church

My engine light is on due to a bad oxygen sensor, the code is P0135. I have never worked on a Civic before; and I am having trouble figuring out which O2 sensor actually needs to be replaced...


Is it this one? - A



Or this one? - B



My next question, and this is the reason I am confused; the reason I ask is because what is titled as the "lower" is the one that appears to be on the upstream part of the engine, and the "upper" is completely under the car it appears...

I could use a little help, I am kind of confused on this one. Thanks!

church

Also, please understand that I am new to the civic world. I switched from a Mazda RX8; so rotary is really all I know right now...

ezone

Have you been under the car to look at each one? They are obviously different (wiring length and covers, and connectors).

An EX has the cat under the car. Others can have the cat attached to the manifold.



On ANY vehicle
Upstream (primary) and downstream (secondary) refer to exhaust FLOW, not necessarily their placement on the vehicle. FLOW begins at the engine, ends (exits) at the tailpipe.



The primary is closest to the engine -- relative to the exhaust flow. Could be right on top, could be underneath. All depends on how it is plumbed...I could run the pipes up over the roof and upstream/downstream do not change places in the flow.

Primary is always the first in the exhaust flow though.

The secondary is located after the primary. In many cases it is screwed into the middle of the CAT, or just after the cat.


I bet you can't explain how they got a triangle shaped piston to walk around an oblong circle.

church

Thanks for the reply. What I really need to know is if the code P0135 is the primary or the secondary O2 sensor...

ezone

Google the code number "P0135"
http://www.obd-codes.com/p0135

O2 heater circuit failure.
Bank 1, sensor 1.

Sensor 1 is first, or primary.

Bank 1 --- your 4 cylinder engine has only one bank.
A "V" engine would have 2 banks, for example.


HTH

church

Awesome. Thanks so much for the help!

lowlife9

you can also use DENSO brand oxygen sensors NTK are more expensive.