and various sensors throughout the machine. When CID1679 triggers, it signals that message integrity has been compromised, potentially affecting multiple systems simultaneously. This is particularly critical in Caterpillar equipment because disrupted communication can cause the machine to enter derate mode or initiate unexpected shutdowns to protect engine and hydraulic components from operating with incomplete or corrupted data.

Common Symptoms

• Warning lights illuminated on the instrument cluster, particularly the malfunction indicator lamp (MIL) or check engine light
• Intermittent loss of gauge readings or display information on the monitor panel
• Engine derate condition where power output is automatically reduced to protect components
• Erratic hydraulic function response or delayed commands from joystick inputs
• Communication errors displayed on Cat Electronic Technician (ET) diagnostic software when attempting to connect

Potential Causes

The most frequent causes of CID1679 in used Caterpillar excavators include:

• Damaged CAN bus wiring harness due to abrasion against frame components or hydraulic lines—common wear points include routing near the swing bearing and boom cylinder areas
• Corroded or moisture-infiltrated connector pins at ECM or module junction points, especially on machines operating in marine or high-humidity environments
• Failed terminating resistors at either end of the CAN network (typically 120-ohm resistors)
• Faulty ECM internal communication circuits or processor issues in higher-hour machines
• Aftermarket accessory installations that improperly tap into the CAN network without proper isolation
• Voltage irregularities from aging battery cables or poor grounding connections affecting the entire electrical system

How to Troubleshoot and Fix Code CID1679

Step 1: Visual Inspection of Harness and Connectors Begin by thoroughly inspecting all wiring harnesses along the CAN bus network. On used excavators, focus on areas where harnesses route near moving components or sharp edges. Look for abraded insulation, pinched wires, or signs of harness repair tape. Disconnect and inspect all ECM connectors and module connections for corrosion, bent pins, or moisture intrusion—green corrosion is particularly common on machines over five years old.

Step 2: Measure CAN Bus Resistance Using a digital multimeter (DMM), disconnect power and measure resistance across the CAN-High and CAN-Low terminals at the ECM connector. You should read approximately 60 ohms with all modules connected (two 120-ohm terminating resistors in parallel). A reading significantly higher suggests an open circuit or failed terminating resistor; a lower reading indicates a short circuit condition.

Step 3: Test with Caterpillar ET Diagnostic Software Connect Cat Electronic Technician software to perform active diagnostics. Monitor live data while wiggling harness sections to identify intermittent connection failures. Check for additional communication-related codes that may pinpoint specific modules. For used excavators, verify all software flash files are current, as outdated ECM programming can sometimes cause communication errors.

Step 4: Voltage Supply Verification Measure supply voltage at the ECM power pins with the key on—should read battery voltage (typically 24-28V for Caterpillar equipment). Check ground circuits with a voltage drop test; any reading above 0.1V indicates excessive resistance requiring cleaning or replacement of ground connections.

Step 5: Component Isolation Testing If previous steps don't identify the issue, systematically disconnect non-essential modules (displays, auxiliary controllers) to isolate a potentially faulty component pulling down the network. This is especially important on used machines with aftermarket additions.

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Disclaimer: This guide provides general troubleshooting information for Caterpillar CID1679. Always consult the specific service manual for your excavator model and serial number. Complex electrical diagnostics should be performed by qualified technicians with proper Caterpillar diagnostic equipment. Improper repairs may cause additional system damage or void remaining warranty coverage.