Caterpillar SPN 3367 Fault Code: Complete Diagnostic Guide

What is Caterpillar Fault Code SPN 3367?

SPN 3367 indicates a problem with the DEF (Diesel Exhaust Fluid) Tank Temperature Sensor circuit. This Suspect Parameter Number (SPN) is triggered when the Engine Control Module (ECM) detects an abnormal voltage reading from the temperature sensor monitoring the DEF tank, critical for proper Selective Catalytic Reduction (SCR) system operation.

This code directly affects your Caterpillar excavator's ability to manage exhaust emissions. The SCR system relies on accurate DEF temperature readings to control fluid injection rates. When SPN 3367 activates, the ECM cannot properly regulate DEF dosing, potentially leading to increased emissions, engine derating, and compliance failures. For used excavators operating in demanding environments, this sensor circuit is especially vulnerable to corrosion and temperature cycling damage.

Common Symptoms

When SPN 3367 is active, operators typically experience:

• Amber or red warning lights on the instrument cluster indicating emissions system malfunction
• Engine power derate (torque reduction) after a grace period, typically limiting machine to 50-75% power
• DEF quality warnings appearing on the display even with fresh fluid
• Poor cold-start performance when DEF tank temperatures aren't properly monitored
• Stored fault codes that may escalate to critical shutdown warnings if left unaddressed

Potential Causes

The most common technical reasons for SPN 3367 on used Caterpillar excavators include:

• DEF tank temperature sensor failure due to crystallization buildup or internal component degradation
• Wiring harness damage at known rub points near the DEF tank mounting bracket or chassis crossmembers
• Corroded electrical connectors exposed to road salt, DEF spills, or moisture intrusion
• ECM calibration issues following software updates or battery disconnection on older machines
• Poor ground connections at the chassis grounding point for the DEF system circuit
• Damaged sensor pins from improper connector insertion during previous repairs

How to Troubleshoot and Fix Code SPN 3367

Step 1: Visual Inspection Begin by inspecting the DEF tank temperature sensor connector for corrosion, bent pins, or DEF crystallization. On used excavators, check the wiring harness routing for chafing against frame rails or moving components. Clean connectors with electrical contact cleaner and verify the chassis ground strap is tight and corrosion-free.

Step 2: Electrical Testing Using a digital multimeter (DVOM), check sensor resistance with the connector disconnected. Most Caterpillar DEF temperature sensors show 1,800-2,200 ohms at 77°F. Check circuit voltage at the ECM connector—you should see approximately 5 volts reference voltage on the signal wire with ignition on, engine off.

Step 3: Advanced Diagnostics Connect Caterpillar Electronic Technician (ET) diagnostic software to monitor live sensor data. Compare DEF tank temperature readings against ambient temperature—variance beyond 15-20°F indicates sensor drift. For used machines, perform a wiggle test on harnesses while monitoring voltage to identify intermittent connections caused by harness wear.

Step 4: Component Replacement If sensor readings are out of specification or circuit voltage is incorrect, replace the DEF tank temperature sensor using OEM or quality aftermarket parts. Always apply dielectric grease to connector pins on used equipment to prevent future corrosion. Clear codes with ET software and perform a SCR system reset according to Caterpillar service procedures.

---

Disclaimer: This guide provides general diagnostic information for trained technicians. Always consult your Caterpillar service manual and follow proper safety procedures. For critical repairs or warranty concerns, contact an authorized Caterpillar dealer or certified heavy equipment mechanic.