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Dashboard batteries

Discussion in 'E30 (1984-1993)' started by guderian, Jun 7, 2008.

    • Member

    guderian

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    Question : Has anyone ever simply removed the service indicator batteries and left them removed? Does the open circuit affect anything? I have removed the service lights long ago and am now experiencing temp gauge malfunction and some erratic dashboard lights.
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    Brian A

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    SI board does more than just Service Indicate

    The Service Indicator board does a lot more than just keep track of when then next service is needed. It is very likely that a lot of stuff would not work without the SI batteries; the car may not even run. I know the SI board battery condition affects the gauges and also stores any "fault codes" the diagnostics pick up.

    I've got my SI LED bank removed too, which I prefer since I do service work based on mileage and /or time and don't care if the car calculates green, yellow or red. Based on my experience, I really don't think that removing the LEDs has caused the problems you're having. The temperture gauge problem can be caused by weak SI board batteries (my temp guage gets jumpy when my SI board batteries are weak), but I doubt the dash light problem is SI board related.

    I've heard of replacement SI Boards which do not have batteries. Presumably they have modern capacitors or flash memory to do the things the batteries needed to do. I've not used one, in fact, I still have my original board (with 2 AA size batteries) except I've moved the batteries off the board and relocated them under the dashboard so that I can change them without taking apart the dashboard.

    Vicksburg guest

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    Man, what are these batteries?......do I need them in a 1988 325ic? How do I know if they are working? How do I get to them if they have to be changed? Damn, this sucks......AA batteries buried in the dashboard making the car run?!!!
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    guderian

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    These batteries are a pair of nicads hardwired (ie , soldered) into the dashboard circuit locared right behind the indicator panel. They are a design goof in that nicads last about 10 years max and bmw will not risk (my dealer won't) unsoldering these batteries and replacing batteries only - the whole indicator board is replaced. Sometimes they leak and destroy circuitry. Mostly they just die and faults are no longer stored and indicator lights do not go on. What I don't know is what exactly else these batteries do in terms of car computor gimmickry - there is more fear factor than knowledge at my dealer's ('they must be replaced...car won't run...very complex circuitry...'). I am waiting to hear from someone who has taken them and thrown them away. Mine are 24 years old and simply can't be working although the car runs fine.
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    Brian A

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    Yeah, it's a pain that there are a couple of AA batteries buried deep in the dash. I think its attributable to 1980s technology. Now we have modern "flash memory" and other better solutions, BMW would not have put in batteries like that. The batteries are there so that the car does not lose maintenance/diagnostic information when the main battery is disconnected.

    The Service Indicator board IS a little mysterious as to all the things it does. Hopefully some other techie poster can detail it out. It obviously runs the Service Indicator LEDs (the green, yellow, red things) by doing calculations using mileage, RPM, temperature etc to calculate when service is due. Again, by modern standards, its not very sophisticated and most people use time and mileage to guide service intervals (especially since virtually all E30s are now well above 100,000 miles anyway).

    The SI Board also stores the "Fault Codes" that the on-board diagnostic systems capture. These codes are read by plugging a tool into that old fashioned 3" diameter socket in the engine compartment or by counting Morse code style blinks on the dash board.

    Last, the SI board seems to affect the instrument panel gauges. If the batteries are weak, some gauges get jumpy. For my car, first the MPG needle starts jumping in steps rather than moving smoothly, next the Engine Temperature gauge starts jumping around, next the Tachometer starts going wacky. I've never left the batteries beyond that.

    Last time I changed my batteries, my car had severe drivability issues. I was just changing the batteries to try to capture the Fault Codes. After I changed the batteries, the problem completely went away. I am not sure if I just fixed a loose connection in the process of changing the batteries or if the batteries themselves were the culprit.

    I doubt the car would run without the batteries in place. But then again, there are folks like "guderian", who experience no problems at all with 24 year old NiCds.

    Regarding solutions, here is a really interesting and cheap solution:
    http://stage.bmwcca.org/forum/showthread.php?p=7123#post7123

    I've done the fanciest solution:
    http://stage.bmwcca.org/forum/showthread.php?p=6392#post6392

    The other alternative is to buy a whole new board. I think new ones eliminate the batteries by using modern flash memory rather than requiring the board to hold its own voltage.

    Hope this helps.
    • Member

    az3579

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    Yep. The SI board stores all of this information and is powered by the SI batteries when power is removed. The car should run without the batteries as I once took my entire cluster out and drove to the local parts store without my instrument cluster installed. If the cluster's not installed, the batteries cannot be attached to the circuitry of the vehicle in any way.


    This may vary, who knows. What I do know is that the information isn't stored in the batteries; the batteries provide power to the circuitry on the board that stores this information. Once the batteries are moved, the power is lost to the circuitry and all service information is gone (e.g. Service Indicator lights).

    I have proven all of this with my experiences when fiddling with my instrument cluster and service indicator board. All of this is true for my car, at least.


    As Brian A said, things like the tachometer, temperature gauge, or the MPG gauge might act up if the batteries are going. At this point it would be wise to replace the batteries, but if you want to be on the safe side, I would replace the board and the batteries. This would eliminate any faults with either of those pieces of hardware. That's why I replaced both; I didn't want to go through the hassle and labor of replacing the batteries only to find out that it was actually my SI board that was defective.

    Vicksburg guest

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    Thanks for all the info. Any idea idea on the cost of the board + batteries?
    • Member

    az3579

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    Depends on where you get it. I got reeeeeeeeeeeally lucky and found my SI board WITH batteries on eBay for $79. Most of the time, a remanufactured one will go for over $150...


    ... it all depends. I'll take a look for you and see what I can find when I get home.

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