Hi all, new guy here. The 05 Ion 3 I bought for my daughter is throwing a P0420 code, catalys system under efficiency threshold. Figured before I get myself into a new cat situation on a thousand dollar car, I'd go over the basics and see if its throwing this code for other reasons. It idels rough and has stalled a couple times, restarted immediately, so I just did new plugs and a coil module while I was doing the oil, idle seems to be nice and smooth now and it definitely feels a bit more powerful to the butt dyno.

Next step is the front O2 sensor, which is relatively inexpensive. Might have found the issue though...the front O2 sensor seems to be missing from the car. If I look down the back of the engine bay, basically the exhaust manifold goes right down to the cat (or front cat I assume), right? There is a bung off to the driver's side on the manifold pipe and its got a bolt in it. Not a sensor, not part of a sensor...its just a bolt. Am I correct in this is where the front sensor is supposed to be and I've got something weird going on here or am I just looking in the wrong place? If the sensor is actually missing, can anyone explain why I was able to get an inspection sticker and why the car has been driven thousands of miles without a check engine light coming on? Is there a delete kit or something that I'm going to havbe to undo? Where should I be looking for the empty O2 sensor plug under the hood? I think its near the trans maybe?

Thanks in advance!

 

I bought an 02 Olds Alero with a 2.2 and it had an exhaust header on it. No codes but it also had no front oxygen sensor. Don’t know how but maybe the car just ignores the lack of input and does a work around.

 

My last ion ran with both sensors undone for performance reasons.
but if youre trying to get the car right, a sensor is cheap. Just get a quality one.
from there it'll tell you if you'll need a cat or not.

Also clean the maf with maf cleaner and clean the throttle body also.make sure the air filter is good as well