P3837moderate severityPowertrain
DEF Injector Nozzle Crystallization Detected
on 2010 Audi Q7 3.0L TDI V6 · AWD
What this code means
The DEF injector nozzle has crystallized DEF deposits reducing spray quality and dosing accuracy.
Symptoms
- Check Engine Light
- White crystalline deposits visible near exhaust
- DEF dosing less effective
- SCR efficiency declining
- Increased NOx emissions
- Exhaust backpressure rising
Common causes
- Normal DEF crystallization over time
- Exhaust temperature too low during dosing
- DEF concentration incorrect
- Injector nozzle partially blocked
- Dosing occurring during low exhaust flow
Diagnostic steps
- Inspect DEF injector nozzle for crystallization
- Check exhaust temperature at injector location
- Test DEF quality with refractometer
- Monitor dosing quantity vs commanded
- Inspect decomposition tube condition
Repair notes
Remove and clean DEF injector nozzle. Replace decomposition tube if deposits are severe. Address low exhaust temperature cause.
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