2007 Optima v6 - Check Engine

[courtroom74]

Hi all,

07 optima v6 EX 86K.
Some back ground info first. For the pass 9 months , I get the Check Engine light DTC 300 - missed fired, no specific cylinder - on and off in several occasions. Try to locate the exact problem but didn't see anything. Checked wire, spark plugs etc. and reset light. It will come back randomly later. Some times comes back in few months, some time in few weeks.

Just got a Check Engine light again last week, this time DTC indicated p0430 @ Bank 2, (different from before) code indicates it would be several possible issues. Reset the light and see if the problem repeats, it came back after few days.

After research a bit on the net, many suggested to check and replace O2 sensor before replace cat converter (expensive). I looked into the location of the sensors this weekend, this is what I saw and I have a few questions.
(1) I saw a sensor at the front and back of the engine block, the front is easy to get to, but the back is not (at least from what I can observe).
(a) Is Bank 1 referred to the front (cylinder 1) and Bank 2 is the back?
(b) Are the sensors I saw (under the hood) considered the "pre" cat sensors?

(2) I saw two sensors underneath the car. One is on the left side and the other on the right.
(a) Are these the "post" cat sensors? Which side is Bank 1 and Bank 2?
(b) I didn't see where the wires are connected to, I'll need to disconnect them before I can replace it, anyone know where they maybe?

(3) Anyone has this same issue? Does it make sense for me to try and replace the "post" cat sensors before replacing cat?

(4) I wonder if the root cause maybe linked to the previous code in the pass 9 months (300)? If it is, even replacing cat may not resolve the issue?

Suggestion and recommendation are welcome. Thanks in advance.

[Crvett69]

bank 1 sensor 1 and bank 2 sensor 1 are the ones closest to the engine. bank 1 would be the side that plug #1 is on. sensor 1-2 and 2-2 would be the rearward ones past the converters. i would suggest replacing both rearward ones at the same time if you getting codes. if codes come back after that you may have bad convertors

[courtroom74]

Thank you for the clarification on banks and sensors. Now I need to locate the connectors, I didn't see them last time when I got under the car. I hope it will be in a spot that's accessible.