Ammonia Slip Catalyst Efficiency Low
2009-2013 Audi A3 2.0L TDI
Description
The ammonia slip catalyst (ASC) downstream of the SCR is not effectively converting excess ammonia to nitrogen. Ammonia is escaping to atmosphere.
Symptoms
- Ammonia smell from exhaust
- Check Engine Light
- Failed emissions test
- Eye and throat irritation near exhaust
- White haze from tailpipe
Common Causes
- ASC catalyst degradation
- SCR over-dosing DEF causing excess ammonia
- ASC contamination
- Exhaust temperature too low for ASC
- ASC catalyst physically damaged
Diagnostic Steps
- Measure ammonia levels downstream of ASC
- Check DEF dosing rates for over-dosing
- Monitor SCR and ASC temperatures
- Inspect ASC for physical damage
- Test downstream NOx and NH3 sensors
Repair Notes
Replace ammonia slip catalyst. Correct any DEF over-dosing issue. Inspect SCR system calibration.
Related Codes
Other Powertrain Codes
- P0001Fuel Volume Regulator Control Circuit/Open
- P0002Fuel Volume Regulator Control Circuit Range/Performance
- P0003Fuel Volume Regulator Control Circuit Low
- P0004Fuel Volume Regulator Control Circuit High
- P0010Intake Camshaft Position Actuator Circuit/Open Bank 1
- P0011Intake Camshaft Position Timing Over-Advanced Bank 1
- P0012Intake Camshaft Position Timing Over-Retarded Bank 1
- P0013Exhaust Camshaft Position Actuator Circuit/Open Bank 1
- P0014Exhaust Camshaft Position Timing Over-Advanced Bank 1
- P0015Exhaust Camshaft Position Timing Over-Retarded Bank 1
P3891 on Other Vehicles
Common Questions
What does code P3891 mean on a 2009-2013 Audi A3?
P3891 stands for "Ammonia Slip Catalyst Efficiency Low". The ammonia slip catalyst (ASC) downstream of the SCR is not effectively converting excess ammonia to nitrogen. Ammonia is escaping to atmosphere.
What are the symptoms of P3891 on a Audi A3?
Common symptoms of P3891 include: Ammonia smell from exhaust, Check Engine Light, Failed emissions test, Eye and throat irritation near exhaust, White haze from tailpipe.
What causes P3891 on a 2009-2013 Audi A3?
Common causes of P3891 include: ASC catalyst degradation, SCR over-dosing DEF causing excess ammonia, ASC contamination, Exhaust temperature too low for ASC, ASC catalyst physically damaged.