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BMW and MINI DIY Video – Replacing Oxygen Sensors, O2, OBD-II, How To

February 2, 2015

The Bavarian Autosport Ultimate Maintenance Schedule (blog.bavauto.com/go/maintenance) is invaluable for BMW and MINI owners who wish to do all they can to keep their Ultimate Driving machines in top shape. At BavAuto, we have been working on completing sample DIY videos for each of the maintenance tasks listed on the Ultimate Maintenance Schedule. In this DIY video we will show a common oxygen sensor replacement.

BMWs and MINIs have two basic styles of oxygen sensor locations. The early BMW models, through 1995 have one sensor (two for V8s) mounted just ahead of the catalytic converter (one for each side, on V8 models). These sensors are generally accessed from under the car. Some models allow access from under the hood, as shown on a 1989 325is in the photo DIY article in the Fall 2004 issue of Fast Times (click HERE to see the article). Models produced for model year 1996 and later, must comply with the OBD-II (On Board Diagnostics v-2) mandates and have sensors mounted ahead of the catalytic converter(s) as well as behind the converter(s). Additionally, there will be a pair of before and after converter sensors for each “bank” of cylinders. 6-cylinders, V8s, V10s and V12s have 2 banks and, therefore, 2 before-converter and 2 after-converter sensors. 4-cylinders have 1 bank and just one before and one after-converter sensor.

In this DIY, we will address a typical OBD-II (1996-on) oxygen sensor replacement. We will be showing the very common M54 6-cylinder engine as used in the 3, 5, Z and X models from the 2000s. The before-converter sensors are accessed from under the hood and the after-converter sensors are accessed from under the vehicle. Earlier OBD-II models and V8/V10 models may require access to all sensors from under the vehicle.

Click image below for oxygen sensors:


Click below for oxygen sensor removal tools:

Click below for MechanicAll penetrant:


Bentley repair manuals:

PROCEDURE:

Under-hood access to before-converter sensors:

1) Locate the before converter sensors on the passenger side of the engine, just outboard and below the valve cover (M54 6-cylinder shown in this example).

2) To remove and install the sensors, we’ll use the socket style oxygen sensor tool (BavAuto.com), a 3/8” to ½” drive adapter, ½” drive extension and a ½” drive ratchet.

NOTE: Oxygen sensors can be rusted into place. Working on them when they are warm (from the engine running) can help with removal. Be careful of hot engine and exhaust parts if working on a hot engine. Application of a good penetrant, such as the MechanicAll (BavAuto.com) may assist in successful sensor removal.

3) Follow the wiring harness from the sensor to the harness-to-vehicle plug. Disconnect the sensor harness plug from the vehicle harness plug. Release any ties or clips securing the sensor’s harness to the engine or vehicle.

4) Slide the cut-out in the side of the socket over the sensor’s wiring harness and secure the socket onto the Sensor’s hex base.

5) Apply torque to the ratchet to loosen and then unscrew and remove the sensor.

6) Install the new sensor being careful to not touch the sensor’s end. Note that there is a pre-applied anti-seize compound of the sensor’s threads.

7) Tighten the sensor to the specified torque (available in the applicable Bentley repair manual). In this case, the torque is 37 ft-lbs.

8) Route the sensor’s harness through any ties or clips and connect to the vehicle harness plug.

9) Repeat 3 through 8 for the other before-converter sensor.


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6 Comments
  1. NickS permalink

    Thanks for another excellent video tutorial, Otto.

    I have a 2000 BMW 328i with approximately 160,000 miles on the clock. I’ve owned it for approximately 60k miles, and am unsure whether the O2 sensors have ever been changed.

    How does one know replacing the O2 sensors is necessary? Will an OBD-II code be thrown if they are failing/worn out, or will certain symptoms turn up?

    Is replacing the sensors something that is good to do periodically and proactively, along the lines of changing the oil, or best to leave alone until necessary?

    • Well, if we were to assume that the sensors may not have been replaced at 100,000 miles, when you purchased the car, at 160,000 miles, the sensors will certainly be in a degraded mode. They may still not be bad enough to generate an engine management fault code, but replacement would likely net a gain in fuel economy and maybe even better throttle response. Technically, they are still within parameters if there are no fault codes being generated that would point to the sensors.

  2. Greg C permalink

    On my 2005 325i with M-56 engine (SULEV) it occasionally throws a code that O2 Sensor signals swapped bank 1 bank 2 (?) The vehicle has done this since I bought it with 22,000 miles on it. BMW did not correct the problem. Now the engine has a ‘stutter problem’ around 2800 RPM to 4000 RPM under a load. I have replaced the DISA unit. The vehicle now has 63,000 miles on it. Suggestions? Could this be lazy pre cat O2 sensor(s)?

    Thank you in advance!

    Greg

    • Greg,
      What is the actual fault code for the “swapped sensors”? Do you have it as a universal “P” code?

  3. Rob Gibson permalink

    I really liked this video but the index said it also dealt with an R56 Mini Cooper.
    I saw no references to a Mini. Is that a different video?

    • We do not have a MINI specific video yet. This video can be used in a general way as far as the general steps on replacing O2 sensors on various models. The Bentley repair manual for the MINIs would cover the model specific steps.
      Bentley Manual:
      https://www.bavauto.com/fland.asp?part=bm13

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