When you're running Holland buses powered by the Cummins ISB 6.7L engine, the emissions aftertreatment system must work perfectly. One of the most critical—and least noticed—components is the DEF (Diesel Exhaust Fluid) head unit. If it fails or gives bad readings, it can trigger warning codes, reduced power modes, or non-compliance issues when you can’t afford them.
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Monitors DEF fluid level, temperature, and urea concentration and relays that accurate data back to your ECU
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Controls precise dosing of urea into the exhaust stream so the SCR (Selective Catalytic Reduction) system can lower NOx emissions effectively
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Built to match Holland / Cummins ISB 6.7L system requirements for compatibility and calibration fidelity
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Helps prevent fault codes, emissions warnings, and engine derates that arise from sensor drift or intermittent failures
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Designed to withstand vibration, thermal cycling, and contact with DEF chemistry
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Field-friendly replacement ensures minimal disruption to your fleet schedule
In bus operations, reliability is everything. A failing DEF head unit is often the hidden trigger behind many emissions problems. Installing the correct, OEM-matched unit restores accuracy to your system, protects your SCR function, and helps keep your buses running clean, compliant, and on the road.