What is Caterpillar Fault Code SPN1063?

SPN 1063 indicates a problem with the Aftertreatment #1 Diesel Exhaust Fluid (DEF) Tank Temperature sensor circuit. This Suspect Parameter Number specifically monitors the temperature of the DEF fluid stored in the tank, which is critical for proper Selective Catalytic Reduction (SCR) system operation.

This fault code appears when the Electronic Control Module (ECM) detects an abnormal voltage reading from the DEF tank temperature sensor, indicating the sensor is providing data outside expected parameters. For Caterpillar excavators equipped with advanced emissions systems (Tier 4 Final/Stage V), maintaining accurate DEF temperature monitoring is essential. The SCR system relies on this data to calculate proper DEF injection rates—if the temperature reading is incorrect, the system cannot optimize NOx reduction, potentially triggering engine derate or preventing the machine from starting.

Common Symptoms

• Check Engine Light or Amber Warning Lamp illuminated on the instrument cluster
• DEF system warning messages displayed on the monitor panel
• Engine power derate (reduced horsepower/torque) after a predetermined time period
• Engine may not start after shutdown if fault persists beyond programmed limits
• Abnormal DEF consumption or difficulty with DEF system regeneration cycles

Potential Causes

The most common technical reasons for SPN 1063 on used Caterpillar excavators include:

• DEF tank temperature sensor failure due to crystallized DEF contamination or internal sensor degradation
• Damaged or corroded wiring harness connections at the sensor connector—particularly common where harnesses route near frame rails or experience vibration
• Chafed wires at known rub points near the DEF tank mounting brackets
• Corroded pins in the sensor connector from DEF spillage during refilling operations
• ECM internal fault (less common) affecting the sensor circuit power supply or ground
• Poor ground connection at the chassis ground point for the DEF system circuit

How to Troubleshoot and Fix Code SPN1063

Step 1: Visual Inspection Begin with a thorough inspection of the DEF tank temperature sensor and its wiring harness. On used excavators, check for DEF crystallization around the sensor body and connector. Inspect the harness routing from the sensor to the main chassis harness for signs of rubbing, particularly where it passes mounting brackets or contacts metal edges.

Step 2: Connector and Continuity Testing Disconnect the sensor connector and inspect pins for corrosion or bent terminals. Using a digital multimeter, check for continuity between the sensor connector pins and the ECM connector (refer to Caterpillar wiring schematics for pin identification). Measure resistance through the harness—readings should typically be less than 5 ohms. Also verify ground circuit integrity.

Step 3: Sensor Resistance Testing With the sensor disconnected, measure resistance across the sensor terminals. Compare readings against Caterpillar specifications (typically 2,000-3,000 ohms at 68°F/20°C, varying with temperature). If resistance is out of specification or shows an open or short circuit, replace the sensor.

Step 4: Voltage Supply Check Using Caterpillar Electronic Technician (Cat ET) diagnostic software or a quality multimeter, verify the ECM is providing proper reference voltage (typically 5 volts) to the sensor circuit. Check signal wire voltage with key on, engine off.

Step 5: Address Used Equipment Considerations For used excavators, pay special attention to harness wear points and connector seal integrity. Clean any DEF residue with water, then apply dielectric grease to connector pins before reassembly. If replacing the sensor, inspect the DEF tank for contamination or crystallization that may have damaged the original sensor.

Disclaimer: This guide provides general troubleshooting information. Always consult the official Caterpillar service manual for your specific machine model and serial number. Complex electrical diagnostics should be performed by qualified technicians with proper diagnostic equipment and training.