Bank 1 refers to the downstream O2 sensor.

Here is some info.

 

which one you think i should fix first cat or o2.or which one most likely to be bad. thanks

 

This is what it said in the link I posted for you.

Test it if you can, if you can't then I'd just replace the cat.

 

thanks. will do

 

400 miles to the tank bad?!? Unless you got a massive tank thats damn good. When I had my neon I got about 500 km per tank which works out to about 28 or so mpg. Which combined city and highway is perfectly fine. You dont even want to know what I get in my truck

 

the problem was that i recently had my crank sensor replaced and the pcm had code 43 stored . for a few days i was getting very bad gas mileage. i would drive about 20 miles and use about half a quarter of a tank . so after i reset the pcm i noticed a little better gas mileage. my mother has the same year neon and when i drive her car i noticed her car has way better gas mileage . it was only after reseting the pcm on my car is when my car seemed to be getting gas mileage close to her car. also my car had this weird smell that made me suspect that the cat was bad or something . so the other night i was testing the car out when it started bucking and the next day i get this code 72

 

i have a question .someone posted that you should not use synthetic oil on high milage engines because it shrinks seals .and someone posted that you should use conventional oil because it swells seals .the question is if one swells and one shrinks then wouldnt synthetic blend be ideal oil .in other words wouldnt the seals be untouched because the two oils will cancel each other out

 

Synthetic blends are CRAP and not worth the extra money you spend. Synthetics, which are POE oils, used to shrink seals but new synthetics have special formulas to recondition seals. So you won't have the same problem.