Hi,

This is my first post to the forum so a Hi to all the members. I am looking for some information. I have a 2002 330i with around 22,000 miles on it so it is really low mileage. It just came off warranty and the "Service Engine Soon" light came on. Just my luck! I am not at all happy about it and it seems really convenient that it happened after the warranty ends.

Anyways, I took it to the shop and they told me that it was a bad oxygen sensor. They also told me that the car had 4 oxygen sensors 2 before the cat and 2 after. I was also advised to have 2 of them replaced at the same time as I was told that sometimes after replacing one of them, the other one goes bad soon and to save on labor they were recommending that I replace 2 of them together. They also told me that it is difficult to distinguish which one of them is bad. I thought that sounded strange. Anyways they quoted almost $600 for it. Is that a good price? I thought it sounded really steep. What do you guys think about it?
I also think it is really soon for an oxygen sensor to go bad and I wonder if it a statement on the quality of BMWs. My car is impeccable maintained and I actually perform oil changes every 7500 miles. How could the oxygen sensor have gone bad so soon? What causes an Oxygen sensor to go bad?

I would appreciate any advice. Thanks a lot.

D

22k is way too early to be having O2 sensor failures. There can be other faults that will masquerade as O2 sensor faults. In particular improper mixture (intake leak, misfires, contaminated MAF, bad CCV, bad CPS) can cause conditions that cause an apparent O2 sensor fault.

At that mileage, I'd swap the bank 1 & 2 sensor (pre-cat or post-cat, which ever is throwing a fault), clear the stored DTC's, and see if the fault follows the sensor. If it does it's a bad sensor. If not you need to start looking for other problems.

22k is way too early to be having O2 sensor failures. There can be other faults that will masquerade as O2 sensor faults. In particular improper mixture (intake leak, misfires, contaminated MAF, bad CCV, bad CPS) can cause conditions that cause an apparent O2 sensor fault.

At that mileage, I'd swap the bank 1 & 2 sensor (pre-cat or post-cat, which ever is throwing a fault), clear the stored DTC's, and see if the fault follows the sensor. If it does it's a bad sensor. If not you need to start looking for other problems.

I agree

Can we mabye get a sticky on check engine lights and mabye some OBDII codes?

Something that says "Take it to autozone, get your codes read for free, look them up on google, get some information, then post for help" ? Not jumping on the OP here, he didn't do anything wrong, although having the code handy might help us more.

As for them not being able to tell which one it is, I THINK I know what they're saying, but without the code, I really have no idea.

If they get a code that translates to "catalyst efficiency below threshold", and assuming its the oxygen sensor giving a bad reading (could very well be the CAT), you don't really know if the pre-cat is reading too high or the post cat is reading too low, see what I mean?

Typically, if I get a code like that, I reset it twice before I take it seriously. Even though autozone reads OBDII codes for free, I recommend getting a code scanner anyway. You can read and reset your own codes and won't have to pay the dealer $150/pop to reset them each time.

My recommendation -- try replacing the two pre-cat sensors first. It's a much easier job than replacing the post-cat. I recently did all four and probably can talk you through doing the precat if you want to do it yourself. The sensors alone are very expensive so why not save the cost of labor. I have a 2001 325ci but I imagine the steps will not be different. There are also some very good posts on the net on this that I can refer you to; same ones I used in conjunction with the repair manual in doing the work. If you get the same error, you can then try to do the post-cats but that was a frustratingly time-consuming task, not because of difficulty but because of the tight space you need to get to in order to get it done.

Hi,

Thanks a lot for all the helpful replies. I think I have finally found a really helpful BMW site. Thanks a lot. Well, since I am pretty naive about cars and too nervous to DIY, I had the shop replace the O2-sensor. They replaced 2 for $540.00. I don't know if it is a ripoff but I am sure it would probably be a lot more at the dealer. The "SERVICE ENGINE SOON" light is no longer on. Thanks.

D

can anyone tell me where the rear o2 sensors are exactly on my 2000 e46 just did the front ones and my light still comes on once in a while.

I thougth the factory warranty lasted for 50,000 miles. And I'd find another shop and get a second opinion as well. My 02 sensors are fine at 108,000 miles.

I thought it was 50000 miles or 4 years whichever was first. Well it is more than 4 years. Isn't that the case or am I misunderstanding the warranty?

The CEL on e46's is called "Service engine soon"?

dang - well if you need to replace them, it's a very easy DIY. Also - you should try autozone for the bosch part number for your O2 sensors. I was able to get pre-O2 sensors for my old 540 for like $60-$70 apiece.

I thought it was 50000 miles or 4 years whichever was first. Well it is more than 4 years. Isn't that the case or am I misunderstanding the warranty?
No, you are right. I'm sorry.

BMW5763, post-cat O2 sensors are just after the cat, under the car. You need to lift the car and get underneath to see them. You may have to remove one of the panels (or both if they are interconnected); I did not have to remove mine in order to see the sensors. On mine (2001 325ci), they were slightly towards the passenger side; on the passenger side of the oil pan and slightly further towards the rear. They should be connected to the exhaust fairly close together so if you find one, you'll find both.