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Thread: 528 M52 Oxygen sensor removal

  1. #1
    Join Date
    Jul 2010
    Location
    Hawthorn Woods, IL.
    Posts
    14
    My Cars
    2012 328 turbo

    528 M52 Oxygen sensor removal

    This is my first post on a repair I just completed. I was frustrated that I couldn't find anything anywhere on the post-cat sensors. There are a few decent videos that cover the pre-cat removal process and are pretty easy to find. I'll briefly cover the same. I wanted to share the post-cat removal experience. Here goes.............

    I have a 1999 528it sportwagon with the M52 engine
    parts: 2 pre-cat Bosch 13477 available for $46.44 on Amazon
    2 post-cat Bosch 15109 available after various discounts from Advance
    Auto parts for $47.19

    Lisle O2 sensor socket $8.85
    Powerbuilt 648691 O2 sensor offset wrench $7.85

    Pre-cat removal & Installation is very easy using the Lisle o2 sensor socket with slot for harness. Both sensors are located on the passenger side of the engine and are very easy to see and remove. There are several videos on YouTube that cover this simple removal. Spray some liquid wrench or equivalent to help loosen the hold of the sensor. As you can see, the post cat sensors were extremely dirty.



    Remove the passenger side cabin air filter along with the hose entering the firewall for clearance. You will need to remove both plastic engine covers on top of the engine. Both have small plastic plugs covering the bolts. The one covering the oil filter helps give a little more clearance at the back corner of the engine. The middle one covers the post cat electrical connectors and are accessible here.











    Once you have most of these parts out of the way, it's a little easier to move around. If you are just doing the pre-cat sensors, you really don't have to remove the above parts. Most will do this whole job at once, so It's best to just get everything removed, then start with the pre-cat sensors.




    Slide the connector from the harness clip. You will see a cage clip on the end closest to the sensor. Remove it with a small screwdriver by prying up on the tabs. Take a medium size screwdriver and use it as a wedge to separate the two parts. Don't try to raise the clips with a screwdriver, as they will probably break. Using a screwdriver to twist and separate the two connectors- works much better. No clips broken.











    Post cat removal is much more difficult. The sensors are obstructed from view by the exhaust downpipes and located on top of them on the passenger side of the engine. They are pointed straight up, so getting them loose can be difficult. The pipe closer to the middle of the car is the easier of the two.




    This area is tough to get your hand in and can be quite frustrating. Go slow and take your time. I have a size large hand and it was tight, but doable. I can't imagine having an XL hand size work in such a tight space.





    Remove front passenger tire, use a large floor jack and jack the car high enough to crawl under. Fit the Lisle socket from under the car. Use 3/8 " drive extensions taped together with electrical tape to reach the socket . From the top of the engine, thread the extension down to the socket and turn until it engages the socket. Use an adapter socket (3/8 to 1/2) at the top to use a 1/2" drive breaker bar. You need the breaker bar to gain enough torque to break the grip of the sensor.



    The other pipe (outer pipe, closest to the right side tire) is more difficult because you cannot get an extension or swivel to fit in the Lisle socket because of the limited clearance of the wheel well. It is possible to fit the socket, but you can't get an extension fitted because of the limited clearance. If the hole in the downpipe would have been designed one inch further straight up, none of this would be an issue. Anyway, use the Powerbuilt 22mm (7/8) O2 sensor wrench. The offset square is now able to accept an extension from up top. You will also need an angle extension to clear the wheelwell. Again, the breaker bar will give you enough leverage to break the hold of the sensor. Any attempts to use the wrench from below were futile, there is no room to turn a wrench or use the offset wrench. It was much easier to reach from up top, although still a PITA. Your best bet is to have someone assist you in lining up the angle extension with the socket extension from above. One person below the car helping to guide the extension. Fit the wrench to the O2 sensor first and then guide the extension in.

    There is a zip tie that needs to be cut at the top of the engine. Replace one sensor at a time and take the new O2 sensor and lower it down from the back of the engine being careful to follow the original path down. You will notice the connectors to the post cat sensor are female ones as opposed to the male connectors attached to the pre-cat sensors. The post cat sensors have much longer harnesses to be able to reach the exhaust downpipes.

    The sensors are difficult to thread since they are on top of the pipes and the long harness resists coiling. Reverse twist the harness several turns and be patient, eventually it will thread and take hold. There are two different clips near the bottom of the engine that need to be opened for harness removal and re-assembly. Once you've tightened the sensors (same method as removal) , finish replacing the clips which keep the harness away from the engine.



    The pre-cat sensors took about 30 minutes total. The post-cat sensors kept me busy for a much longer time, as I wasted a lot of time trying to determine the best way to remove them. I finished this same job on a buddy's car in two hours total with his help. Doing this solo will take four hours and a lot more frustration. Give it a shot, it's nowhere near as bad or as difficult as it first looks.
    Last edited by Chazmo528; 12-21-2011 at 05:57 PM. Reason: adding photos

  2. #2
    Join Date
    Aug 2007
    Location
    USA
    Posts
    2,208
    My Cars
    (OO=[][]=OO)
    This is M52TU engine. M52 up to 9/1998 have a different sensor location.

  3. #3
    Join Date
    Jan 2012
    Location
    Finland
    Posts
    44
    My Cars
    2000 528i
    This is great! Good pictures
    e39 528i M - Sport -oo

  4. #4
    Join Date
    Jan 2008
    Location
    London.uk
    Posts
    158
    My Cars
    528i touring.
    Quote Originally Posted by joako View Post
    This is M52TU engine. M52 up to 9/1998 have a different sensor location.
    If possible is there a picture showing the location of the sensors on the M52b28 engine.

  5. #5
    Join Date
    Apr 2013
    Location
    Kensington, Maryland, USA
    Posts
    40
    My Cars
    528i E39;M52TUB28;5L40-E
    Thanks for posting Chaz.

    I guess you've moved on to a newer car, but currently this is a daily driver for me. As you may know, the pictures are no longer visible. If you have them, I am sure we'd appreciate you re-uploading them. All I am trying to know which post-car sensor is located where. (There is one bank 1 or 2 post-car near the front, and the other is closer to the firewall.)

    I guess I can remove the zip tie and deduce from that which one is which. If anyone knows please post.

    [edit 1: the o2 connector nearer to the front connects to the inside exhaust bank]
    [edit 2 (post repair): "From the top of the engine, thread the extension down to the socket and turn until it engages the socket. This was brilliant. I guess it is obvious to others but I was about to try from the bottom using a wrench extender, and it would have been a hassle since under the car let's be real you don't have much strength.

    The only lingering question for me was about these zip ties and wire paths---I tried a lot of wiring paths for the o2 sensors and the thick wire harness going into the ecu, but it wasn't clear what path was the best to avoid things like the covers crimping any of the o2 wires, the vacuum line for the secondary air pump, and thick wire bundle. Despite my efforts there's a smell of burning plastic upon test driving. I cannot locate the exact source though.]
    Last edited by jasontaylor7; 10-22-2023 at 10:35 AM.

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