Caterpillar Fault Code 586-9: Meaning, Symptoms, and Fix

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What is Caterpillar Fault Code 586-9?

Caterpillar Fault Code 586-9 indicates a loss of signal or abnormal update rate from the Transmission/Chassis ECM network communication circuit. Specifically, this code flags that the primary ECM is not receiving expected data from a secondary control module over the CAN (Controller Area Network) data link within the required time interval.

On Caterpillar machines, the CAN data link is the communication backbone connecting multiple control modules — including the engine, transmission, and implement controllers. When this network signal degrades or drops entirely, the machine's control systems cannot coordinate properly, directly impacting operational safety and performance.

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Common Symptoms

Operators and technicians may observe the following when Code 586-9 is active:

• Active fault lamp or MID warning illuminated on the operator display
• Intermittent or complete loss of machine response to transmission or implement commands
• Reduced power mode (derate) or unexpected machine shutdown
• Multiple secondary fault codes appearing simultaneously due to cascading ECM communication failures
• Erratic gauge readings or blank instrument cluster displays

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Potential Causes

The following are the most likely root causes, particularly on used or high-hour Caterpillar excavators:

• Damaged or corroded CAN data link wiring — common at harness flex points near the cab base or engine firewall
• Faulty or failing secondary ECM not transmitting data at the correct update rate
• Damaged 120-ohm terminating resistors at either end of the CAN bus circuit
• Loose, corroded, or water-intruded connectors at ECM pin locations (especially common in used machines with deferred maintenance)
• Battery voltage irregularities causing ECM communication dropouts during cranking or load spikes

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How to Troubleshoot and Fix Code 586-9

Step 1 — Connect Diagnostic Software Use Caterpillar ET (Electronic Technician) software to confirm the active fault, identify which module is failing to communicate, and check for any related codes. Document all active and logged faults before clearing.

Step 2 — Inspect the CAN Data Link Harness Physically trace the CAN High and CAN Low wires from ECM to ECM. On used excavators, pay close attention to harness rub points, zip-tie wear spots, and areas near hot engine components. Look for chafed insulation, corrosion, or broken conductors.

Step 3 — Check Terminating Resistors With the circuit de-energized, use a multimeter to measure resistance across the CAN bus. You should read approximately 60 ohms (two 120-ohm resistors in parallel). A reading significantly higher or lower indicates a failed terminating resistor or open/shorted circuit.

Step 4 — Inspect ECM Connectors Check all ECM connector pins for corrosion, bent terminals, or moisture intrusion. Apply Caterpillar electrical contact cleaner and dielectric grease after inspection.

Step 5 — Test or Replace the Suspect ECM If wiring and resistors test correctly, the secondary ECM may require reprogramming or replacement. Always verify correct flash file and parameter configuration after any ECM replacement using Cat ET.

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Disclaimer: This guide is intended for informational purposes for qualified heavy equipment mechanics and experienced operators. Always consult a certified Caterpillar dealer or licensed technician before performing ECM-level repairs. Improper diagnosis or repair can result in equipment damage, safety hazards, or voided warranties.