What is Caterpillar Fault Code SPN1373?

SPN 1373 indicates a problem with the Engine Turbocharger 1 Wastegate Actuator Control Circuit or the wastegate actuator itself. This Suspect Parameter Number (SPN) is part of the J1939 diagnostic protocol used across Caterpillar engines and signals that the Electronic Control Module (ECM) has detected an electrical fault or performance issue with the turbocharger wastegate control system.

The wastegate actuator regulates boost pressure by controlling exhaust gas flow around the turbine wheel. When SPN 1373 triggers, the ECM cannot properly modulate turbo boost, which directly impacts engine performance, fuel efficiency, and emission control. For used Caterpillar excavators, this code often appears due to age-related electrical degradation or mechanical wear in the turbocharger system, making timely diagnosis critical to prevent further engine damage or derate conditions.

Common Symptoms

• Check Engine Light or amber warning lamp illuminated on the instrument cluster
• Engine power loss or derate, especially noticeable during heavy digging or lifting operations
• Excessive black or gray exhaust smoke indicating improper air-fuel mixture due to boost control failure
• Turbocharger overboosting or underboosting, causing rough engine operation or unusual turbo whistle sounds
• Reduced hydraulic system performance as engine power output becomes inconsistent

Potential Causes

The most common technical causes for SPN 1373 in used Caterpillar excavators include:

• Faulty wastegate actuator solenoid with internal coil failure or sticking valve
• Damaged or corroded wiring harness at the turbocharger connection point, particularly where the harness routes near hot exhaust components
• Open or short circuit in the wastegate actuator control wiring between the ECM and actuator
• Failed wastegate actuator position sensor preventing proper feedback to the ECM
• Contaminated electrical connectors due to oil seepage, coolant intrusion, or environmental exposure common in older machines
• ECM internal driver circuit failure, though less common than external component issues

How to Troubleshoot and Fix Code SPN1373

Step 1: Visual Inspection Begin by thoroughly inspecting the wastegate actuator wiring harness from the turbocharger to the ECM connector. On used excavators, check for obvious damage such as wire chafing against the engine block, melted insulation near exhaust manifolds, or corroded connectors. Clean all electrical connections with electrical contact cleaner and apply dielectric grease.

Step 2: Electrical Testing Using a digital multimeter (DMM), check the wastegate actuator solenoid resistance. Typical specifications range from 10-30 ohms depending on the specific turbocharger model—consult your service manual. Disconnect the actuator connector and measure resistance across the solenoid terminals. Also check for short to ground by measuring resistance between each terminal and the engine block (should read infinite resistance).

Step 3: Actuator Function Test With Caterpillar Electronic Technician (Cat ET) diagnostic software connected, perform an actuator output test to verify the ECM can command the wastegate. Listen for audible clicking from the solenoid and observe boost pressure response. If the ECM commands properly but the actuator doesn't respond, replace the wastegate actuator assembly.

Step 4: Advanced Diagnostics If wiring and actuator test good, inspect the wastegate linkage for mechanical binding or carbon buildup preventing movement. On high-hour used machines, the wastegate arm can seize due to exhaust deposits. Additionally, verify supply voltage from the ECM (typically 12V switched) reaches the actuator connector during operation.

Critical Note for Used Equipment: Before replacing expensive components, thoroughly investigate harness routing and connector condition, as these are the most common failure points in aging excavators. Previous repairs may have created new rub points or inadequate strain relief.

---

Disclaimer: This guide provides general troubleshooting information. Always consult the official Caterpillar service manual for your specific engine model and serial number. If you lack proper diagnostic tools or experience with high-pressure turbocharger systems, consult a certified Caterpillar technician to prevent injury or further equipment damage.