What is Caterpillar Fault Code CID698?

Caterpillar Fault Code CID698 indicates a communication error with the Aftertreatment Device #1, specifically related to CAN (Controller Area Network) bus communication failures between the Engine Control Module (ECM) and the Diesel Exhaust Fluid (DEF) dosing system or Diesel Particulate Filter (DPF) components. This Component Identifier (CID) signals that the ECM cannot properly communicate with critical aftertreatment system components, which are essential for meeting emissions standards and maintaining optimal engine performance.

This fault is particularly critical on Caterpillar excavators because the aftertreatment system directly controls exhaust emissions, regeneration cycles, and overall engine efficiency. When communication fails, the machine may enter derate mode to protect the engine and prevent emissions violations. For used excavator owners, this code often appears due to age-related wiring deterioration, corrosion, or component failures common in machines with high operating hours.

Common Symptoms

• Check Engine Light or Malfunction Indicator Lamp (MIL) illuminated on the dashboard
• Engine derate or reduced power output, limiting machine productivity
• Frequent or incomplete DPF regenerations, causing excessive fuel consumption
• DEF system warnings or inability to detect proper DEF fluid levels
• Rough idle or hesitation during operation, particularly under load

Potential Causes

The most common technical reasons for CID698 on used Caterpillar excavators include:

• Damaged or corroded CAN bus wiring harness between the ECM and aftertreatment control module, especially at flex points near the engine mount or chassis frame
• Faulty Aftertreatment Control Unit (ACU) or Diesel Exhaust Fluid Doser module with internal communication failures
• Loose or corroded electrical connectors at the aftertreatment device, particularly the main harness connector
• ECM software issues or outdated calibration files requiring updates
• Physical damage to CAN bus termination resistors or short circuits in the communication network
• Water intrusion into connector pins causing intermittent communication loss, common in machines operating in wet conditions

How to Troubleshoot and Fix Code CID698

Step 1: Visual Inspection Begin with a thorough inspection of the wiring harness running from the ECM to the aftertreatment device. Check for obvious damage, chafing, or corrosion at connector pins. On used excavators, pay special attention to harness routing where cables contact the frame or pass through bulkheads—common rub points that cause wire damage over time.

Step 2: Check CAN Bus Communication Using Caterpillar Electronic Technician (Cat ET) diagnostic software or a compatible J1939 diagnostic tool, verify CAN bus voltage and communication integrity. Measure resistance between CAN High and CAN Low terminals; you should read approximately 60 ohms with the system powered off, indicating proper termination. Check for voltage fluctuations or signal dropouts that indicate intermittent connections.

Step 3: Test Aftertreatment Components Disconnect the Aftertreatment Control Unit connector and inspect for moisture, bent pins, or green corrosion—extremely common in older machines. Clean connections with electrical contact cleaner and apply dielectric grease. Use a multimeter to verify proper supply voltage (typically 12-24V depending on model) at the ACU connector with the key on.

Step 4: Component Replacement and Verification If wiring and connections test good, the ACU or DEF doser module may require replacement. Before purchasing new parts for used equipment, consider testing with a known-good component if available. After repairs, clear codes with Cat ET, perform a forced regeneration, and monitor for code recurrence during operation.

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Disclaimer: This guide provides general troubleshooting information. Always consult the official Caterpillar service manual for your specific machine model and serial number. If you're unfamiliar with electrical diagnostics or CAN bus systems, consult a certified Caterpillar technician to prevent further damage to electronic components.