P3839moderate severityPowertrain
DEF System Purge Valve Malfunction
on 2012 Audi Q7 3.0L TDI V6 · AWD
What this code means
The DEF system purge valve that drains DEF lines back to the tank during shutdown (to prevent freezing) has malfunctioned.
Symptoms
- DEF lines freeze in cold weather
- DEF system inoperative after cold soak
- Check Engine Light in cold conditions
- DEF pressure does not build on startup
- SCR system delayed activation in winter
Common causes
- Purge valve stuck open or closed
- Purge valve solenoid failure
- Wiring fault to purge valve
- Valve frozen in position
- Control circuit fault
Diagnostic steps
- Test purge valve operation at shutdown
- Command valve via scan tool
- Check valve solenoid resistance
- Inspect valve for ice or crystallization
- Monitor DEF line pressure during purge cycle
Repair notes
Replace DEF purge valve. Ensure DEF line heaters function to prevent future freeze damage.
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