I went to Advanced and had a OBD test to see what my check engine light was on my 99 civic D16Y8. The Code was

P0420
Catalyst Efficiency Below Threshold (bank 1)

Can anyone help me with this? I have no idea what this is and is for. Please PM me or email me at adva7328@yahoo.com

thanks for all the help everyone

 

Sounds like the CAT is probably clogged. I'd replace it. Try www.sohfast.com.

 

that is kinda what i thought because it is ideling low sometimes 2