cobalt bung hole - what for?

trader · Postby **trader** » Wed Oct 23, 2013 10:45 am

My Cobalt exhaust came with a bung hole after the cat. Intrigued as to what that could be used for. I would have thought all sensors (wideband etc) would require fitment before the cat.

hks_kansei · Postby **hks_kansei** » Wed Oct 23, 2013 11:48 am

I seem to remember that California has/had different emissions laws than the rest of the US, and they required two sensors, one pre-cat, one post.

I think the reasoning was that if the cat has failed, the two sensors will match readings, and flash a warning light on the dash.

manga_blue · Postby **manga_blue** » Wed Oct 23, 2013 12:10 pm

Systems on most cars these days have an O2 sensor before and after the cat.

TieNN89 · Postby **TieNN89** » Wed Oct 23, 2013 9:59 pm

hks_kansei wrote:I seem to remember that California has/had different emissions laws than the rest of the US, and they required two sensors, one pre-cat, one post.

I think the reasoning was that if the cat has failed, the two sensors will match readings, and flash a warning light on the dash.

Correct

The NC has something like this

project.r.racing · Postby **project.r.racing** » Thu Oct 24, 2013 12:18 am

different markets also introduced tighter emissions controls in different periods. USA for example just on OBDII and tighter controlls in '95. took us up to 3 years later to have the same gear in various mazdas. so you'll find some usa made stuff in the mid 90s have extra bits and bobs.