Rep Power: 0

Trying to help my son with a 2001 civic he just bought. Check engine light was on when he bought it. Previous owner said it was the downstream o2 sensor and he wasn't worried about it. That is why the light is on. I scanned it and that is the only code. So we got a new o2 sensor, to get the light off, so we will know if something else throws a code in the future. The problem is that the previous owner had the sensor unplugged and wire tied up on the front of the engine. We can't find the corresponding plug to plug the new sensor into. I don't know if he tied that somewhere else or what. Where does the harness for the downstream o2 sensor go? If I know where it's supposed to b, maybe I can find it. Thanks.

 
Rep Power: 518

What car do you have? Coupe? Sedan? EX? LX? DX?

What engine does it have? D17A1? D17A2? Something else?

Where is the cat located in the exhaust system?


Stock DX or LX with D17A1 engine should have both sensor connectors within a couple inches of each other. If one is in the right spot, the other should be right next to it.

 
Rep Power: 0

The car is a sedan. Not sure on the dx,lx,ex thing. It doesn't have any emblems on it. Also not sure what engine, I do know it says vtec on it, if that helps. Also not sure exactly where the cat is in exhaust. When I was looking for the connector I didn't really notice where the cat was. The downstream o2 sensor is in a vertical section of the exhaust before it turns toward the back of the car. Sorry for the lack of info, but the car is not here right now for me to go out and look at. Thanks for your response and I will try to get a better description when he is home with the car.
Oh and the pigtail that comes off the downstream o2 sensor isn't long enough to get near the plug location for the upstream sensor(which is right in front of the radiator support).

 
Rep Power: 518

Are you in Canada or US?
PM the VIN to me, I'll see if I check it further




The engine type is stamped into a square-ish pad on the engine here:




2 choices if it is using stock components:

One version has the cat built in to the exhaust manifold, the other version locates the cat underneath and behind the engine.

First version:



^^That pic shows both sensor connectors within inches of each other for this version.

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Second version would have tubular header pipes up close to the engine hidden by the heat shields, and the cat would be 2 or 3 feet further downstream of this.





If it has this version, the rear sensor is screwed into the side of the cat (or just past the cat) under the car,

the sensor connector should be below the steering rack, near the bottom of the firewall and just to the passengers side of the "hump", looks like maybe a 6 inch length of wire where it comes out of a main harness.


HTH

 
Rep Power: 0

Wow, what great information! It looks like its the first version you listed. But that connector isn't there. It doesn't look like the pigtail for the existing secondary sensor that is installed will reach that high, but he may have it looped and its longer than I thought. As I was looking for the connector under the car, I noticed several places where hoses and wiring harnesses were not in there "keepers", which makes me think that the motor may have been out of the car at some point and not put back in very neatly. If that's the case then it could be that the connector that I'm looking for may not even be where it is supposed to be exactly (pushed back behind something). I'm gonna take a closer look in that spot and any nearby spots where it might be hiding. Thanks so much for all the great info.

 
Rep Power: 518

Swapping a non-original engine is awful popular (VTEC engine into a non-VTEC car) as is swapping exhaust systems (especially after a cat goes bad or a manifold cracks), and it leads to situations like missing wiring and sensors that cannot be connected due to differences in harnesses and wiring between different versions of the cars.