What is Caterpillar Fault Code SPN1679?

SPN 1679 indicates a problem with the Diesel Particulate Filter (DPF) Differential Pressure Sensor circuit or pressure reading is out of range. This sensor measures the pressure difference between the inlet and outlet of the DPF to determine exhaust backpressure and soot loading levels.

This fault code is part of the J1939 diagnostic protocol used across Caterpillar's electronic engine control systems. The DPF differential pressure sensor sends voltage signals to the Engine Control Module (ECM) to monitor filter restriction. When readings fall outside expected parameters—either too high, too low, or erratic—the ECM triggers SPN 1679. This is critical because improper DPF monitoring can prevent regeneration cycles, leading to engine derate, reduced power output, and potential costly DPF damage on used excavators where filter life may already be compromised.

Common Symptoms

• Check Engine Light or Amber Warning Lamp illuminated on the dash
• Engine derate mode activated, limiting machine to 50-75% power output
• High exhaust temperature warnings or frequent regeneration requests
• Black smoke from exhaust due to incomplete regeneration cycles
• Poor throttle response and reduced digging force during operation

Potential Causes

The most common technical causes for SPN 1679 on used Caterpillar excavators include:

• Failed or contaminated DPF differential pressure sensor (common after 5,000+ hours)
• Blocked or kinked pressure sensing lines connecting sensor to DPF housing
• Corroded or damaged wiring harness connectors at the sensor (especially in high-vibration mounting areas)
• Clogged DPF filter causing abnormally high pressure readings that exceed sensor range
• ECM calibration issues or outdated software requiring flash updates
• Broken or disconnected pressure hoses from DPF inlet/outlet ports due to heat degradation

How to Troubleshoot and Fix Code SPN1679

Step 1: Visual Inspection Begin with a thorough inspection of the DPF differential pressure sensor located near the DPF canister. Check all wiring harness connections for corrosion, bent pins, or oil contamination. On used excavators, inspect the pressure sensing lines (small rubber or nylon tubes) for cracks, kinks, or carbon buildup that can cause false readings.

Step 2: Electrical Testing Using a digital multimeter, check the sensor's power supply voltage (typically 5V reference from ECM) and ground circuit continuity. Measure sensor output voltage at idle and under load—it should range between 0.5-4.5V depending on DPF restriction. Compare readings with Caterpillar's Electronic Technician (ET) diagnostic software specifications for your specific engine model.

Step 3: Pressure Line and Sensor Testing Disconnect pressure sensing lines and blow compressed air through them to clear any soot or debris. If lines are clear but the code persists, perform a sensor bench test by applying known pressure values and verifying voltage output changes proportionally. Replace the sensor if readings are erratic or stuck.

Step 4: DPF Condition Assessment Check actual DPF soot loading using Cat ET software. If the filter shows excessive restriction (above 85% capacity), the sensor may be reading correctly, and the DPF requires professional cleaning or replacement—common on used machines with unknown maintenance history.

Disclaimer: This guide provides general troubleshooting information. Always consult Caterpillar service manuals and qualified diesel technicians for your specific machine model. Improper repairs can cause engine damage or void warranties.