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Pelican Technical Article:

E30 3-Series Oxygen Sensor
Replacement
Jared Fenton
jared@pelicanparts.com

Difficulty Level: 3
Difficulty scale: Adding air to your tires is level one
Rebuilding a BMW Motor is level ten

     This article is the one in a series that will be released in conjunction with Wayne's upcoming book, 101 Projects for Your BMW 3-Series.  The book will be 256 pages of full color projects detailing everything from performance mods to timing the camshafts.   With more than 350+ full-color glossy photos accompanying extensive step-by-step procedures, this book should be a staple in any 3-Series owner's collection.  See The Official Book Website for more details.  The book is due out in October 2005.  

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Figure 11


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Figure 13

 

 

     In this tech article, we will discuss replacement of the oxygen sensor in 1984-91 E30 3 Series BMW cars. While this article displays replacement of the sensor on my 325is, it should be noted that this article applies to most other fuel injected BMW models as well.

     Why replace your oxygen (or O2) sensor? It is an essential part of maintenance on your BMW. The O2 sensor is used to monitor the fuel-air mixture of the car and send vital information to the car’s on-board computer (OBC), which in turn adjusts the mixture and timing of the car. It does this by measuring the oxygen content of the exhaust. Over time, O2 sensors wear out, due to heat and carbon buildup from the exhaust. When the O2 sensor begins to wear out, you may notice the car runs a bit sluggish, fuel economy may be down, and in sometimes, it may cause an annoying intermittent surging idle problem, (as was the case on my car). Once I replaced the O2 sensor, I noticed a increase in gas mileage as well as a mid-range increase in power and drivability.

     BMW recommends that the O2 sensor be replaced every 60,000 miles. This article is written with the home mechanic in mind. With a few tools and the correct parts, you will be able to replace the sensor yourself.

     The first step of this article is to disconnect the battery. You will want to do this anytime you are working with electrical components. Plugging an electrical component into the electrical system with the battery connected can cause a voltage spike. Voltage spikes can destroy your OBC. That said, let’s begin.

     Open the hood and look down on the passenger side of the engine, you will see the exhaust manifold. Now, if you follow this down a bit, you will see a small sensor threaded into the side of the manifold. This is what we are replacing (Figure 1).

     You will want to locate the electrical connector that the O2 sensor plugs into. On my 325is, this is located under the panel shown in the photo, right behind the front passenger side shock tower. Look at the top near the shock mount. You will notice a small plastic clip, holding the connector under the panel (Figure 2). You will want to rotate this clip 90 degrees, so the pin on the side lines up with the indexed hole, then use a screwdriver to carefully push the sides of the clip in. Once you have the sides of the clip pushed in, it should simply drop through the panel (Figure 3).  With the connector free, you will want to remove the wire harness from the two clips shown in this picture (Figure 4)

     Once you have the connector free, you will notice it has a screw-type collar, as shown here in Figure 5.  Unscrew this collar, and pull the O2 sensor plug out of the connector (Figure 6).

     Next, you will want to remove the small heat shield around the O2 sensor, this simply pulls off (Figure 7 and Figure 8). Remove the wiring harness from the clip as well. Now you will see the nut around the O2 sensor.

     With the engine cold, spray a good penetrant spray (such as WD40 or 3 in 1 oil) around the O2 sensor where it plugs into the manifold. This will prevent the sensor from stripping out the threads when removing it. Let the penetrant soak for a few hours before continuing. Now is a good time to grab a beer or fruit juice, depending on your taste, of course.

     Once the spray has worked itself into the threads, it is time to remove it. There are some tools on the market such as this O2 sensor removal socket that will assist in the removal of the sensor, however I found there was not enough clearance to use it (Figure 9).  I recommend using the O2 sensor removal socket whenever possible.  In this instance, I used a large pair of vice-grips around the nut to loosen the sensor. Simply reach down into the engine bay, use the vice-grips around the sensor and give it a few strong tugs. It should loosen up. Be cautious to avoid stripping out the threads (Figure 10).

     When the sensor is loose, remove the vice-grips, and thread out the sensor by hand. Once I removed my the old sensor, I noticed that there was some carbon buildup on the sensor face, indicating that the car had been running rich for a while (Figure 11).  The new sensor should correct this problem.

     Now that the old sensor has been removed, it’s a good idea to spray a little bit of the penetrant spray on the inside of the threads inside the exhaust manifold. This will clean up any rust and soot that may have built up. Usually a quick little spray and then a few wipes with a rag will suffice.

     Look at the new sensor (Figure 12).    You will see a protective plastic cap over the tip that fits into the exhaust manifold. This is the part that actually senses oxygen in the system. It is crucial that you keep this tip clean. You will also notice a bit of anti-seize compound on the side of the sensor’s threads. DO NOT allow any of this to get on the tip. It will damage the sensor (Figure 13 - shown with plastic protective cap).

