What is Caterpillar Fault Code SPN1336?

SPN 1336 indicates a malfunction in the Diesel Particulate Filter (DPF) Intake Pressure Sensor circuit. This fault code triggers when the Engine Control Module (ECM) detects an abnormal voltage signal from the sensor that monitors exhaust backpressure before the DPF.

This sensor plays a critical role in Caterpillar's emissions control system by measuring differential pressure across the Diesel Particulate Filter. The ECM uses this data to determine when active or passive regeneration is needed to burn off accumulated soot. When SPN1336 is active, the machine cannot accurately assess DPF loading, potentially leading to incomplete regeneration cycles, reduced engine performance, or forced derate conditions. For used excavators, this code often signals wear-related issues in the exhaust aftertreatment system that require immediate attention to prevent costly DPF replacement.

Common Symptoms

• Engine derate or power reduction with amber or red warning lights illuminated on the dash
• Frequent or incomplete regeneration cycles that interrupt normal operation
• Check Engine light accompanied by high exhaust temperature warnings
• Poor throttle response or hesitation during acceleration under load
• Excessive black smoke from the exhaust during operation

Potential Causes

The most common technical causes for SPN1336 in used Caterpillar excavators include:

• Failed or contaminated DPF intake pressure sensor due to carbon buildup or internal sensor degradation
• Damaged wiring harness at known rub points near the turbocharger or exhaust manifold where heat and vibration cause insulation breakdown
• Corroded or loose electrical connectors at the sensor plug, especially on machines with high hours in wet or dusty environments
• Blocked or kinked pressure sensing lines (rubber hoses) connecting the sensor to exhaust measurement points
• ECM calibration issues or software glitches requiring updates, particularly on older machine software versions
• Shorted or open circuit conditions in the sensor's 5-volt reference or signal return wires

How to Troubleshoot and Fix Code SPN1336

Step 1: Visual Inspection Begin by locating the DPF intake pressure sensor on the exhaust system (typically mounted near the turbocharger outlet). Inspect all wiring harnesses for obvious damage, melting, or chafing against hot exhaust components. On used excavators, pay special attention to connector pins for corrosion or bent terminals. Check pressure sensing lines for cracks, blockages, or carbon buildup.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure resistance across sensor terminals (typically 1,000-3,000 ohms at room temperature). Check the 5-volt reference supply from the ECM at the harness connector—it should read 4.5-5.2 volts with key on, engine off. Test signal wire continuity and ground circuits for opens or shorts to ground.

Step 3: Sensor and Component Replacement If electrical tests pass, remove and inspect the sensor for carbon contamination. Clean pressure ports with appropriate solvent or compressed air. Replace the sensor if readings are out of specification. For persistent codes after sensor replacement, inspect the DPF substrate for excessive loading and check ECM software version using Caterpillar Electronic Technician (Cat ET). On high-hour used machines, harness replacement at wear points often resolves intermittent faults.

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Disclaimer: This guide provides general troubleshooting information. Always consult the official Caterpillar service manual for your specific machine model and consider engaging a certified technician for complex diagnostics and repairs.