Bad Oxygen Sensor?

So I was on a telephone interview the other day in my car (didnt want the boss to hear) and it was quite warm out 85-90 deg f. I had the AC on and was idling for about 20 minutes or so. When I finished the call I noticed that my check engine light came on?

 

It stayed on for a couple days with no visual or physical problems with the cars performance, then it went away. I played it safe and brought it into the dealership anyways. (43k miles on odometer) and they pulled an Oxygen Sesor code? They said it should be replaced, but at$250, its a little steep.

 

The car seems to be running normal but I am unsure if I should replace it, since the check engine light is now off?? My plan was to wait and see if the check engine light comes on again, if ever.

 

Thoughts would be much appreciated!!

 

Thanks

Joe

The O2 sensor is easy to replace. Takes all of 5 minutes. I got mine from THEKINGOFPARTS at a much much much better price than the $250 they asking.

My O2 sensor went bad because of the Perrin Headers and Rallitek skidplate combo. I didnt pay attention to clearance when I put them on.

Yeah, I replaced mine a while back, and it was pretty painless. Also ordered online, so the part was less than half of your quote. All you really need is an offset O2 sensor socket, maybe $10. In a pinch I think a 7/8" wrench can work too.

O2 sensor socket is $5 if you have a Harbor Freight nearby. Autozone and such will normally lend the tool for free. Or, like the previous post, an adjustable wrench.

Yeah, replace it a faulty O2 will cause your car to run slightly rich and worsen your gas mileage. All which sensor did they say was faulty, the front or rear? This to would factor into my decision as the rear O2 is not important.

Which O2 sensor is it? Everyone is assuming it's your front since that's the one that's most sensitive, but double check your codes.

Just reinstalled one in the wife's A4, a 7/8" wrench does work fine. But like others have said confirm which one is bad. The first one is used for fuel/air corrections and the second is used to confirm if the cat is operating efficiently. In the wifes car I had to use spark plug defoulers to move teh second sensor out of the air stream due to a HFC throwing CEL. But I only did this because I checked the resistance across the heater and confirmed the sensor was still good. Otherwise I would have repalced it.

Thanks for all of your great responses. Does anyone have a photo or tutorial on this. To be brutally honest, im not quite sure where to even look? Can you access it just under the hood, or do you need to get underneath.

 

Also - i have a Perrin drop-in filter, do you think that could be screwing things up? FYI, i recentlly (2 months ago) cleaned it and used my K&N recharge kit to re-oil it......

 

It is my FRONT 02.

 

Thanks

The drop in would not be the cause. The front O2 is located behind the passenger side fender well on the exhaust manifold that attaches to the uppipe. Basically remove the passenger side wheel and pop off two popets to the fender cover and it is right there.

Doesn't seem too bad... If yaw'll think it is worth replacing, I will start looking into ordering the part and borrowing the tool from autozone and get er done.

 

thanks again

i would first check the resistance of the sensor. see if the resistance across the top two pins is around 2.4Kohm....if it is much higher or lower, then it is the O2 sensor.

Amazing the O2 sensor in my '05 Legacy GT went bad at around 43K also. I had been driving it for about 3 weeks when the cruise control quit operating & the check engine light came on. Since nothing was open on Sat I returned home, then the next time I drove the car it started to sound like a muffler had a hole in it. When I put it up on some ramps I found the O2 sensor blew out of the exhaust. The sensor was hanging by the wires, & the threads of the sensor were still in the exhaust.

 

After a few days of talking with the dealer, & the person who was in charge of the drawing for the company vehicles at SIA I'm finally getting this problem fixed. Right now I'm driving a loaner Outback wagon until the repairs are complete.

i would first check the resistance of the sensor. see if the resistance across the top two pins is around 2.4Kohm....if it is much higher or lower, then it is the O2 sensor.

