Pre-cat Oxygen Sensor DIY (lots o pix)

Great write up

I replaced both pre-cat oxygen sensor yesterday, and the engine light on immediately and have the following codes

CA- oxygen sensor control limit, cyl 1-3
Cb- oxygen sensor " ", cyl 4-6
e4- oxygen sensor adaptation limit #4-6
e3- oxygen sensor " ", 1-3

Any one has similar experience? Should I replace the post cat oxygen sensor as well?

Codes have gone after replace the after cat o2 sensors.

Very good write-up, but FWIW, for M3s (and I think this is worth adding to the DIY), one must remove the heat shield(s) to gain access to the sensors. I wasn't aware of this, so in the middle of the job, I was wondering where the heck the sensors were. I did figure out that the heat shield should be removed, but I still think it's worth mentioning.

All in all, good write-up and thanks!

Anyone know what happened to the pics? For some reason they are not displaying.

Can the OP re-host the pics? I need to change my 02s

Bah. I burned my website to the ground, laughing the whole time. I'll re-host them eventually but I'm unmotivated. :/

I own a 2003 325i and I have not been able to drive it for a couple weeks - it is stored in my garage. I have described the entire problem here: http://www.e46toronto.ca/forums/show...8&page=1&pp=10

But pretty much, the engine turns over, idles extremely rough, and then stalls after a couple seconds. I bought a Peake tool and the code was E10 pointing towards pre-cat o2 sensors and/or camshaft position sensors. I was told only the INTAKE CPS should cause the engine not to start so I replaced it today but did NOT fix the problem. I don't want to replace the exhaust CPS if it doesn't even affect this problem.

I am stuck for ideas. From reading this thread, seems like my problem could be pre-cat o2 sensors as the fault code reads (although I didn't think this would cause the engine to not start) or oil separator, etc (as one person in this thread has noted - he mentioned his code pointed toward the o2 sensors but the actual problem was different).

Any ideas? Should I go ahead and change the pre-cat o2 sensors or is there any way to tell the exact problem before going ahead and purchasing parts?

Originally Posted by charles_316

I own a 2003 325i and I have not been able to drive it for a couple weeks - it is stored in my garage. I have described the entire problem here: http://www.e46toronto.ca/forums/show...8&page=1&pp=10

But pretty much, the engine turns over, idles extremely rough, and then stalls after a couple seconds. I bought a Peake tool and the code was E10 pointing towards pre-cat o2 sensors and/or camshaft position sensors. I was told only the INTAKE CPS should cause the engine not to start so I replaced it today but did NOT fix the problem. I don't want to replace the exhaust CPS if it doesn't even affect this problem.

I am stuck for ideas. From reading this thread, seems like my problem could be pre-cat o2 sensors as the fault code reads (although I didn't think this would cause the engine to not start) or oil separator, etc (as one person in this thread has noted - he mentioned his code pointed toward the o2 sensors but the actual problem was different).

Any ideas? Should I go ahead and change the pre-cat o2 sensors or is there any way to tell the exact problem before going ahead and purchasing parts?

I found great relief in this thread when I was working on a rough idle problem.

http://forum.e46fanatics.com/showthread.php?t=342081

Your symptoms sound a bit different but it doesnt hurt to get the adjuster unit cleaned up even if it doesn't turn out to be the cause...

Also, I am not sure if you've checked out the intake boot for possible cracks (or more like gapping holes if your car stalls frequently). Also, I am gonna assum that you have checked the possibility of a vacuum leak somewhere.

Lastly, and although the codes are pointing towards O2 sensors, that would be my last and final resort but only due to the fact that those suckers are fairly pricey...

Godd luck!

The problem is I can't even get the engine started. Can o2 sensors cause the engine to not start? I heard the most likely cause is the intake camshaft sensor but I've already replaced that and the engine still doesn't start. I'm now wondering what to do next - o2 sensors if it is possible that it is the cause

Originally Posted by charles_316

The problem is I can't even get the engine started. Can o2 sensors cause the engine to not start? I heard the most likely cause is the intake camshaft sensor but I've already replaced that and the engine still doesn't start. I'm now wondering what to do next - o2 sensors if it is possible that it is the cause

I highly doubt that O2 sensors and regardless of how bad they are will prevent the engine from starting. It might idle rough, it might run inefficiently (waste a lot of gas) but if all you've got are fouled sensors, it will run.

In fact, you could probably disconnect the sensor plugs and it should still start.

Is it not cranking or does it turn but doesn't start?

It is turning but not starting.

I actually have two more fault codes from the Peake tool - 2761 (secondary air system) and 2774 (engine cut off time). They don't have very good descriptions so I will have to Google this.

Thanks for this DIY, did a successful install this morning! FYI I went to auto zone to get the O2 sensor socket and ending being able to rent it and when I return it get my money back! good deal, atleast in LA!

Just wondering if anyone had new issues about their check engine light. My Peake tool just game me this reading:

Table 19:

E4 - O2 sensor adaptation limit Cyl # 4-6
E3 - O2 senor adaptation limit Cyl # 1-3
C6 - Catalytic convertor efficiency Cyl 1-3
CA - O2 sensor control limit Cyl 1-3
O6 - Fuel injector cyl # 1-3

I know that sometimes by fixing one thing can eliminate the other problems. I changed my spark plugs 6 months ago but never changed my spark plug booth. I was wondering if that has something to do with these codes. What advice can you guys share with me... Thanks

Worked like a charm and definitely a DIY, thanks for the write-up and pics!!! My buddy and I did this in about 30 mins. Make sure you have the socket for the 02 sensor. VERY VERY noticable performance improvement right away. I've got a 2001 330i with 124,000 and love her.. Peace!

After reading your write-up, I figured that I could give this a shot myself. I relpaced all four O2 Sensors and it was easy.

The hardest part was figuring out how to thread the post cat sensor wires between the engine bay and the exhaust. After several attempts I found a way to just drop them through in just the right place.

Thanks for the write up and visuals. My two front O2 sensors just took a crap too and my car is getting horrible gas milage and backfiring when cold. Time to save some money and print out your tutorial. Thanks again!

Great writeup

Thanks!! I'll be doing this very soon!

I'm getting:
P0313
P0300
P0155
P0154
P1348
P1350

Its possible or I'm hopeful that the P0154 and P0155 will go away after replacing the two pre-cat O2s... and I suspect that the misfire codes may be a result of the O2 sensor failure. Maybe wishful thinking on my part. I'll report what I get after I replace these bank 2 O2 sensors.

Thanks again!

Subscribed.