What is Caterpillar Fault Code SPN 2268?

SPN 2268 indicates a malfunction in the Diesel Exhaust Fluid (DEF) Temperature Sensor 2 circuit. This Suspect Parameter Number specifically monitors the secondary temperature sensor that measures DEF fluid temperature in the Selective Catalytic Reduction (SCR) system on Caterpillar diesel engines equipped with emissions controls.

The Electronic Control Module (ECM) uses data from this sensor to regulate DEF injection rates and ensure proper SCR catalyst operation. When SPN 2268 triggers, the system detects voltage readings outside the expected range (typically 0.5-4.5 volts), indicating either sensor failure, wiring issues, or connector problems. This fault is critical because incorrect DEF temperature readings can cause improper dosing, leading to increased emissions, potential engine derate, and failure to meet EPA Tier 4 Final standards. On used excavators, this code often appears due to sensor degradation from thermal cycling and exposure to harsh environmental conditions.

Common Symptoms

• Amber or red warning light on the instrument cluster indicating DEF system malfunction
• Engine power derate (5-25% reduction) after a predetermined time period if fault persists
• DEF quality or level warnings appearing even when fluid is adequate
• Increased diesel exhaust visible due to improper SCR catalyst efficiency
• Stored fault codes in the ECM that may prevent machine from passing emissions inspections

Potential Causes

The most common technical causes for SPN 2268 on used Caterpillar excavators include:

• Failed DEF temperature sensor due to internal element degradation or contamination from crystallized urea
• Corroded or damaged wiring harness connections at the DEF tank or along the frame rail where harnesses experience vibration
• Connector pin corrosion caused by moisture intrusion in the DEF system electrical connectors
• Chafed wiring at known rub points near the DEF tank mounting brackets or chassis components
• ECM internal fault (less common) affecting the sensor supply voltage circuit
• Poor ground connections at the DEF system ground points on older machines

How to Troubleshoot and Fix Code SPN 2268

Step 1: Visual Inspection Begin with a thorough inspection of the DEF temperature sensor and associated wiring. Locate Temperature Sensor 2 (typically mounted on the DEF tank or supply line). Check for physical damage, corrosion on the connector pins, and evidence of DEF crystallization around the sensor body. On used excavators, pay special attention to harness routing near moving components or heat sources.

Step 2: Electrical Testing Using a digital multimeter, perform resistance and voltage checks. Disconnect the sensor connector and measure resistance across the sensor terminals (typical specification: 2,000-3,000 ohms at 68°F, decreasing with temperature). Check supply voltage from the ECM (should be approximately 5 volts). Inspect wiring continuity from sensor to ECM connector and verify ground circuit integrity (less than 5 ohms resistance).

Step 3: Advanced Diagnostics Connect Caterpillar Electronic Technician (Cat ET) diagnostic software to monitor live sensor data. Compare Temperature Sensor 2 readings with Sensor 1 and ambient temperature—discrepancies exceeding 15°F indicate sensor failure. Check for intermittent connections by wiggling harnesses while monitoring voltage. For used machines, remove and inspect connectors for green corrosion or bent pins that create intermittent contact.

Step 4: Component Replacement If testing confirms sensor failure, replace with a genuine Caterpillar DEF temperature sensor to ensure proper calibration. Clean connector terminals with electrical contact cleaner and apply dielectric grease. After replacement, clear codes with Cat ET and perform a stationary regeneration to verify proper system operation.

---

Disclaimer: This guide provides general troubleshooting information. Always consult the official Caterpillar service manual for your specific machine model and serial number. If unfamiliar with electrical diagnostics or emissions systems, seek assistance from a certified Caterpillar technician to avoid costly misdiagnosis or component damage.