What is Caterpillar Fault Code CID1720?

Caterpillar Fault Code CID1720 indicates a communication error or data link failure within the machine's CAN (Controller Area Network) bus system, specifically related to a module or component that has stopped responding or is sending invalid data to the Electronic Control Module (ECM). This diagnostic trouble code (DTC) signals that one or more electronic controllers on the excavator cannot properly communicate with the main ECM, disrupting the integrated control system that manages engine, hydraulic, and electrical functions.

This code is critical for Caterpillar excavators because modern machines rely on continuous data exchange between multiple electronic modules—including the engine controller, hydraulic controller, monitor display, and various sensors. When communication breaks down, the ECM cannot properly coordinate machine operations, potentially leading to performance limitations, safety system failures, or complete operational shutdown. For used excavators, this fault often stems from aging electrical infrastructure rather than catastrophic component failure.

Common Symptoms

• Warning lights illuminated on the operator display, often accompanied by "Check Engine" or specific communication error messages
• Machine enters derate mode or limp mode, limiting engine power and hydraulic function to protect systems
• Intermittent or complete loss of monitor display functions, including loss of operational data, backup camera, or gauge readings
• Erratic behavior of hydraulic systems, such as inconsistent boom/arm response or attachment control issues
• Engine may experience rough idling or unexpected shutdown in severe cases when critical communication is lost

Potential Causes

Damaged or corroded CAN bus wiring harness: On used excavators, harnesses frequently suffer from abrasion at routing points near the swing bearing, boom pivot, or undercarriage where repetitive movement causes wire chafing.

Failed electronic control module: The ECM itself or secondary controllers (hydraulic controller, display module) may have internal failures, particularly in high-hour machines exposed to vibration and heat cycles.

Loose or corroded electrical connectors: Moisture intrusion in Deutsch connectors or other multi-pin connections along the CAN network creates resistance or open circuits.

Faulty termination resistors: The CAN bus requires proper 120-ohm termination resistors at network endpoints; deterioration or disconnection disrupts the entire communication system.

Voltage supply issues: Inadequate battery voltage, failing alternators, or corroded ground connections prevent modules from maintaining stable communication protocols.

How to Troubleshoot and Fix Code CID1720

Step 1: Connect Diagnostic Software Use Caterpillar Electronic Technician (Cat ET) or compatible diagnostic software to read active and logged fault codes. Identify which specific module is failing to communicate—the software will typically indicate the source address or component name (e.g., "Hydraulic ECU," "Implement Controller"). Record all related codes and freeze frame data.

Step 2: Perform Visual Harness Inspection Focus on known wear points in used excavators: inspect the main wiring harness where it passes through the swing bearing area, along the boom, and near the engine firewall. Look for abraded insulation, pinched wires, or signs of rodent damage. Check all CAN bus connectors for bent pins, corrosion (green/white deposits), or moisture. Clean connectors with electrical contact cleaner and apply dielectric grease.

Step 3: Test CAN Bus Integrity Using a digital multimeter, measure resistance across the CAN-High and CAN-Low wires with all modules connected and ignition off—you should read approximately 60 ohms (two 120-ohm resistors in parallel). If readings are infinite or incorrect, locate and test termination resistors. Check for voltage presence on CAN lines with ignition on (typically 2.5V baseline with fluctuations during communication).

Step 4: Isolate the Faulty Module Systematically disconnect modules one at a time while monitoring with diagnostic software to identify which component causes communication restoration when removed. For used machines, prioritize testing display monitors and implement controllers as these frequently fail from environmental exposure.

Step 5: Verify Power and Ground Circuits Measure battery voltage at the suspected module connector (should be 12-14V with engine running). Test ground continuity from module chassis ground to battery negative—resistance should be less than 0.5 ohms. Poor grounds are extremely common in older excavators due to corrosion at frame mounting points.

Disclaimer: This guide provides general troubleshooting procedures for CID1720. Always consult the specific Caterpillar service manual for your excavator model and serial number. If you lack experience with electrical diagnostics or CAN bus systems, consult a certified Caterpillar technician to prevent further damage to electronic components.