What is Caterpillar Fault Code SPN1568?

SPN1568 indicates a problem with the Diesel Particulate Filter (DPF) Differential Pressure Sensor Circuit on Caterpillar equipment. This fault code specifically signals that the Electronic Control Module (ECM) has detected an abnormal voltage reading or electrical issue within the pressure sensor circuit that monitors exhaust backpressure across the DPF.

The DPF differential pressure sensor measures the pressure difference between the inlet and outlet of the diesel particulate filter. This data is critical for the ECM to determine when the DPF requires regeneration to burn off accumulated soot. On used Caterpillar excavators, this code directly affects emissions system performance and can trigger protective engine derating if left unresolved, potentially limiting machine productivity on the jobsite.

Common Symptoms

• Check Engine Light or Malfunction Indicator Lamp (MIL) illuminated on the instrument cluster
• Engine power derate or reduced performance mode activated to protect emissions components
• Frequent or unsuccessful DPF regeneration cycles, causing extended downtime
• Excessive black smoke from exhaust during operation
• Error messages displayed on the monitor indicating emissions system faults

Potential Causes

The most common technical causes for SPN1568 on used Caterpillar excavators include:

• Faulty DPF differential pressure sensor due to carbon buildup or internal sensor failure
• Damaged wiring harness or connector corrosion at the sensor connection point (common on machines with high hours)
• Broken or disconnected pressure hoses linking the sensor to the DPF measurement ports
• Clogged pressure sensing tubes from soot accumulation or debris intrusion
• ECM internal fault or software calibration issues (less common but possible on older machines)
• Physical damage to sensor mounting brackets causing misalignment or air leaks

How to Troubleshoot and Fix Code SPN1568

Step 1: Visual Inspection Begin by locating the DPF differential pressure sensor mounted near the diesel particulate filter assembly. Inspect all wiring harnesses for abrasion, pinching, or damage from rubbing against frame components—a common issue on used excavators. Check connector pins for corrosion, bent terminals, or moisture intrusion. Examine the pressure sensing tubes for cracks, disconnections, or blockages.

Step 2: Electrical Testing Using a digital multimeter, perform voltage and resistance checks on the sensor circuit. With ignition on and engine off, verify the sensor supply voltage (typically 5 volts) at the connector. Check circuit continuity between the sensor and ECM pins according to Caterpillar wiring diagrams. Resistance values should match factory specifications (usually 1-5k ohms depending on temperature).

Step 3: Sensor and Component Testing Disconnect the pressure hoses and inspect for carbon buildup or blockage—blow compressed air through the tubes carefully. If electrical tests pass, the sensor itself may have failed internally. On used excavators with high operating hours, sensor diaphragm fatigue is common. Replace the differential pressure sensor with a genuine Caterpillar part if testing confirms failure.

Step 4: Clear Code and Verify After repairs, use Caterpillar Electronic Technician (Cat ET) diagnostic software to clear fault codes and perform a stationary regeneration if needed. Monitor live data during operation to confirm proper pressure readings across various engine loads.

Disclaimer: This guide provides general troubleshooting information. Always consult official Caterpillar service manuals and consider professional diagnostic assistance for complex repairs, especially on emissions-critical systems.