what is the problem with my 99 civic with the code p0135

Question

I have a check engine light on in my 99 civic hatchback.
Code P0135.

Where is this sensor located? I believe it is an 02 sensor.

Answer 1

P0135 is for air to fuel ratio sensor (oxygen sensor) bank 1 sensor 1.

if it behind the radiator on the exhaust manifold. see picture below