I have a 1999 Honda Civic EX EJ8 D16Y8

In the service manual, the instructions on changing the O2 sensors on the D16Y8 motor show 1 O2 sensor in the Exhaust Manifold and 1 after the Cat. On my exhaust manifold, however, there is no O2 sensor nor a hole for the O2 sensor to bolt into. After a bit of investigating I find that my exhaust manifold is exactly the same as this one found at this ebay link

I have 2 CEL codes, P0136 (o2 Bank1 Sensor 2) and P0158 (o2 Bank 2 Sensor 2)

I understand that Sensor 2 means after the cat, so since the codes aren't screaming about Sensor 1 (pre cat) should I not worry about my exhaust manifold not having an o2 sensor? OR does it not having an o2 sensor cause more problems for me.

 

If its exactly like the eBay one you linked, then u are missing the B pipe which hold the 1st O2 sensor. Then your cat converter bolt onto that b pipe, then the 2nd O2 sensor is behind the cat converter. Followed by the rest of your exhaust system.

Get it?
Header, b pipe with O2 sensor, cat converter with 2nd O2 sensor, mid pipe and resonator, then muffler.

​​​​​​Look at this. @ EX/Si photo.. Not DX/CX..
http://www.hondacivicforum.com/forum/mechanical-problems-technical-chat-8/96-00-civic-exhaust-help-74841/

See which part you are missing. Replace it..

 

Wow damn, thank you so much for your help, I was thinking that someone did a shady job on the exhaust.

 

Honda calls the pipe that goes from the manifold, under the oil pan, to the inlet of the converter "pipe A" -- the long pipe under the center of the car starting at the converter and going back to near the right rear wheel is "pipe B". Pipe A also commonly called the "front pipe".

 

I stand corrected.
thank you for the correct info..