16804/P0420/001056
From Ross-Tech Wiki
16804/P0420/001056 - Catalyst System; Bank 1: Efficiency Below Threshold
Possible Causes
- Oxygen Sensor(s) defective
- Oxygen Sensor(s) Control defective
Possible Solutions
- 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/zerothread?id=663057