What is Caterpillar Fault Code 654-5?

Caterpillar Fault Code 654-5 indicates a "Hydraulic Main Relief Valve Solenoid - Current Below Normal or Open Circuit." This diagnostic trouble code (DTC) means the Electronic Control Module (ECM) has detected an electrical current flowing through the main relief valve solenoid that is lower than the manufacturer's specified range, or the circuit is completely open (broken).

This code affects the hydraulic system's pressure regulation, which is critical for maintaining proper implement control and preventing system damage. The main relief valve solenoid modulates hydraulic pressure based on ECM commands. When the circuit fails, the excavator cannot properly regulate maximum system pressure, potentially leading to reduced performance, erratic hydraulic function, or system protection modes that limit machine operation.

Common Symptoms

• Hydraulic system derate or reduced power – implements may move sluggishly or lack normal force
• Illuminated warning lamp on the instrument cluster, often accompanied by a fault code display
• Loss of fine control over boom, stick, or bucket movements due to improper pressure modulation
• Unexpected hydraulic noise or pressure spikes during operation
• Machine may enter limp mode, restricting certain functions to protect the hydraulic system from damage

Potential Causes

The most common technical causes for Code 654-5 on used Caterpillar excavators include:

• Open or damaged wiring harness – particularly at flex points near the main control valve where cables experience repeated bending and abrasion
• Corroded or loose electrical connectors at the solenoid or ECM, common in machines with high hours or exposure to moisture
• Failed main relief valve solenoid – internal coil breakage due to age, heat exposure, or electrical overstress
• Chafed wires rubbing against frame components, hydraulic lines, or cab mounting points
• ECM internal fault (less common) – damaged output driver circuit within the controller
• Poor ground connections in the chassis grounding system affecting circuit continuity

How to Troubleshoot and Fix Code 654-5

Step 1: Visual Inspection Perform a thorough inspection of the wiring harness from the ECM to the main relief valve solenoid. On used excavators, pay special attention to harness routing near articulation points, hydraulic valve banks, and the swing bearing area where wires commonly experience friction wear. Check all connectors for corrosion, bent pins, moisture intrusion, or loose connections.

Step 2: Electrical Testing Using a digital multimeter, disconnect the solenoid connector and measure resistance across the solenoid coil terminals. Compare readings to Caterpillar specifications (typically 3-8 ohms for most solenoids, but verify with your service manual). An infinite resistance reading indicates an open coil. Next, check for voltage supply at the harness connector with the ignition on – you should see battery voltage on the supply wire.

Step 3: Circuit Continuity and Ground Testing Test continuity from the ECM connector to the solenoid connector to identify breaks in the wiring. Check the ground circuit integrity, as poor grounds are frequently overlooked on older machines. Resistance to chassis ground should be less than 5 ohms. Use Caterpillar Electronic Technician (Cat ET) diagnostic software to perform active solenoid tests and monitor real-time current flow.

Step 4: Component Replacement and Verification If testing confirms solenoid failure, replace the main relief valve solenoid with a genuine Caterpillar or quality aftermarket part. For used excavators, always inspect and clean connector terminals before reassembly, applying dielectric grease to prevent future corrosion. Clear codes using Cat ET and perform a function test under load to verify proper operation.

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Disclaimer: This guide provides general troubleshooting information. Hydraulic and electrical systems can be dangerous. Always consult your Caterpillar service manual and consider professional diagnostic assistance for complex repairs, especially on used equipment with unknown service history.