16804/P0420/001056
From Ross-Tech Wiki
16804/P0420/001056 - Catalyst System; Bank 1: Efficiency Below Threshold
Possible Causes
- Leakage in Intake and/or Exhaust System
- Catalyst faulty
- Oxygen Sensor(s) faulty
- Oxygen Sensor(s) Control faulty
Possible Solutions
- Check Intake and Exhaust System for Leaks
- Check Catalyst
- Check Oxygen Sensor(s)
- Check Oxygen Sensor(s) Control
- Perform Oxygen Sensor(s) Aging Check
Special Notes
- For 1.8T's experiencing this fault code, this thread may be useful: http://forums.vwvortex.com/showthread.php?663057
- Check the Official Factory Repair Information for any TPI/TSBs that apply to dealer level Engine Controller flash updates for the vehicle in question.