What is Caterpillar Fault Code CID5847?

Caterpillar Fault Code CID5847 indicates an abnormal voltage condition detected in the machine's CAN (Controller Area Network) communication system, specifically related to improper termination resistance or a communication bus fault. This diagnostic trouble code (DTC) appears when the Electronic Control Module (ECM) detects that the CAN bus termination resistance falls outside the acceptable range of 55-65 ohms, signaling a breakdown in the communication network that connects various electronic controllers throughout the excavator.

This fault is critical because the CAN bus serves as the central nervous system for modern Caterpillar excavators, allowing the engine controller, hydraulic controller, display monitor, and other modules to exchange operational data. When CID5847 activates, communication disruptions can lead to degraded machine performance, inaccurate sensor readings, or complete system shutdowns.

Common Symptoms

• Warning lights illuminated on the instrument cluster, particularly the malfunction indicator lamp (MIL) or diagnostic lamp
• Intermittent loss of display functions or erratic gauge readings on the monitor panel
• Engine derate or reduced power output as the ECM enters a protective "limp mode"
• Multiple simultaneous fault codes appearing due to communication failures between controllers
• Inability to communicate with diagnostic software tools like Caterpillar Electronic Technician (Cat ET)

Potential Causes

The most common technical causes for CID5847 in used Caterpillar excavators include:

• Damaged or missing termination resistors at either end of the CAN bus network (typically 120-ohm resistors)
• Corroded or loose connector pins at the ECM, display panel, or junction points—especially common in machines exposed to moisture
• Wire harness chafing at known rub points near the swing bearing, boom cylinders, or engine compartment where movement causes insulation wear
• Failed electronic control module or communication module with internal circuit damage
• Aftermarket accessory installations that improperly tap into the CAN network without proper termination
• Voltage spikes from faulty alternators or battery issues damaging CAN transceivers in older machines

How to Troubleshoot and Fix Code CID5847

Step 1: Verify Termination Resistance Using a digital multimeter, disconnect power and measure resistance across the CAN High and CAN Low wires at the main ECM connector. You should read approximately 60 ohms with both termination resistors intact. A reading of 120 ohms indicates one missing terminator; infinite resistance means both are missing or the bus is severed.

Step 2: Inspect Physical Harness Condition On used excavators, thoroughly inspect the CAN bus harness for visible damage, particularly at flex points. Check all connectors for corrosion, bent pins, or moisture intrusion. Pay special attention to connectors near the cab floor, battery box, and hydraulic pump area where environmental exposure is highest.

Step 3: Isolate Faulty Module Disconnect controllers one at a time while monitoring resistance. When the faulty module is disconnected, resistance should return to normal specifications. Check wiring diagrams specific to your machine serial number to identify all CAN bus nodes.

Step 4: Test with Diagnostic Software Connect Cat ET or equivalent diagnostic software to verify communication with all modules. The software will identify which specific controller is not responding, narrowing down the fault location.

For used excavators, always inspect for previous repair attempts, spliced wires, or non-OEM components that may compromise the CAN network integrity before investing in expensive ECM replacements.

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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. Complex electrical diagnostics should be performed by qualified technicians with proper training and equipment.