What is Caterpillar Fault Code SPN 2335?

SPN 2335 indicates a malfunction in the Diesel Particulate Filter (DPF) Differential Pressure Sensor circuit. This sensor monitors the pressure difference across the DPF to determine the level of soot accumulation and trigger regeneration cycles when necessary.

This fault code specifically relates to the Electronic Control Module (ECM) detecting an abnormal voltage or signal from the differential pressure sensor that measures exhaust backpressure. On Caterpillar excavators equipped with Tier 4 emissions systems, this sensor is critical for aftertreatment system management. When the ECM cannot accurately read DPF restriction levels, it affects regeneration timing, fuel efficiency, and can ultimately lead to engine derate or shutdown to prevent catastrophic DPF damage. For used excavators, this code often signals sensor degradation, wiring issues from vibration exposure, or carbon buildup affecting sensor operation.

Common Symptoms

• Check Engine Light or malfunction indicator lamp illuminated on the instrument cluster
• Engine derate or reduced power output, particularly under load conditions
• Excessive exhaust smoke (black or white) due to improper regeneration cycles
• Frequent or failed regeneration attempts, with the regeneration indicator cycling abnormally
• Error messages on the monitor display specifically referencing aftertreatment or DPF system faults

Potential Causes

The most common technical reasons for SPN 2335 on used Caterpillar excavators include:

• Failed differential pressure sensor due to heat cycling, carbon contamination, or internal sensor element failure
• Damaged wiring harness or corroded connectors, especially at harness routing points near the exhaust system where heat and vibration cause insulation breakdown
• Blocked or kinked pressure sensing tubes connecting the sensor to the DPF inlet and outlet ports
• Carbon buildup inside the pressure sensing ports on the DPF canister itself, preventing accurate readings
• ECM calibration issues or software glitches requiring parameter updates
• Poor electrical ground connections at the sensor mounting location or ECM ground points

How to Troubleshoot and Fix Code SPN 2335

Step 1: Visual Inspection Begin with a thorough inspection of the differential pressure sensor location (typically mounted on the DPF housing). Check the electrical connector for corrosion, bent pins, or moisture intrusion. On used excavators, inspect the wiring harness for abrasion points where it contacts the frame or exhaust components—this is a frequent failure point.

Step 2: Pressure Line Verification Disconnect the two pressure sensing tubes (typically small rubber or silicone hoses) from the sensor. Blow compressed air through each tube to verify they're not blocked with carbon or soot. Inspect where these tubes connect to the DPF for carbon accumulation blocking the sensing ports.

Step 3: Electrical Testing Using a digital multimeter, check the supply voltage at the sensor connector (should typically be 5 volts reference from the ECM). Test sensor output voltage at idle and compare to manufacturer specifications (usually 0.5-4.5 volts depending on pressure). Check circuit resistance in the signal and ground wires back to the ECM—any reading above 5 ohms indicates wiring damage.

Step 4: Sensor Replacement and Calibration If electrical values are out of specification or pressure lines are clear but the code persists, replace the differential pressure sensor with a genuine Caterpillar part. After replacement, use Caterpillar Electronic Technician (CAT ET) diagnostic software to clear codes and perform a sensor calibration procedure. For used machines, this calibration step is essential as ECM adaptive parameters may need resetting.

Step 5: DPF Condition Assessment If the new sensor still triggers SPN 2335, the DPF itself may be excessively loaded or damaged. Perform a manual regeneration using diagnostic software and monitor pressure readings. Differential pressure exceeding 4-5 inches of mercury at rated speed indicates the DPF requires professional cleaning or replacement.

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Disclaimer: This guide provides general troubleshooting information. Always consult the official Caterpillar service manual for your specific model and serial number. Complex emissions system repairs should be performed by certified technicians with proper diagnostic equipment to ensure compliance with emissions regulations and warranty requirements.