When transporting students or passengers in a bus equipped with the Cummins ISB 6.7L engine, emission compliance isn’t a suggestion—it’s a necessity. One of the key components keeping your SCR (Selective Catalytic Reduction) system honest is the Blue Bird Cummins ISB 6.7L DEF Head Unit (OEM 5511561). If this module isn’t measuring or dosing correctly, you may get warning lights, derates, or emission faults when you least expect them.
-
Monitors DEF tank level, fluid temperature, and urea concentration, sending precise feedback to your vehicle’s ECU
-
Regulates the dosing of DEF into the exhaust stream to enable NOx reduction by the SCR system
-
Built to OEM 5511561 specifications for plug-in compatibility with Blue Bird / Cummins ISB systems
-
Helps prevent fault codes, emissions warnings, and engine derates caused by sensor drift or failures
-
Designed to withstand vibration, thermal cycling, and exposure to aggressive DEF chemistry
-
Field-friendly construction allows for quicker replacements and reduced downtime
In a bus operation, downtime is expensive—and a failing DEF head is a common culprit for emissions alarms. Installing the correct OEM 5511561 Blue Bird Cummins ISB 6.7L DEF Head Unit ensures your emission feedback loop remains solid, your SCR system works reliably, and your bus stays in compliance day after day. Don’t let a small sensor take your fleet out of service.