When your Thomas Bus equipped with a Cummins ISB 6.7L or B6.7 engine shows DEF (Diesel Exhaust Fluid) system warnings or derate conditions, the DEF head unit is often at the heart of the issue. This specialized component handles sensing and delivery functions for the DEF system, helping the engine manage emissions compliance and aftertreatment accuracy.
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Acts as the central module for DEF system operations: monitoring fluid level, temperature, and sometimes quality within the DEF tank, while coordinating with the dosing system.
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Interfaces with the engine control unit (ECU) to regulate when and how much DEF is injected into the exhaust stream, ensuring the Selective Catalytic Reduction (SCR) system can convert NOx effectively.
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Helps prevent fault codes and derate events by maintaining accurate data and proper flow control in the DEF circuit.
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Built to match Thomas Bus and Cummins specifications so it fits seamlessly into the existing system and communicates reliably with sensors and wiring.
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Because the head unit is exposed to harsh working conditions (temperature changes, DEF chemistry, vibration), replacing it with a genuine or quality-matched unit is vital to avoid frequent failure.
When a faulty DEF head unit causes system faults—like warning lights, limp mode, or erratic dosing—the best remedy is installing a proper replacement. In Thomas Bus applications, using an OEM-correct or quality remanufactured head ensures precise control of the DEF system, restores emissions compliance, and prevents future reliability issues. Trust Tamerx Diesel Parts to supply the correct head unit for your bus so your engine runs clean and confidently again.























































































































































































































































































