Does anyone know what a P2251 code is? I think it's one of the O2 sensor but don't know which one. Also does anyone have any diagrams or instructions on replacing the O2 sensors on a 2004 TL? I've searched various forums and google but it seems that I might be the first one with a P2251 code on a TL. Thanks in advance.

 

its the top sensor in the rear. bank one sensor one. a/f sensor. now its possable there a short in the harness. i would check to make sure a rat didn't get back there a chew it up.

 

You don't happen to have a diagram or know where I can find the location of the sensor do you? Do you know how much it would cost to fix it at a dealer since it looks like you work for one from your sig.

 

I'm having the same code and P0134 also. The P2251 is a rear A/F sensor 11 VS line high voltage and the P0134 is A/F sensor 1 heater system malfunction. I have no clue what is the problem, if somebody know what it is please let me know. Thanks in advance.

 

Its about 250 and 150 installed. Take the cover of under the hood in the back.
Pass the valve cover you will see it sticking strait up. Trust me you can do it urself.

 

240sx, Thanks for the info. I have just one last question to ask you, do you know the correct part number? I ask my local dealer and said it's the top rear sensor on bank 1 sensor 1 and they said which one. Thanks again.

 

flouie did you change your sensor? Was that the problem? Im getting these same codes.

 

I am getting both of these codes as well. Flouie or Joe2006TL were you able to fix these without taking them to the dealership. Someone please help...I don't have money to pay the dealership right now

 

hello, i am getting both of these p0134 and p2251 error codes, how do i know where each part is located and which part # it is?

cheers,
daniel

 

I installed the rear upstream O2 sensor (P2251) last year - the DIY writeup is below:

https://acurazine.com/forums/3g-tl-problems-fixes-114/e-130-diy-oxygen-o2-sensor-installation-rear-upstream-f-aka-p2251-811823/

 

just got p2251 on my 05 rl. Anybody have a solution for this?

 

These codes were getting thrown by my wife's 2005 Acura MDX. As this thread has explained and as further research shows, these codes refer to Bank 1, Sensor 1. A better description of this is the upstream rear O2 sensor.

The sensor is located on the rear side of the engine towards the firewall...yes, in that tight space in the back of the engine compartment toward the cabin...lovely. It's really tough to get back there, but making the trip to the auto store to get an O2 sensor removal socket is a BIG help. Do yourself a favor and pick up the socket before you start this job, you'll save yourself a ton of time. I picked up a 7/8" O2 removal socket made by OEM at AutoZone for $16; totally worth it.

All I did was remove the top plastic cover from the engine and literally climbed on top of it in order to get to where the sensor is located in the back. There's really no good way to do it; you'll look pretty goofy, but the job is pretty quick, so you won't have to be there for long. If you bought the replacement O2 sensor, you should know what you're looking for. It's facing up, so at least you've got that going for you. Disconnect the cable first before you stick the socket down there to unscrew it. Use a few extender sockets with a breaker bar to get the old one out; it'll be in there pretty good. Put the new one in, connect it up, and you're done!

There's a lot online about "resetting" the computer so that the check engine light goes out, but I just ran the car for about 4 trips, and the light went out on its own. If the light bugs you, I've heard that disconnecting the battery for a few minutes and then re-connecting it will reset the computer. Your preference.