The DEF injector, or dosing unit, sprays diesel exhaust fluid into the exhaust for the SCR system, and a clogged or failed one triggers emissions faults and derates.
What it does
The dosing unit meters DEF into the exhaust stream ahead of the SCR catalyst. Precise dosing is critical: too little and NOx is not reduced, too much and DEF crystallizes. The injector can clog with crystallized DEF or fail electrically.
Signs it is failing
- DEF dosing or reductant fault codes
- A countdown to a derate
- Crystallized DEF around the injector
- Incorrect DEF consumption
Replacement and what to know
A clogged injector can sometimes be cleaned of DEF crystals, but a failed unit is replaced. Using fresh, quality DEF reduces crystallization and clogging. Address dosing faults promptly, since they lead to derates.
Frequently asked questions
What does the DEF injector do?
It meters diesel exhaust fluid into the exhaust for the SCR system to reduce NOx.
Why does it clog?
DEF crystallizes when it dries, and poor-quality fluid worsens it, clogging the injector over time.
Can a bad DEF injector cause a derate?
Yes. Dosing faults trigger a countdown to reduced power, so address them promptly.
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