What is Caterpillar Fault Code SPN 1672?

SPN 1672 indicates an abnormal voltage condition detected in the Aftertreatment #1 Diesel Particulate Filter Differential Pressure Sensor circuit. This fault code specifically monitors the sensor responsible for measuring pressure differences across the diesel particulate filter (DPF), a critical component in Caterpillar's emissions control system.

The DPF differential pressure sensor provides real-time data to the Engine Control Module (ECM) about how restricted the DPF has become with accumulated soot. When the sensor circuit experiences voltage irregularities—whether too high, too low, or erratic—the ECM cannot accurately determine DPF loading status. This compromises the machine's ability to perform regeneration cycles properly, potentially leading to engine derate conditions or complete shutdown to prevent emissions system damage. For used excavators, this code is particularly critical because aging wiring harnesses and connector corrosion frequently cause false readings that trigger unnecessary component replacements.

Common Symptoms

• Check Engine Light (CEL) or Malfunction Indicator Lamp (MIL) illuminated on the operator display
• Engine derate resulting in reduced power output or limited maximum RPM (typically 25-50% power reduction)
• Frequent or continuous DPF regeneration requests even after successful regeneration cycles
• Error messages on the monitor screen indicating emissions system faults or sensor failures
• In severe cases, the machine may enter limp mode or refuse to start until the fault is addressed

Potential Causes

• Damaged or corroded wiring harness connections at the DPF differential pressure sensor (common on used machines with 5,000+ hours)
• Failed DPF differential pressure sensor due to heat exposure, vibration, or internal component degradation
• Chafed or pinched wiring along harness routing points near the exhaust system or frame rails
• ECM internal faults or corrupted calibration files (less common but possible in older machines)
• Poor electrical ground connections at sensor mounting points or chassis ground straps
• Water intrusion into connectors from pressure washing or environmental exposure
• DPF sensor hoses that are cracked, collapsed, or blocked with carbon deposits

How to Troubleshoot and Fix Code SPN 1672

Step 1: Perform Visual Inspection Begin by thoroughly inspecting the DPF differential pressure sensor and its associated wiring harness. The sensor is typically located on or near the DPF canister itself. Check for obvious physical damage, melted insulation from exhaust heat, or connector corrosion. On used excavators, pay special attention to harness routing where vibration or rubbing against metal surfaces commonly occurs. Inspect both rubber sensing hoses connected to the sensor for cracks, kinks, or carbon blockage.

Step 2: Test Electrical Circuit Integrity Using a digital multimeter, disconnect the sensor connector and measure resistance between the sensor terminals (typically should read 100-500 ohms depending on model—consult service manual for exact specifications). Check for continuity in the wiring harness from the sensor connector back to the ECM. Measure voltage supply at the sensor connector with the key on, engine off (should typically read 5 volts reference voltage from the ECM). Any significant deviation indicates harness damage or ECM issues.

Step 3: Clean Connections and Test Sensor Hoses Before replacing components, thoroughly clean all connector pins with electrical contact cleaner and apply dielectric grease to prevent future corrosion. Remove and inspect the sensor's pressure hoses—blow them out with compressed air to clear any carbon buildup. This is especially important on used machines where accumulated deposits can create false pressure readings.

Step 4: Diagnostic Software Analysis Connect Caterpillar Electronic Technician (Cat ET) or equivalent diagnostic software to monitor live sensor data. Observe the differential pressure readings at idle and under load. Compare readings against service manual specifications. The software can also identify intermittent faults and help determine if the issue is sensor-related or ECM-related.

Step 5: Component Replacement if Necessary If testing confirms sensor failure, replace the DPF differential pressure sensor with genuine Caterpillar or quality aftermarket parts. After replacement, clear fault codes using diagnostic software and perform a forced regeneration cycle to verify proper system operation. Always replace damaged harness sections rather than attempting temporary repairs on used equipment.

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Disclaimer: This guide provides general troubleshooting information for SPN 1672 on Caterpillar excavators. Always consult the specific service manual for your machine model and serial number. If you're unfamiliar with electrical diagnostics or emissions systems, consult a certified Caterpillar technician to prevent costly misdiagnosis or additional damage.