     Now remove the protective cap, and carefully thread it into the manifold, making sure not to get any of the anti-seize compound on the tip. Hand tighten the sensor until it stops. Use the vice-grips around the outside nut to tighten it. BMW recommends that the O2 sensor be torqued to 55ft/lbs., however since I cant fit a torque wrench on there, I got it as tight as I possibly could when cold, then re-tightened the sensor with the engine and exhaust hot. This should secure the sensor in place.

     With the new sensor installed and tightened, place the protective heat shield back around the sensor, and clip the wire in place. Next, plug the sensor’s plug back into the connector above, slide the threaded collar around the outside and hand tighten.

     Once the sensor is plugged into the connector, line up the securing clip under the panel behind the shock mount. Line up the pin, then rotate it 90 degrees for the boss to slide through the panel. Once it is through the panel, rotate the clip 90 degrees to lock it in place.

And that’s it, you’re done!

If anyone has any questions regarding installation feel free to email me at jared@pelicanparts.com

Cheers!

Jared Fenton

This technical article is made possible solely through the support of Pelican Parts.  If you like what you see here, then please visit our online BMW catalog and help support the collection and creating of new and informative technical articles like this one.

Comments and Suggestions:
mym3Comments: I have e30 m3. This is second time i have changed O2 sensor.I use a 7/8 wrench i cut in half.You can use either end open or box.Just use some muscle or small pry bar
May 6, 2012
fairly intelligent personComments: Use a torch to heat the bung the o2 sensor threads into if you are having difficulty removing it....I.E. it is seized.....don't be a jerk & put visegrips on it...use a 22mm wrench or the appropriate tool if you want to avoid a mechanic....anyways don't drive a bmw if you cannot afford to maintain it in the 1st place....buy a kia
February 4, 2012
RayComments: my bmw 316i 1997 model started to raise idling to 1 on the the rave counter sometimes even more than 1 .ln the mornings when its cold l start it and it just turn off until when the engine is warm what could be the problem?
December 5, 2011
GabeComments: i just ordered an O2 sensor for my 95 318is from the local autozone. looking at the picture, i think that it only has two wires, whilst mine has four. will i be able to use the two-wire sensor, or will i have to return it for a four-wire one?
December 2, 2011
 Followup from the Pelican Staff: The four wire ones have a pre-heater in them. If you use the two-wire one instead, you will probably trigger errors by the computer as it will think the heater circuit is dead. - Wayne at Pelican Parts
AsianSpankerComments: I really like it when Jared takes the time to post pictures of the subject! It shows that one extra bit of effort that makes him the go-to guy at Pelican. Whenever we see or hear something we don't like as customers we are never shy about complaining. Well, lets not be shy when we see someone put in a bit more effort! Hat's off to Jared for the the effort. I am sure Wayne will remember that when he gives raises!
September 6, 2011
ozzzoComments: I can't believe you are telling people to use vice-grips to remove the oxygen sensor. That is bad advice, because a non-zero number of people will read that, and then strip it so that a wrench won't fit, and after it strips they will tighten up the vice-grips until they crush it, and then it will never come out and they will replace the exhaust manifold. Vice-grips can turn this 15-minute job into a multi-day project. Please don't ever put vice-grips on any nut or bolt unless it is already hopelessly stripped.

Here is the correct solution if you don't have the special socket, or it doesn't fit. Unplug the sensor wire. Run the wire through the hole of an open-end wrench, and then fit the wrench over the sensor and remove it. If you can't turn the wrench, get a longer one, or hook another wrench on the end for leverage do not try this with cheap wrenches because they may break.
July 3, 2011
redtwinComments: Hi, can someone tell me the O2 sensor wiring detail. My connector got ripped out and am hard wiring the sensor to the 4 cables. but the wire colors at the sensor end is different from the car end of the cable. Which color cables at the sensor end go to which colors at the other end?
October 26, 2010
 Followup from the Pelican Staff: There should be two wires for the heater and two wires for the signal. I don't think those are polarized, so you can swap the two wires to the heater and the two to the sensor without any ill effects. But you have to have the right wires going to the right components (heater or sensor). You can use a multi-tester and see if you can find a voltage going to the heater, that should give you a hint. - Wayne at Pelican Parts
alexComments: i replaced my O2 sensor today and i don't really notice any difference. my car has been kind of sputtering, sluggish, and has low rpm speeds.

