When your Terex equipment runs a Cummins ISL engine, the DEF (Diesel Exhaust Fluid) head unit might be one of the least visible parts—but it’s one of the most critical. The Terex Cummins ISL DEF Head Unit (OEM 66901701) ensures your aftertreatment system knows exactly how much DEF is in the tank, what its temperature is, and how concentrated it is. A failing or inaccurate DEF head can lead to warning lights, emission faults, or engine derates just when you can’t afford them.
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Continuously measures DEF fluid level, temperature, and urea concentration and relays that information to the engine control module
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Controls precise dosing of urea into the exhaust stream, enabling the SCR (Selective Catalytic Reduction) system to reduce NOx reliably
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Designed to meet OEM 66901701 specifications, allowing for proper fit and calibration on Terex / Cummins ISL setups
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Helps prevent fault codes, emission warnings, and power derates that often arise from sensor drift or failure
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Built to withstand tough operating conditions—vibration, wide temperature swings, and exposure to DEF’s chemical properties
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Relatively easy to replace, minimizing downtime and restoring your emissions system integrity
If your equipment is showing DEF system errors or SCR faults, your DEF head is often the first place to look. Replacing it with the correct OEM 66901701 unit restores reliable feedback, protects your emissions chain, and ensures your machine stays compliant under all conditions. When emissions matter, this head unit is one component you can’t afford to ignore.




























































































































































































































































































