Oxygen sensor

[mech9T8]

So my check engine light goes off and the dealer says I need to replace the O2 sensor. They wanted about $350 CAD.
So I thought I would do it myself and while I was at it I would replace all 4. But after seeing what one of them costs I decided not to.
What I need to find out is which one is faulty. The dealer told me that it is the sensor from bank #2. So are these the ones before or after the cat? Anyone know? Is there a way to test them? I found out that all 4 sensors are identical but then I also found that there are some with short wires and some with longer wires. So which one do I get?
I thought that if I get the one with the longer wire I would be safe because it would reach to the connector regardless.
Any help would be much appreciated.

[Sk1d]

I'm assumin u've either got a straight six or a v8 in ur Beemer. Bank 2 meaning one side of the exhaust system or the other. If u can speak 2 ur mechanic again n ask him if its the upstream or downstream sensor ur sorted. After that its a DIY job...

[mech9T8]

I have a 96 328.
I don't think the dealer will be that willing to give up the info.
But I can always try.

[okczy21]

if you get an aftermarket exhaust system doesnt it just do away the oxygen sensors anyways, why are they there?

[Sk1d]

See wat u can do bout gettin sum more info off em... might get lucky...

Good luck...

[///M Power]

4444444444 O2 sensors? hat's a new one to me. If u got an i6 i didnt think there wud ever be more than 2. hmmmmmm

They are easy to change if u got a u wrench of some sort. You need to give us a year adn a model. And $350 is wayyyyy too $$$$$$$$$ even for canadia

O2 sensors sense the amount of chemicals in ur exhaust waste and thus use a computer to adjust the fuel injection system to provide better gas mileage. YOU NEED IT.

[mech9T8]

OK the dealer told me that bank #2 is the right side of the car but I still don't know if it's the one in front or behind the cat.
I still need to figure out how to tell if the sensor is bad.

[okczy21]

so do aftermarket exhausts not use the o2 sensors? or do they?

[Sk1d]

Okay, this is where it gets a bit more tricky... If u can get ur hands on a multi-meter u need to check the voltage across 2 of the sensor wires with the sensor still plugged in and the engine warm and running. Not sure wat color the wires will be but u can easily check em all til u get the right 1's. When u probe the 2 correct wires ur meter should show the sensor's voltage switching between about 100 and 700 mV, if the sensor's working correctly...

Hope sum of this helps out...

okczy21, if u bought a cat back system the oxy sensors stay in the system in the original cat' pipe. Dunno wat happens to em if u bought a de-cat pipe tho, sorry...

Sorry guys, tha shoulda been voltage not resistance...

[BeachBunny]

He's asking $350?! This is just something I remember hearing... but can't you replace your oxy sensors for like 85 bucks?

[Henri]

Ok my dealer told me the same thing on my 318i... I refuse to let them change it since I got no Check Engine light lighted??!!!

I'm from Canada too... the 2 sensors cost 178$ and 75$. The cable is longer, yeah, but the connector is different also... you can't take 2 times the 75$ sensor.

If you can do an oil change all by yourself, you should be able to change those.
http://www.geocities.com/e36rulz/DIY.html

I got a question for you... If I ever realize they were right (assuming I should change these parts), are BMW original oxygen sensor better than Bosch oxygen sensor??

Thanks a lot!
Henri

[mech9T8]

So I crawled under my car this weekend and found all the sensors.
I was able to access the 2 at the rear and I tried to check them for voltage output with a digital multimeter but I didn't get anything conclusive. I have to try the ones at the front now. And this time I'll try to check the resistance too (thanks for the input SK1D). But one thing I noticed is that they are not going to be easy to remove. Wish me luck.

Henri, from my research I believe that the sensors from BMW are Bosch sensors. I've looked around and believe it or not the dealer has the best prices on a new sensor...$178 CAD. You can try to get a used one to if you want. They are cheaper but won't last as long.

[Sk1d]

Okay, this is where it gets a bit more tricky...

Sorry guys, tha shoulda been voltage not resistance...

[Henri]

Yeah... that's the 1st time I see cheaper parts at a dealership lol

Anyway, I presume I don't have to change them 'till the Check Engine light is on... right ?

Thanks
Henri

[mech9T8]

Yep.
I read that you should change them after 60,000 miles to ensure good engine performance but I'd wait till you see that check engine light.
Ultimately the choice is yours.