What is Case CX220C Fault Code 601?

Case CX220C Fault Code 601 indicates a hydraulic pump solenoid circuit malfunction, specifically a detected open circuit or short in the main pump control solenoid wiring. This diagnostic trouble code (DTC) is generated by the Electronic Control Module (ECM) when it cannot properly regulate hydraulic pump output due to electrical communication failure with the pump's proportional control solenoid.

This code is critical for the CX220C because the hydraulic pump solenoid directly controls pump displacement and flow rate. When this circuit fails, the excavator cannot properly modulate hydraulic power, resulting in either reduced performance or complete loss of hydraulic functions. The ECM continuously monitors solenoid resistance and voltage feedback; any reading outside the 2-5 ohm resistance range or improper voltage response triggers Code 601.

Common Symptoms

• Complete loss of hydraulic power to boom, stick, bucket, and swing functions while engine continues running normally
• Illuminated warning lamp on the instrument cluster with possible audible alarm
• Erratic or sluggish hydraulic response during initial operation before complete failure
• Engine operates normally but implements do not respond to joystick/pilot control inputs
• Intermittent functionality that worsens with machine vibration or temperature changes

Potential Causes

The most common causes of Code 601 on used CX220C excavators include:

• Damaged wiring harness between the ECM and hydraulic pump, particularly where the harness routes near the pump mounting bracket (known rub point on this model)
• Corroded or loose connector pins at the pump solenoid connector, especially on machines with high hour counts or exposure to moisture
• Failed proportional solenoid within the hydraulic pump assembly due to internal coil breakdown or mechanical wear
• ECM internal driver circuit failure, though less common than external wiring issues
• Chafed insulation on solenoid wires from contact with sharp edges or rotating components near the pump

How to Troubleshoot and Fix Code 601

Step 1: Visual Inspection Begin by inspecting the wiring harness from the ECM to the hydraulic pump solenoid. On used excavators, check specifically where the harness passes along the left side of the engine near the pump mounting area—this is a known wear point. Look for abraded insulation, pinched wires, or signs of previous repairs. Inspect the solenoid connector for corrosion, bent pins, or moisture intrusion.

Step 2: Electrical Testing Disconnect the solenoid connector at the pump. Using a digital multimeter, measure resistance across the solenoid terminals—specification is 2-5 ohms at room temperature. Next, check for short to ground by measuring resistance between each solenoid terminal and machine ground (should read open circuit/infinite resistance). Inspect harness continuity from the ECM connector to the pump-side connector; any reading above 0.5 ohms indicates damaged wiring.

Step 3: Power and Ground Verification With the key on and engine off, verify the ECM is supplying proper voltage to the solenoid circuit (typically 12V reference). Check the ground circuit integrity, as corroded ground connections are common on older machines. Use Case diagnostic software (ServiceMaster or equivalent) to command the solenoid while monitoring actual versus commanded values.

Step 4: Component Replacement If wiring and connections test satisfactorily, replace the pump solenoid. On used excavators with over 6,000 hours, consider replacing the entire harness section if any wire damage is found, as adjacent wires often fail shortly after. After repairs, clear codes and perform a functional test under load.

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Disclaimer: This guide provides general troubleshooting information. Always consult the official Case service manual for your specific serial number and consider professional diagnosis for complex electrical issues or if you lack proper diagnostic equipment.