What is Caterpillar Fault Code SPN 1585?

SPN 1585 indicates a Turbocharger Wastegate Actuator Control Circuit malfunction in Caterpillar excavators and heavy equipment. This Suspect Parameter Number (SPN) signals that the Electronic Control Module (ECM) has detected an electrical issue with the circuit controlling the turbocharger's wastegate actuator, preventing proper boost pressure regulation.

The wastegate actuator controls exhaust gas flow around the turbine wheel, directly regulating turbocharger boost pressure. When SPN 1585 triggers, the ECM cannot properly command the wastegate position, compromising engine power output and fuel efficiency. For used Caterpillar excavators, this code is critical because improper boost control can lead to over-boosting, under-boosting, or engine derating to prevent catastrophic damage to the turbocharger or engine internals.

Common Symptoms

• Engine derate or reduced power mode activated, limiting machine performance to 50-75% capacity
• Check Engine Light or Diagnostic Warning Lamp illuminated on the instrument cluster
• Excessive black smoke from exhaust during acceleration due to improper air-fuel ratio
• Poor throttle response or sluggish acceleration under load
• Turbocharger over-boost or under-boost conditions detected during operation

Potential Causes

The most common technical causes for SPN 1585 in used Caterpillar excavators include:

• Wastegate actuator solenoid failure due to internal coil breakdown or mechanical binding from carbon buildup
• Wiring harness damage at known rub points near the turbocharger heat shield or engine block
• Corroded or loose electrical connectors on the wastegate actuator circuit, especially on machines with high operating hours
• ECM internal driver circuit failure preventing proper actuator signal output
• Open or short circuits in the harness between the ECM and wastegate actuator
• Failed wastegate position sensor providing incorrect feedback to the ECM

How to Troubleshoot and Fix Code SPN 1585

Step 1: Perform Visual Inspection Begin by inspecting the wiring harness from the ECM to the turbocharger wastegate actuator. On used excavators, check for harness chafing against the engine block, heat damage near exhaust components, and connector corrosion. Clean all connectors with electrical contact cleaner and verify secure connections.

Step 2: Test Wastegate Actuator Resistance Disconnect the wastegate actuator connector and use a digital multimeter to measure solenoid resistance. Typical specifications range from 10-30 ohms (consult your specific model's service manual). Readings outside this range indicate actuator replacement is necessary.

Step 3: Check Circuit Continuity and Voltage With Caterpillar Electronic Technician (Cat ET) software connected, perform actuator output tests while monitoring voltage at the actuator connector. You should see battery voltage (approximately 12-14V) when commanded. Check for open circuits or shorts to ground using the multimeter's continuity function on each wire.

Step 4: Inspect Mechanical Wastegate Operation Manually verify the wastegate linkage moves freely without binding. Carbon buildup and corrosion commonly restrict movement on high-hour machines, preventing electrical signals from translating to mechanical action.

Step 5: Clear Code and Perform Operational Test After repairs, clear fault codes using Cat ET and perform a loaded operational test, monitoring boost pressure parameters to confirm proper wastegate control.

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Disclaimer: This guide provides general troubleshooting information for SPN 1585. Always consult your specific Caterpillar service manual and consider professional diagnostic services for complex electrical issues or if you lack proper diagnostic tools.