What is Caterpillar 320C Fault Code 586?

Caterpillar 320C Fault Code 586 indicates a low voltage condition in the Fuel Rack Actuator (FRA) circuit, specifically detecting voltage below the expected threshold during engine operation. This diagnostic trouble code (DTC) is generated by the Electronic Control Module (ECM) when it detects insufficient voltage supply to the fuel injection system's rack actuator, which directly controls fuel delivery to the cylinders.

This fault is critical for the Cat 320C because the Fuel Rack Actuator is responsible for precise fuel metering in the mechanical unit injection (MEUI) system. When voltage drops below manufacturer specifications (typically below 10.5-11 volts during cranking or operation), the ECM cannot accurately control fuel delivery, leading to performance issues, potential engine shutdown, or failure to start. For used excavators, this code often points to electrical degradation rather than mechanical fuel system failure.

Common Symptoms

• Engine cranks but fails to start or starts with extreme difficulty, especially after the machine has been sitting
• Sudden engine stalling during operation, particularly under load or during hydraulic work cycles
• Check Engine light or warning lamp illuminated on the instrument cluster with reduced engine power
• Erratic engine RPM or rough idle, with the engine hunting for proper speed
• ECM may initiate derate mode, limiting engine power to 50-75% of normal output to protect components

Potential Causes

The most common technical causes for Code 586 on used Cat 320C excavators include:

• Weak or failing battery with insufficient voltage (below 12.4V at rest or below 10V during cranking)
• Corroded or loose battery cable connections at terminals, especially the ground connection to the frame
• Damaged wiring harness between the battery and ECM, particularly at known rub points near the engine mount and along the right-hand chassis rail
• Faulty alternator not maintaining proper charging voltage (should be 13.8-14.4V during operation)
• Poor ground connections at the ECM mounting bracket or engine block ground strap
• ECM power supply relay failure or blown fuses in the main power distribution circuit
• Internal ECM voltage regulator degradation (less common but possible in high-hour machines)

How to Troubleshoot and Fix Code 586

Step 1: Perform Initial Voltage Testing Using a digital multimeter (DMM), measure battery voltage with the engine off (should read 12.4-12.8V). Then check voltage during cranking—it should not drop below 10.5V. If voltage is low, load-test the battery and inspect battery cable connections for corrosion, particularly the negative ground cable. On used excavators, remove cables and clean terminals with a wire brush and apply dielectric grease.

Step 2: Inspect Wiring Harness and Connections Visually inspect the main power harness from the battery to the ECM, checking for chafing, cracking, or damage at known wear points (near swing bearing, along undercarriage frame rails). Pay special attention to connector pins at the ECM—corrosion or bent pins are common on machines with 5,000+ hours. Disconnect the ECM connector and inspect for green corrosion or moisture intrusion.

Step 3: Test Alternator Output and Ground Circuits With the engine running, measure alternator output at the battery terminals (should be 13.8-14.4V at 1,500 RPM). If voltage is low, test the alternator under load. Check ground resistance between the engine block and battery negative terminal—resistance should be less than 0.5 ohms. Clean and tighten the engine-to-frame ground strap, a frequently overlooked issue on older machines.

Step 4: Verify ECM Power Supply Using Caterpillar Electronic Technician (Cat ET) software or equivalent diagnostic tool, monitor real-time ECM supply voltage while cranking and during operation. Compare readings to factory specifications. Check the ECM power relay and associated fuses in the main fuse panel. For used excavators, consider that connector corrosion inside the cab's electrical panel is common after years of vibration and temperature cycling.

Step 5: Address Root Cause and Clear Code After repairs, clear the fault code using Cat ET software and perform a test run under load. Monitor for code recurrence. If voltage issues persist after addressing wiring and charging system problems, ECM replacement may be necessary, though this is rare for Code 586.

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Disclaimer: This guide provides general troubleshooting information for Caterpillar 320C excavators. Always consult the manufacturer's service manual and consider professional diagnostic services from a certified Cat technician, especially when working with electronic control systems. Improper diagnostics can lead to additional component damage or safety hazards.