Hi,

I have Galant 2004 ES/LS High. I thought that it was ES 4 door, but carfax is saying like that by VIN.

I have the check engine light on, and read the code, and showed several codes related to the o2 sensors.

I had the following code,

P0155 : 02S Heater CKT Malfunction 2/1 (bank 2 sensor 1 ?)

So, I changed the O2S to take care of it, but now it is creating more problem.

First, I am not sure if I changed the right one.
As you may be aware, when I open up the hood I see two sensors right away on the top, and two ones in the bottom.

I changed one top one on the right side when you see it from outside,
but had bunch of codes. I am assuming this is bank 2 sensor 1, and one
in the below will be bank 2 sensor 2.

Anyway, after replacing it, however, I even had some codes related
one on bank 2 sensor 2 too, so I thought I replaced wrong one.
To check it out, I unplugged the one which I think bank 2 sensor 2,
(I mean only the cable), and read the code again after unplugging battery
for a while and re-connecting it to reset the code, and driving until I have
the check engine light on.

Now, the code is like that,

1. P0154 - O2S Ckt No Activity Detected 2/1
2. P0151 - O2S Ckt Low Volts 2/1
3. P0155 - O2S Heater Ckt Malfunction 2/1
4. P0156 - O2S Ckt Malfunction 2/2
5. P0161 - O2S Heater Ckt malfunction 2/2

Now, I am confused more, even I am not sure if I replaced right one.
So, which one is the bank 2 sensor 1. Is it really the top right one I see right away when I open up the hood ? or the one in the bottom in the
right side.

The code P0154 seems to be from the fact that I unplugged the sensor
cable, then Bank 2 sensor 1 is one in the bottom not on the top ?

Give me some advice .... Please !!!