ka11v

Hi, kinda new to this so take it easy on me...lol anyways, I have a 97 A4 and need some advice/help with a few things. I went into a ditch in a snowstorm and lost my driver side catalytic converter, and now I believe there is a whats left of a O2 sensor hanging down where my cat was. I ordered a new cat and it just came in from eastern catalytic, my question is where does the O2 sensor go into it? Also, where can I get cheap O2 sensors, preferably not online cause I'd like to get this done today. Thanks.

AudiMick

There are two O2 sensors per bank on an A4. So (4) on a V6. Pre and post cat. Pre-cat controls mixture, the post just checks efficiency.

The original OEM has the ports in the assembly, if you bought an aftermarket cat maybe not.

ka11v

yeah, it is aftermarket and I don't see any ports for any sensors so is that still okay to use? I assume it must be if they didn't include the O2 ports? I was just curious because there are the wires hanging down where the old sensor was before it got ripped out. Is it okay to just replace the cat and exclude the post sensor or will it make my car run badly? Thank you.

Bobby Kinstle

Most auto parts stores carry the O2 sensors for our cars. Just be sure to tell them it's the rear sensor and on which side it's on. It may be extremely tight and you must not use any oils to break it free or the left over oil will destroy the new sensor in short order. It comes with anti seize for the threads and that you do want to use.

Excluding the post cat sensors will not hurt the engine but it will make the CEL come on and you will fail smog check if your state requires them.

ka11v

okay, so technically I don't need the secondary O2 sensor? I'm only replacing the cat on the driver side, and the pre cat sensor is still there, so not having it won't hurt me any? This is what the cat I ordered looks like just so you have an idea.

Bobby Kinstle

Correct as long as you don't mind having the Check Engine Light on 100% of the time and you don't need to pass a smog check.