Thomas Bus Detroit DD5, DD8 DEF Head Unit

DEF Accuracy Restored for Thomas Bus — OEM DEF Head Unit (04‑33656‑000), 2021–2024

What is it?
The OEM 04‑33656‑000 DEF Head Unit is a factory-grade header assembly used in Thomas Built Buses powered by Detroit DD5 or DD8 engines (model years 2021–2024). It sits on top of the DEF tank and includes sensors that monitor fluid level, temperature, and enable proper SCR system control to ensure compliance with emissions standards.

Why choose this OEM DEF Head Unit?
Crafted to Detroit’s original specifications, this component ensures the correct sensor calibration, precise sealing, and plug-and-play compatibility with the vehicle’s electronic control systems. Choosing the genuine part helps prevent common issues like false warnings, sensor faults, fluid leaks, or SCR performance disruptions associated with non‑OEM units.

Key Benefits
 ✅ Direct OEM fit for Thomas buses with Detroit DD5 / DD8 (2021–2024)
 ✅ Accurate sensing of DEF fluid level and temperature
 ✅ Sealed design to prevent leaks and protect system integrity
 ✅ Supports factory diagnostics and seamless SCR integration
 ✅ Built for durability under heavy vehicle operation

Applications
Ideal for Thomas transit, school, or shuttle buses using Detroit DD5 or DD8 engines fitted with SCR systems. The head unit is essential for maintaining emissions compliance and stable DEF system performance across daily driving, route operations, and fleet service.

Installation Notes
Install by a qualified technician. First, depressurize or disable the DEF system. Clean the mounting surfaces and inspect for seal damage. Replace any worn O‑rings or gaskets. Mount the head unit with the correct torque values. After installation, verify sensor readings, confirm proper system function, and clear any DEF or SCR fault codes through diagnostics.

Final Thoughts
If your Thomas bus is giving DEF-level warnings, erratic sensor readings, or DEF system faults, the OEM 04‑33656‑000 DEF Head Unit is the solution. Restoring real, factory-level accuracy and reliability, it helps keep your bus emissions‑compliant and running smoothly.