I have a 2003 20th anniversary montero and i had a fault of P0155, which auto zone said its a bad heated 02 sensor, Bank 2, sensor 1. Where is that exactly on my truck? Please help, I have an emissions test due soon and I need to get it fixed before than.

 

it is under the car about middle, just about where the parking brake and gear shift are. the are 2 that are hard to get to while the other 2 are pretty easy.

 

Is the o2 sensor before or after the catalytic converter?

 

it is before, you will see them sticking out from the sides of the pipes once you go underneath. You cannot access them from the hood.

 

I found all 4 sensors before the catalytic converter, so which exactly is bank 2, sensor 1. I've googled it and I'm getting all kinds of different answers like before and after catalytic and drivers and passengers side, so I don't know who to believe. I went to auto zone who 1st told me what the fault code was for and they said its after the catalytic on the drivers side and the sensor cost $229. Dam that my Montero only has 51k miles, I thought that those sensors would last longer than that. Thanks again for any answers.

 

bank 2 on a montero is always the drivers side. sensor 1 is BEFORE the converter. beware, when you change that sensor the threads in the pipe may also come out, gotta take out the pipe and re tap the hole, or replace the pipe assembly.be careful

 

I did this one last year on my 03. Biggest pain in the A**.
Make sure you have an O2 sensor socket kit. I bought mine cheap at harbor freight tools.
My sensor was in there in such a way that it didn't come out straight and the threads were all mashed. I really had to wrench it out, so badly that I bent the sensor itself . I bought an O2 sensor thread chaser, it cleaned up the threads enough to make a tight seal. I never want to do that again....

 

I just bought a O2 sensor and it was only 65 dollars.

 

Let me guess. rendejesus22 must live in the great state of California. Why else would an O2 sensor be that much? Ouch!

As far as installation goes, I had one of those fancy O2 sensor sockets, but the sensor was so well stuck in there that the bottom of the socket just ended up slipping over the "teeth" of the sensor because all the torque is being applied at the other end. So, I used a liberal amount of penetrating oil, waited, and then used an old-fashioned adjustable wrench right where the bottom of the sensor is so I could use maximum force where it was needed most. A few taps with a rubber mallet and the rest was easy.

Not to say a sensor socket won't do the job — I've used them successfully before — but you can do just fine without one, too. Another little trick is to run your car for a minute or two so the pipe is warm to the touch but not hot. This will allow the metal to expand and can sometimes make it easier to reason with a stubborn sensor.

Good luck, and I hope you pass SMOG with no problems