 

Now, wouldnt the shop have to do all that, not sure i have the equipment to check the resistance. I already paid $35 for the diagnostic FEE so doubt im going to bring it back just to burn a few more dollars.

 

Can autozone check that for me???

Amazing the O2 sensor in my '05 Legacy GT went bad at around 43K also. I had been driving it for about 3 weeks when the cruise control quit operating & the check engine light came on. Since nothing was open on Sat I returned home, then the next time I drove the car it started to sound like a muffler had a hole in it. When I put it up on some ramps I found the O2 sensor blew out of the exhaust. The sensor was hanging by the wires, & the threads of the sensor were still in the exhaust.

 

After a few days of talking with the dealer, & the person who was in charge of the drawing for the company vehicles at SIA I'm finally getting this problem fixed. Right now I'm driving a loaner Outback wagon until the repairs are complete.

 

Had the same thing happen to the second O2 sensor when my car was a few months old. The bung welds were missing. The bung was tacked but the bead was absent.

I doubt Autozone will check the resistance, typically they'll just read codes and won't interpret them either. Just give you a print out of the DTC's. all you need is a multimeter and to be honest they are a good thing to have and you can get one for like 20 bucks at Sears. As for whether or not they actually checked it...depends on the dealer. Most of the time it is not worth it for them to spend the time since they can just sell you a new one with mark up and then charge you for the labor too.

So, all in all, even though the check engine light hasn't come back on, Im getting the feeling from yawll that I should just replace it - head to autozone for the wrench and order the part myself.....

 

And, when you pull the passenger fender molding off, the O2 sensor is literally right there? Is there anything particular I should know when uninstalling and re-installing them?

I don't know for sure with the suby but I know on the wifes A4 the first one is the important one, it adjsuts your air/fuel mix....so if this one is questionable I would defiantely recomend replacing. The second one is used to confirm that the cat is operating correctly. This is the one I recently spaced out in the wifes car since it was seeing too much airflow due to the HFC.

And, when you pull the passenger fender molding off, the O2 sensor is literally right there? Is there anything particular I should know when uninstalling and re-installing them?

Yes, right behind the panel. Installation is pretty straight foward, unscrew then screw back in. Use a regular 1/2in wrench for the O2 socket.

So, all in all, even though the check engine light hasn't come back on, Im getting the feeling from yawll that I should just replace it - head to autozone for the wrench and order the part myself.....

 

And, when you pull the passenger fender molding off, the O2 sensor is literally right there? Is there anything particular I should know when uninstalling and re-installing them?

 

If CEL did not come back on, I would not worry about replacing it. Jus ttake the time to check resistance and get the wheel of to learn more about the car.

A datalog under cruise conditions will quickly tell you whether or not your front O2 sensor is bad. All you need is a laptop and a cable (tactrix cable = $80, VAGCOM cable = $20).

For $100 bucks in cables and computer equipment, I can probably just replace it and forget about it.... appreciate the intelligent idea though.

If you have a laptop all you need is the VAGCOM cable which is $20.

A datalog under cruise conditions will quickly tell you whether or not your front O2 sensor is bad. All you need is a laptop and a cable (tactrix cable = $80, VAGCOM cable = $20).

 

Assuming no CEL, what exactly in the log would indicate that the front O2 sensor is bad/lazy ?

Front or rear sensor? Are you running a catless downpipe?

unclemat, datalog OL/CL status, throttle position, MAF and AFR. When the OL/CL status is 8 and the throttle position is constant and MAF is constant then the AFR should read 14.5+-0.5. If it oscillates wildly then it is bad.

 

The front O2 sensor doesn't respond immediately so there will be some variations.

 

BTW, Subaru calibrated their O2 sensor to 14.5 as stoichiometric. However, when it reads 14.5, the true reading is actually 14.7.

 

You can experiment with my CL fueling spreadsheet here:

 

http://www.enginuity.org/viewtopic.php?t=1871

 

I used it to calibrate my MAF for low MAF load.