I have a few questions for you experts. I figure pictures are the most helpful. Following my attached picture:

1. What is this wiring harness? It is a mess of wires and the connections on it are terrible. The white wire is not attached and other ones are just twisted together. I tried looking in the FSM and I could not find out what it was. It is attached to a large black pan directly behind the oil pan on the bottom.

2. Seems to be an unused female plug on the bottom. O2 sensor female end?

3. I am throwing CEL codes which are pointing to both O2 sensors on the driver side. I ordered NGK replacement ones. Then I went under the truck to see if I could spray some PBR on them. I couldn't find them. Have they been cut off? DId someone cut off the cat on that side?

Thanks so much.

Pete

 

Some one gutted the cat on that side. The 4-pin plug that you have labeled #2 in the pic is the connector plug for the upstream O2. It looks like your upstream O2 is missing, and the welds on the exhaust pipe are definitely not factory. The factory cat does not look anything like what you have in that picture. I think it looks like someone removed the cat and O2's on that exhaust bank. No wonder you are throwing codes. I wonder if that 5 pin flat connector goes somewhere on the transmission and that is the cause of the scrolling gear shift indicator in the dash? Looks to me like someone did a number on the exhaust, but I am not sure about the wire or whatever it is in the #3 pic. Maybe a good exhaust/muffler shop could tell you more about all of that but it looks to me like you are missing some important parts here.

Just my 2 cents on it.

Jimmy

 

Yeah it didn't look right to me at all. I have heard of people connecting the downstream o2 sensor to the exhaust and the cel's going away. It's unfortunate but I am not going to drop money on a whole new exhaust. Unfortunately right now I have grinding when I put it in 4x4. I have to investigate that first.

I think for that plug in #3 I will just connect all the wires and see if it fixes anything.

Why would someone cut out the cat?

 

No telling why it was done like that. I have heard/read that you can remove the cat and O2's to get more power out of the truck but I know nothing about that. I believe there are a few guys here that have cut out the cat but I don't know how they did it or bypassed the O2. I think there are high performance cats you can buy too that I guess they flow better so maybe you gain power from it. I have never seen it done but that pic does not look at all like a factory cat. And the O2 sensor and its bung is missing. Maybe the truck is set up so you don't need the O2 that was removed. A performance shop or maybe a muffler shop might be able to look at what you have and tell you more about it. My own opinion on it would be to put it back to factory and see if it runs any better and clears some of the codes.

Maybe some of the 4wd guys here can help with the grinding problem. I don't know much about 4wd myself. It does look like there has been some mods under there, that's for sure.

Jimmy

 

that's not a cat in the pic, that's just a flex coupling... the cat should be (if it's still there ) under the passenger side of the cab... and as far as the wiring goes I'd find a shop you trust and have them take a look at it, just whatever you do don't take it to AAmco, those guys are trained to mess your vehicle up on purpose just so they can charge for more repairs

 

Yeah I don't have a problem doing the wiring myself. Was just curious what it was for and if there is a system in my car that might be having some problems due to it.

As for the exhaust, it looked weird to me. Maybe my car only has one cat and two o2 sensors. I found those easily on the other side. I wonder if that is the case and I bought ones from NGK that were meant for bank 1, would they work over there?

The welds on that left side just look out of place and the fact that there are the female ends of the upstream and downstream for o2's hanging there made me curious.

 

Ok so I did some more research. The california emissions version of this truck have 2 cats and 4 o2 sensors while the federal version has 1 cat and 2 o2 sensors. I might have the federal version right?

If that is the case, why does my truck have the wiring for 4 o2 sensors then? Did all 2002 dodge Dakotas have all the wiring for 4 o2 sensors?

 

As far as I know, all 2001 thru 2004 Dakota's have 2 cats and 4 O2's. I can't remember anyone on here with a 3.9 saying they had only one cat and 2 O2's before but I guess it's possible. I know my own truck has 2 cats. I would think that maybe Dodge did wire the truck for 2 cats and 4 O2's regardless of the emissions system because the different wire harnesses would probably cost more money than just using one harness for both exhaust types.

I think that just from the fact that your truck has the aftermarket welds and whatever that sleeve looking part is, the truck had to have had a cat in that exhaust pipe at some point. You could call up the Parts guys at the Dodge dealer, give them your VIN and they can tell you for sure what exhaust system your truck had when it was built. That is about the only way to know for sure. You may still need an exhaust shop to look under the truck and tell you what that part in the exhaust pipe really is. Maybe they could do that and tell you what the previous owner did to the exhaust and why. Maybe a good shop would at least tell you that much for just a small diagnostic fee.

Jimmy