I'm popping a code 17 which indicates a faulty signal from the O2 sensor. They default on failure is shutdown of the feedback system. What have I lost until I get a new O2 sensor? Could this cuase a code 12 and a hunting idle when the engine is cold? I have that issue as well. I've already put three different TPS and adjusted them IAW the manual using the light.

 

the feedback system makes small changes to engine fueling in order to make the exhaust AFR fluctuate around 14.7:1 for best overall emissions during cruising.

you may have somewhat worse gas mileage, but this isn't going to affect idle.

 

The feedback system is the continual readjustment the ECU does to the mixture to keep the car running at or near the stoichiometric mixture (14.7:1). It does this by watching the voltage from the O2 sensor, and then lengthening or shortening the pulse width to the injectors to richen or lean the mixture. Feedback operation happens only under non-idle, steady rpm operation (cruising).

If the ECU does not see the O2 sensor signal, it will go into a limp mode, where it runs very rich and does not adjust the mixture. This will allow the car to run, but over time it will cause some problems. The rich mixture will tend to foul the plugs, and that can show up as other problems. Also, the rich mixture causes the cat to run very hot, which can be a fire hazard, and if it goes on for a while, it will 'cook' (ruin) the cat.

I found that sometimes, when the O2 was not present, the ECU would incorrectly judge that the O2 was present and then try to adjust mixture using the non-existent signal. When it did that, the car ran *terribly*.

Don't leave the feedback system out of operation for long. A new cat costs a lot more than a new O2 sensor. Check the wiring from the O2 sensor to the ECU first; no sense buying a new sensor if the wire is not connected.

You don't have to get the 'OEM replacement' sensor ($60). The only difference between that and the generic one is the connector. Just cut the connector off your old sensor and solder the wire onto the new sensor lead and you can save $40.

If you change the O2 sensor yourself (not a really difficult job), you will need a special socket. Harbor Freight has two types; a deep socket with a slot down the side for the lead, and a 'crows foot' style. I recommend the crows foot, as the deep socket isn't quite deep enough.

 

I got the new O2 sensor installed this weekend. They special socket works wonders. I had to use an impact wrench to get the thing out. That was the hardest part of the job, getting the impact wrench in there. Good thing it wasn't my t2 which has ABS, I would have had to remove all that stuff or jack the car. I don't mind jacking the car, but I have a 2 and 3 year old boys that want to be under there with me.
I do have two questions. Why is there such a price difference between OEM 89.00 and the Bosch one 20.00? I expected a little price difference, but not that much.
Okay, here's the puzzler. I cleared the fault codes by disconnecting the battery and confirming the 12 and 17 code came back. They did. I changed the O2 sensor cleared the codes and started the car. The idle was smooth at 850 (I like it a little high) and BOTH codes were cleared. I did notice that there was a lot of sulpher smell from the exhaust that I didn't notice before.
Any thoughts?

 

Just wondering if code 17 or any other codes came back or changing the o2 sensor actually fixed the problem? any updates?