What is Caterpillar Fault Code SPN568?

Fault Code SPN568 indicates a malfunction in the hydraulic system control circuit, specifically related to abnormal electrical signals from the main hydraulic pressure sensor or its associated wiring harness. This Suspect Parameter Number (SPN) is part of the J1939 diagnostic standard used across Caterpillar equipment and monitors the voltage/current feedback from sensors controlling hydraulic pressure delivery to the implement and travel systems.

On Caterpillar excavators, the Electronic Control Module (ECM) continuously monitors hydraulic pressure sensor readings to optimize performance and protect components. When SPN568 triggers, the ECM detects voltage readings outside the normal 0.5-4.5V range, signaling either an open circuit, short to ground, short to power, or sensor degradation. This fault is critical because hydraulic pressure regulation directly impacts boom speed, dipper force, swing torque, and overall machine productivity—making accurate sensor feedback essential for safe operation.

Common Symptoms

When SPN568 is active on your Caterpillar excavator, you may experience:

• Check Engine light or hydraulic system warning lamp illuminated on the instrument cluster
• Reduced hydraulic responsiveness or sluggish implement movement, particularly during heavy digging operations
• Engine derate mode engaged, limiting RPM to protect the drivetrain from hydraulic system irregularities
• Erratic hydraulic function—intermittent loss of power to boom, stick, or bucket cylinders
• Abnormal sounds from the hydraulic pump, such as cavitation or whining, indicating pressure control issues

Potential Causes

The most common technical causes for SPN568 on used Caterpillar excavators include:

• Faulty hydraulic pressure sensor—internal component failure due to age, contamination, or thermal cycling
• Damaged wiring harness—especially at known rub points near the main pump, swivel joint, or along the boom where vibration causes insulation wear
• Corroded or loose electrical connectors at the sensor or ECM interface, common in machines exposed to moisture or stored outdoors
• Short circuit to ground caused by pinched wires during previous maintenance or component replacement
• ECM internal fault—rare but possible in high-hour machines with electrical system history
• Contaminated hydraulic oil causing sensor membrane damage or erratic readings

How to Troubleshoot and Fix Code SPN568

Step 1: Visual Inspection Begin by powering down the machine and inspecting the main hydraulic pressure sensor (typically located on the main control valve or pump housing). Check for physical damage, oil leaks around the sensor body, and verify the electrical connector is fully seated with no corrosion on the pins. On used excavators, examine the entire wiring harness from sensor to ECM for chafing, particularly where it passes through metal brackets or near moving components.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure resistance across the sensor terminals—typical specification is 200-350 ohms at room temperature (consult your specific service manual). Next, check the supply voltage at the harness connector with ignition ON/engine OFF; you should see approximately 5 volts reference voltage from the ECM. Test for continuity between sensor ground and chassis ground, and verify no short-to-power condition exists.

Step 3: Advanced Diagnostics Connect Caterpillar Electronic Technician (Cat ET) diagnostic software to read live sensor data. Observe the pressure sensor voltage output while manually activating hydraulic functions—readings should change smoothly between 0.5V (low pressure) and 4.5V (high pressure). Erratic or frozen values confirm sensor failure. If sensor tests pass, perform a wiggle test on the harness while monitoring voltage to identify intermittent connections common in older machines.

Step 4: Component Replacement Replace the hydraulic pressure sensor using OEM or quality aftermarket parts with matching specifications. Apply dielectric grease to connector pins before reassembly to prevent future corrosion. If wiring damage is found, repair using heat-shrink solder connectors and reroute away from friction points—never use crimp connectors in critical sensor circuits. Clear codes with diagnostic software and perform a pressure calibration procedure per Caterpillar service guidelines.

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Disclaimer: This guide provides general troubleshooting information for SPN568. Hydraulic and electrical system diagnostics require proper training, specialized tools, and adherence to manufacturer safety procedures. Always consult a certified Caterpillar technician and your machine's specific service manual before performing repairs on used excavators.