I've heard the oxygen sensor before the coverter is most important to change out. I'm at 100k in my 2002 325i (E46) and the book says to change them all. My funds are limited. Do you advise that I change out all three, just the pre-converter, or wait till the light comes on? Your advice is most appreciated!
I believe there are actually four oxygen sensors, tow pre-cat and two post-cat. I would only replace the two pre-cat sensors and wait on the other two until they set a check engine light. The pre-cat sensors are actually providing feedback to the DME and will affect performance and mileage while the two post-cat sensors are monitoring the performance of the converters and do not directly affect driveability. Matt
Erich, You can find two pre-cat oxygen sensors pretty cheap on koperformance.com. It looks to be an easy fix too. Good luck.
+1 on the 2 precat sensors. Ill probably do these after I do regulators and vanos. For now my mileage is good I think, especially for my heavy foot. I usually get the needle at 30-25is on the hwy, and the OBC averages around 22mpg depending on how much I'm stomping on it vs. Actually cruising. This is on a 5sp 328 with shark inj, pulleys, and intake with LOTS in my trunk. So I'm not sweating them yet, I suspect the po changed them somewhere between 50k-100k.
O2 Sensors Sannyb - thanks for the link! Great price @ koperformance.com on O2 sensors - about 1/2 price. Is the quality equivalent to that from the BMW dealer?
I think so. I just purchased two the other day and am waiting to get them. The description says that they are BOSCH. Autohausaz.com says that they are BOSCH too so, I assume they'll be the same.
Lots... but mostly trace elements poisening the surface. This is a slow and steady process, and is pretty much unavoidable. Matt
Nope... Oxygen sensors are pretty specialized. To get very simple, they are little batteries where oxygen ions diffuse through a quasi porus ceramic. The current flow is related to the oxygen content. They work over a specific temp range, hence the need for heaters. Pressure sensors tend to be diaphrams that couple to either a capacitive or resistive circuit, ie they are mechanical. Newer ones are based on MEMS fabrication techniques (like for a MAP sensor) but it's just a smaller version of the same thing. Fluid level sensors can be lots of types. Matt
Hey Erich, I just got my O2 sensors in today and replaced the old ones. They are the same (Bosch). Same numbers on the sensor bodies. Took me under an hour. Be careful pulling the cover off of the sensor tip. They already have anti-seize on them. Good luck. -Sannyb
