Oxygen Sensor Question

[MyTaurus8AChevy]

2004 Taurus. I have an important question about the oxygen sensors.

Do they get their ground signal by being mounted to the exhaust, or do they get their ground signal via the wiring harness?

In other words, if the oxygen sensor was plugged in but NOT mounted, would it still work correctly?

[65comet]

Are you trying to have the oxygen sensor outside the exhaust pipe in hopes that it will read good outside air and pass an emissions test? I'm pretty sure that won't work. There is a thread here somewhere that explains how the sensors work. The exhaust has various flanges and rubber isolated mounts, not good conductors for a ground. I'm pretty sure the sensor has two wires, so I'm going to say one is for ground. If I wasn't in the office and have a meeting in a few minutes I'd verify this info and find that thread for you.

[MyTaurus8AChevy]

Originally Posted by 65comet

Are you trying to have the oxygen sensor outside the exhaust pipe in hopes that it will read good outside air and pass an emissions test?

No.

Some background; My car does not get a catalyst test reading when I take it for the emissions test. They keep saying that their computer 'can't access' that part of my computer, and to keep driving the car so it "resets". Problem is I've been driving the car for almost a year now and it still never resets.

The car was running 100% for as long as I've owned it (around 5 years now). It was the most dependable car I've ever had, bar none. Then I bought a new Milan and didn't trade the car in because they wouldn't give me a fair price for it. I was planning on selling it myself but then my father died and so I parked my car and decided to sell it after matters settled down. Problem was my mother was also dying of Alzheimer's and I was her only caretaker. She passed away around 6 months ago. Long story short the car sat for around two years and then it wouldn't start, and even the few times it would start it ran terribly bad. After looking into it I decided that the only thing that made sense was that it had to do with bad gas gumming everything up. So I flushed the gas tank, installed a new fuel filter, plugs and oxygen sensors. It now runs great again BUT I cannot get it reset the catalyst test.

I can no longer drive it on the street because they only allow two 30 day tags before I can get plates BUT without it passing the emissions test they wouldn't allow me to buy plates. That's become a whole other ball of wax. Right now I just need to figure out how to get the car to pass the test so I can proceed onto the next phase (getting plates).

I've been doing everything that I can imagine to try to figure out what the problem is with the car not being able to pass that catalyst test. Then I remembered last week that when I installed the bottom oxygen sensor that it might not be properly grounded, and if that's the case then "maybe" that's why the cars computer won't reset the catalyst part of the test.

You see the old bottom oxygen sensor was fused solid to the exhaust pipe. I had many people look at it but no one could get it to budge. Then one mechanic told me that I could buy a new threaded fitting and simply drill a new hole in my exhaust and install the new oxygen sensor there, which made sense. So I ordered the fitting and mounted the new oxygen sensor around an inch from the one that was stuck. I was told that I would need to weld the fitting on the exhaust pipe, but because of dealing with paying for both funerals I am in deep debt and have no money for welding, so I drilled the hole slightly larger than the new fitting and hammered it into place. It was a tight fit, but I knew that when the exhaust heated up that it would expand so I also put high temp adhesive all around the fitting to keep it in place.

Here's the reason for the question; if the new fitting was welded into place then I know it would be grounded through the fitting and oxygen sensor threads, but the way it's mounted now my theory is that maybe it's not being properly grounded, and that's why the cars computer doesn't see it. If the oxygen sensor gets its ground through the wire(s) then I am once again stumped as to why the car can't see it, but the "ground through the exhaust" issue sounded logical, so I was looking into if it was a possible solution. Hope that all makes sense.

Originally Posted by 65comet

If I wasn't in the office and have a meeting in a few minutes I'd verify this info and find that thread for you.

If you get a chance then that would be great. I'm grasping at straws trying to figure this out.

[shorod]

Years ago there were single wire O2 sensors that relied on the exhaust system as the ground reference, but with OBD-2 the heated oxygen sensor became common and has a dedicated return path for the sensor element as well as the heating element. On your car the sensor return path will be the Gray/Red wire for each of the 4 sensors.

-Rod

[shorod]

Do you happen to have a scan tool that will allow you to monitor the 4 O2 sensor readings in real time with the engine running ("Datastream" or "Live Data" modes)? If not, you should be able to pick one up for less than $200 (much less if you have an Android phone with the free Torque app and OBD-2 dongle. You can get Bluetooth dongles for around $20 that will in all likelihood work just fine for what you're trying to do.

-Rod

[MyTaurus8AChevy]

Originally Posted by shorod

On your car the sensor return path will be the Gray/Red wire for each of the 4 sensors.

I only saw (and replaced) two sensors. Might this be why the cars computer can't reset?

[shorod]

Originally Posted by MyTaurus8AChevy

I only saw (and replaced) two sensors. Might this be why the cars computer can't reset?

Possibly. There should be one sensor in front of each catalytic converter and one sensor after each converter for a total of 4. It's also possible that you will have 3 sensors if your car only has one converter after the two downpipes are y-ed together. I pulled up the diagrams for a 2004 Taurus with the FFV engine since I didn't see any detail on which engine your car has. Maybe the non FFV vehicle only has a single converter? But at a minimum you're missing one of the O2 sensors.

Edit: I just checked the diagram for the gasoline engine, non-FFV 2004 Taurus and it also lists 4 O2 sensors.

-Rod

[MyTaurus8AChevy]

Originally Posted by shorod

you should be able to pick one up for less than $200 (much less if you have an Android phone with the free Torque app and OBD-2 dongle.

Thanks Rod! Is this the correct Torque app that you were talking about?

https://play.google.com/store/apps/d...dsLnRvcnF1ZSJd

[shorod]

Yeah, looks like it. Since I have the Torque Pro app that link automatically takes me to Torque Pro (which runs around $5). Torque Lite is free. I have a couple of different bluetooth dongles, both were around $20, and one works with almost no errors, but even the one that has errors still should work fine for your purposes. The one that works less well I picked up off of eBay, the "better" one I picked up from an online store, but I don't recall which. This evening I could dig through my receipts and probably find out where I got it if you're interested.

-Rod

[MyTaurus8AChevy]

Originally Posted by shorod

This evening I could dig through my receipts and probably find out where I got it if you're interested.

That would be GREAT! I do have a bluetooth dongle but I don't know if it will work with this app. I will also try to contact the app developer and see what they recommend. Any help trying to figure this car out is greatly appreciated!

[MyTaurus8AChevy]

Here is a list of dongles recommended by the developer. Could you look and see if the one you're using is listed? Since funds are so limited I'll only be able to try one.

http://torque-bhp.com/wiki/Bluetooth_Adapters

[shorod]

The Vgate Scan Bluetooth adapter in the middle of the "China/via eBay/Amazon" list is the same case as the one I have that suffers from errors. The one below it is similar to the one I have that works quite reliably, but mine has a black housing.

-Rod

[MyTaurus8AChevy]

To clarify, this is the one that works OK?

http://www.amazon.com/ELM327-MINI-Bl.../dp/B0079G1JU8

[shorod]

Correct, assuming there are not a bunch of different guts in the same housing. That unit looks identical to the one I have that suffers from errors, but is still quite useable.

-Rod

[MyTaurus8AChevy]

I was looking at the Torque app and was wondering what display setting(s) I need to look at my car, O2 volts?