What is Caterpillar Fault Code SPN1670?

SPN 1670 indicates a malfunction in the diesel particulate filter (DPF) differential pressure sensor circuit or an abnormal pressure reading across the DPF. This Suspect Parameter Number (SPN) specifically monitors the pressure differential between the inlet and outlet of the diesel particulate filter, which is critical for emissions control and engine protection on modern Caterpillar excavators.

The DPF differential pressure sensor measures back pressure to determine when the filter requires regeneration. When SPN 1670 triggers, the Electronic Control Module (ECM) has detected either an electrical fault in the sensor circuit or pressure readings outside acceptable parameters. This is critical because improper DPF monitoring can lead to incomplete regeneration cycles, excessive back pressure, engine derate, and potential DPF damage—especially problematic on used machines where filter loading history is unknown.

Common Symptoms

• Yellow warning light illuminated on the dash, often accompanied by a check engine indicator
• Engine derate or reduced power output, particularly during heavy digging operations
• Frequent or failed regeneration attempts, with the operator noticing extended high-idle periods
• Excessive black smoke during acceleration if the DPF is physically clogged and regeneration cannot complete
• Poor fuel economy due to the ECM attempting compensatory fuel strategies

Potential Causes

The most common technical causes for SPN 1670 on used Caterpillar excavators include:

• Faulty DPF differential pressure sensor due to carbon buildup, heat damage, or internal component failure
• Damaged or corroded wiring harness at connection points, particularly where the harness routes near hot exhaust components or rubs against frame members
• Clogged pressure sensing lines leading to the sensor, often from carbon deposits or ash accumulation
• Physically loaded or damaged DPF causing actual excessive back pressure beyond sensor fault
• ECM software issues or calibration errors, more common after previous repairs or ECM replacements on used equipment
• Poor electrical connections at the sensor connector due to corrosion from moisture intrusion in older machines

How to Troubleshoot and Fix Code SPN1670

Step 1: Connect Diagnostic Software Use Caterpillar Electronic Technician (Cat ET) or equivalent diagnostic software to read active and stored codes. Check freeze frame data to determine if the fault is electrical (circuit voltage) or operational (pressure reading out of range).

Step 2: Inspect Sensor and Wiring Locate the DPF differential pressure sensor on the exhaust system. Visually inspect the sensor body for heat damage, cracks, or carbon accumulation. Thoroughly examine the wiring harness for chafing, particularly at mounting brackets and where it passes near moving components. On used excavators, check connector pins for corrosion or bent terminals—clean with electrical contact cleaner if needed.

Step 3: Test Electrical Circuit Disconnect the sensor and use a digital multimeter to check supply voltage (typically 5V reference) and ground continuity at the harness side. Measure sensor resistance according to Caterpillar specifications (consult service manual for exact values). Replace sensor if readings are out of specification.

Step 4: Check Pressure Sensing Lines Inspect rubber or metal sensing lines connecting the DPF to the sensor for cracks, kinks, or blockages. Remove and clean lines if carbon buildup is suspected. This is especially important on used machines with unknown maintenance history.

Step 5: Verify DPF Condition If electrical tests pass, perform a manual regeneration using Cat ET and monitor actual pressure values. Excessive back pressure may indicate a physically clogged DPF requiring professional cleaning or replacement.

Disclaimer: This guide provides general troubleshooting information. Always consult the official Caterpillar service manual for your specific machine model and serial number. Complex diagnostics and DPF system repairs should be performed by qualified diesel technicians with proper equipment and safety protocols.