since it was rather difficult to get the O2 sensor in to it's proper place, i might have gotten some of the compound on it. is it worth me taking off and cleaning it with something? and if so, how should i clean it?
October 23, 2010
 Followup from the Pelican Staff: If replacing the O2 sensor really didn't help, then it's most likely not the problem. I doubt that you could have gotten too much of the anti-seize on the sensor cover. - Wayne at Pelican Parts
rikarenaComments: MY 1990 750il. speed don't encrace when I step on gas pedal
June 22, 2010
 Followup from the Pelican Staff: I would pull the codes and see what the engine is telling you: http://www.pelicanparts.com/bmw/techarticles/Mult-Code_Reading/Mult-Code_Reading.htm - Wayne at Pelican Parts
pure n coolComments: this happens at around 30 kph and goes away once i accelerate.
June 8, 2010
Pure n coolComments: I have a automatic 320iE30, I keep getting a slight shudder from the back but there does not appear to be anything wrong with the diff. Any ideas on what could be wrong??
June 8, 2010
 Followup from the Pelican Staff: Tough to say - that's nearly impossible to diagnose over the Internet. - Wayne at Pelican Parts
EgnaledknarfComments: The socket in picture 9 is not a lambda/O2 sensor socket... it is a shock absorber or spindle joint removal socket. The opening in the side is there to allow access to the hex/torx on top of the shock absorber or spindle joint. A lambda/O2 sensor socket has an opening all the way down to the bottom so the cable can remain attached. A picture of a real deep lambda/O2 socket is attached.
May 27, 2010
 Followup from the Pelican Staff: I've used both to remove O2 sensors - just different ways to slice the bread. On most O2 sensors, the connector will fit through the hole in the tool listed in the article. On some cars it won't. Most times a 22mm open wrench will work fine too, depending upon access. - Wayne at Pelican Parts 
RandyComments: I have a 325i Convertible that was manufactured in 12/86, so my oxygen sensor is slightly different from the one in your example plug in verses screw on with threads. Figures 5,6 & 12. Any words of wisdom getting the old one unplugged because I'm having some difficulty and I don't want to break it.
March 9, 2010
qtysonComments: Honestly, I'm having a hard time finding the Bank 1 & 2 sensor 1's-o2 sensors on my 98 528i. The pics are good but a little confusing from certain points of view. Close-up great but medium shots to close-ups would do a lot more good. Because my 528i ain't easy looking like a 3 series.
January 1, 2010
steveComments: I need to replace the oxygen sensors on my BMW 33i conv. Which sensors do I need? The ones for before or after the catalytic converter and how many doI need?
December 24, 2009
Adi BComments: Hi, I have a 328i conv. 1997 and with my code reader I got two codes E9.Catalyst efficiency below threshold Cyl #1-3 and EA.Catalyst efficiency below threshold Cyl #4-6. I was able to reset the alarm with the Reset Tool Face. What shoud I do next to prevent any damages in the future ?.could you help me thanks
October 2, 2009
 Followup from the Pelican Staff: It may be that your secondary (behind the cat) O2 sensors need replacing, or your catalytic converters need to be replaced. Now that you have reset the codes, I would keep an eye on it and see if they reappear. - Wayne at Pelican Parts
tellComments: when engine is cold will start but within 20 seconds it will flood with petrol and will run as if it was firing on 2 cylinders and will cut out and will not start take pulgs out dry them and fire the car up when starts runs really rich and lumpie and reving it until it clear it felt if choke was out and is getting to much fuel once engine is warm it is ok any suggestions? would it be the 02 sensor

September 2, 2009
 Followup from the Pelican Staff: If that is happening, then it sounds like you have a clogged injector. The car should never flood with gas under any circumstance, unless the injectors are clogged and stuck open. - Wayne at Pelican Parts
jonathandComments: hi, I'm driving e30 320i 89 model black bumper and i am battling to sort out my cold start problem. i bought two new sensors the coolant sensor blue one and the grey one and did fit on my thermostat housing. when i start and both attached it takes ages to start but if i unplug the blue one it starts immediately. i then bought two of the blue plugs still has a problem..any suggestion you might have.
August 23, 2009
 Followup from the Pelican Staff: Hmm, I would check the sensors for the proper values and also check the wire harness. Sorry, it's difficult to diagnose things from afar. - Wayne at Pelican Parts
DiehardComments: hi, i am driving a 320i E30 and i am trying to locate my oxygen sensor but cannot find it..i checked on my exhaust and i cant find it..pls help
August 23, 2009
 Followup from the Pelican Staff: Hi there. The O2 sensor wasn't used on all cars, some Euro models didn't use one. I suspect that your car may be one of those? - Wayne at Pelican Parts
TimComments: i just got mine out... been attempting for months, finally did it right. You have to put the PB Blaster penetrant on it quite thoroughly and let it sit for a few hours. I then put more on and waited another hour, then I was golden. A pair of vice grips and some muscle and it slowly unscrewed. Good luck!
August 14, 2009
vonComments: how do you removed it if it's ceased on there? I can't get mine off.
May 9, 2009
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