P3837moderate severityPowertrain
DEF Injector Nozzle Crystallization Detected
on 2014 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.
Other Powertrain codes on this vehicle
P0001
Fuel Volume Regulator Control Circuit/Open
P0002
Fuel Volume Regulator Control Circuit Range/Performance
P0003
Fuel Volume Regulator Control Circuit Low
P0004
Fuel Volume Regulator Control Circuit High
P0010
Intake Camshaft Position Actuator Circuit/Open Bank 1
P0011
Intake Camshaft Position Timing Over-Advanced Bank 1
P0012
Intake Camshaft Position Timing Over-Retarded Bank 1
P0013
Exhaust Camshaft Position Actuator Circuit/Open Bank 1
P0014
Exhaust Camshaft Position Timing Over-Advanced Bank 1
P0015
Exhaust Camshaft Position Timing Over-Retarded Bank 1