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BMW DIY Replacing On-Board Computer (OBC) Illumination Lights E34 and E32

September 28, 2009

The OBC [on-board computer] light on my ‘91 525i just went out. I think you did a write-up on replacing the OBC light bar some time ago. If I remember, it was a pretty simple fix. My problem is I can’t find the article or the replacement light bar on your web site. Can you help me out?

The article you’re referring to was in the Spring 2004 issue of Fast Times.  The reason you can’t find the light bar for your car is that it doesn’t use one. Instead, your OBC uses three individual bulbs to illuminate it. The E34 5-series (89-96 525i, 525it, 530i, 530it, 535i, 540i, M5) and E32 7-series (88-94 735i, 735il, 740i, 740il, 750il) use the same OBC design.  You can access the illumination bulbs by removing the radio and then the OBC itself.

1)  Remove the radio.  Original BMW radio is removed by loosening the two securing screws under the small hinged flaps at the left and right sides of the radio, then pulling the radio out.

2)  Once the radio is out, pull the release lever in the right rear corner of the radio cavity and pull the OBC out.

3)  Once the OBC has been removed, you can simply replace the defective bulb(s).

The part number for the bulbs is 2721S (three required).  Note that this part number is different from what BMW says is used.  In this case the BMW “micro-film” parts look-up is incorrect.  The BMW part number is a 6-volt bulb.  The OBC needs 12-volt bulbs.  The 6-volt bulbs burn out quickly.

2721S OBC bulbs:

Radio removal tool:

  1. Hi
    I’m trying to replace the OBC bulb on my 95 525i. I received the part from you (part# 65811374495 Bulb With Socket). I pulled out the radio but I don’t see where the release lever is to pull the OBC out. Please adivse on how to pull the OBC out and change the bulb. Thanks!

    • The release lever for the OBC is at the rear of the OBC, through the radio mounting cavity. As I recall, the lever is gray or green. You pull the lever forward. We do not currently have an E34 chassis here, but we do have access to a couple. We can take some photos for you and post them up.

      There is a photo of the lever (with the OBC already removed) in the Bentley repair manual for the E34 chassis, on page 620-6.

      BMW E34 OBC removal

      Illustration from BMW 5 Series (E34) Repair Manual: 1989-1995, © 1998, published by

      Click here for Bentley repair manuals:

  2. K A Robinson permalink

    Still can’t see the release lever. could you provide photos. I even went in from the glove compartment side. No luck

    • Did you look at the photo in the Bentley repair manual, that I had mentioned previously?

  3. K A Robinson permalink

    Ok, tried again this time with sucess. Actually my spouse stuck her hand in the opening and found the tab, and with a little more pressure which we thought was a lot the unit came flying out. Thanks.

    • Yes, it does take a pretty good tug on the lever. Thank you for the follow-up!

  4. 95525i permalink

    ok, so my 95 525i was making some weird noise like my heater was about to explode,not the best idea but i was kind of angry so i started hitting the side where the obc is and where the swtich to control the heat a/c is, i gave it a few minor hits and the noise stopped, but as the noise stopped so did my on board computer, all the lights quit working except for at night it works like a charm all bright and nice.. Otto you think i messed the wiring up or did i just blow a bulb smacking the side of it? id just like to know if i just need a new bulb or a whole new obc for my bmw id ratrher not touch it till i know


    • At this point, we would recommend removing the OBC and replacing the bulbs (as noted in the original posting). Let’s see what this gives you.

  5. Dave permalink

    I have a 1991 325i. The lights are out on my OBC. I found OBC’s online for around $50. Is it worth it to just buy a new one or is replacing the lights the way to go?

    Also, How do I remove the dash cover to get to the radio?

    • Otto permalink

      With the cost of new bulbs just being a few dollars, we would not see any real benefit in replacing the whole OBC unit, unless the unit itself is faulty.

      The radio is easily removed by loosening the two securing screws, located under the hinged covers at the left and right edges of the radio. Use the special radio tool to loosen the screws, then just pull the radio out.

      Click HERE for radio removal tool

  6. Mark Peterson permalink


    I found this website yesterday after searching and reading several other sites on how to remove and replace the OBC. This was the jackpot! I have a 1994 530i BMW and even my BMW mechanic was a little hazy on the exact R&R for my model. He told me to remove radio but thought the OBC came out the back; as some do. I was about ready to live without the OBC, which is mostly a clock.

    A couple of comments which might help some one. The “tug” on that lever, is tough. I can’t believe that guy’s wife did it. I kept thinking the lever would break and I used a screwdriver from the front to carefully pry a little as I tugged at the lever. I did’t realize the bulbs(3) turn 90 degrees to remove and same to replace. Also make sure the lever is in forward position when replacing the OBC.

    The bulbs were $6.50 a piece! This was a fun now easy project and thanks for your help. Reading about having to go through the glove compartment and removing the dash board gave me ulcers. I could see deploying the air bag or freezing the engine for good just to have my clock fixed.

    Thanks again

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