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Thread: Success in General Module Repair

  1. #26
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    also alarm/disable function. Cool Dog
    Last edited by shogun; 08-18-2021 at 09:06 AM.

  2. #27
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    GM rebuild

    Alarm disable function.I did my module ,everything else works now except
    my remotes and my alarm .Still can't disable alarm.I have to run with the DWS fuse pulled and my remotes won't work.Think it still might be the GM?

  3. #28
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    zebber500: Even though the A1 general module (GM) is related to those, your issue seems to lie elsewhere. Do you have access to a BMW DIS diagnostic system?

  4. #29
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    There could also be a problem with your Drivers' door module. Have you tried to unlock from the passenger side door? (Different module, both D & P modules send the signal to the DWS AFAIK)
    The reason I say that is because my car will sometimes not power unlock/disarm from the drivers door. It will mechanically unlock just fine, but not power unlock & disarm.
    Last edited by shogun; 08-18-2021 at 09:07 AM.

    '89 735i, '91 850i, '81 MB 380SLC (For Sale), Tesla Model 3, and VW Passat TDI -- Yes, I still repair General Modules, DM for info!

  5. #30
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    (please forgive the cross-post)
    Hey folks... I just repaired another GM and created a PDF with photos.
    EEDegreeToDrive's Ultimate GM Repair Doc
    Update:

    https://drive.google.com/open?id=1lF...6w1i9flrbtUFHm


    There isn't anything terribly new that Revtor, Spandrel and others haven't documented in the past, but I included my photos and tips, and added it to a PDF that can be downloaded/printed.

    Please take a look, and give me any feedback that you think it needs.
    I am planning to make it more complete and add the 2 GM removal processes, bad GM symptoms and failure explanations, and maybe some photos of GM repairs gone wrong (things not to do).

    Revtor: I borrowed your polarity image.
    Spandrel: May I borrow your knee bolster removal instructions/photos and credit you in the next version?
    Last edited by EEDegreeToDrive; 05-03-2020 at 04:42 PM. Reason: New file

    '89 735i, '91 850i, '81 MB 380SLC (For Sale), Tesla Model 3, and VW Passat TDI -- Yes, I still repair General Modules, DM for info!

  6. #31
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    GM rebuild

    The problem wasn't the GM, my MID shorted out, blew the #31 fuse and since the rearview mirror/remote receiver shares the fuse # 31 with the MID it apparently smoked the mirror.Which in turn would not let the remotes reset the alarm.A nice used mirror from Bluesman fixed the problem.Who would have thought?It took me 3 weeks to figure out.

  7. #32
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    All---
    Another forum member sent me his GM to repair. I used the opportunity to record my very first youtube video!
    [ame=http://youtu.be/qbfdIqzLc_0]The E31 GM capacitor repair VIDEO! [/ame]

    Feedback welcome, but forgive my 1-take dryness. I could have done it in 10 minutes if I had my diagonal cutters and wasn't fumbling with the camera...

    I still recommend reading:
    The PDF version of my GM Repair Guide

    '89 735i, '91 850i, '81 MB 380SLC (For Sale), Tesla Model 3, and VW Passat TDI -- Yes, I still repair General Modules, DM for info!

  8. #33
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    danieldd just pointed out a problem with my PDF instruction sheet. Apparently, the picture in the PDF picture shows the capacitors incorrectly as 100uF, 47uF, 10uF, 1uF and they should be in the following order.. 100uf, 47uF, 1uf, 10uf as per Revtor's drawing, the table at the beginning of the document, and my business card cheat-sheet I have used to repair other folks' boards.

    BTW the photo of the capacitors in the wrong order was my spare GM, and it was fixed.
    Thanks danieldd for pointing this out!
    Last edited by EEDegreeToDrive; 01-24-2013 at 10:07 PM.

    '89 735i, '91 850i, '81 MB 380SLC (For Sale), Tesla Model 3, and VW Passat TDI -- Yes, I still repair General Modules, DM for info!

  9. #34
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    Folks--
    I just received an order with more capacitors from Newark. For reference, here are the Newark.com part numbers:

    Main Capacitor: 14M6702 (Vishay 470uF, 40V Low ESR, 10000 hrs @ 105C, 12.5x30mm) ~$2.77/ea

    For the Smaller Capacitors, I am now using the brand Multicomp, they have a smaller footprint than the Vishay ones I used before and fit better. I also picked up a ~$30 bottle of conformal coating.
    97M3998 100uF 25V 105C 8x13mm ~$0.38
    97M3989 47uF 25V 105C 6x13mm ~$0.29
    97M4031 1uF 63V 105C 6x13mm ~$0.29
    97M4032 10uF 63V 105C 6x13mm ~$0.31

    EDIT: I have updated the PDF file with these latest part numbers

    Feel free to buy direct from Newark, but if you want, I can send out a kit of 5 caps for a reasonable price. I bought enough to supply a few other folks. I can ship out kits (5 caps) for $4/kit + $4 for shipping. If you want/need a set, send me a PM.
    If you don't want to risk damaging your GM and want me to do the work, send me a PM for more details. I'm certainly not trying to make a living on this, just making sure the E31 GM population survives and no more modules are mutilated with wrong parts/shoddy repairs. Also-- I perform local GM repairs (DC Metro/MD area) for beer and good company...

    ALSO, EXPERT OPINION NEEDED: I just cleaned the contacts in a member's relay module. I noticed that it too has some capacitors similar to the GM (Three 1uF and Two 10uF) so I replaced them, since they are likely the same age as the GM ones. Do you think these would adversely affect things if not replaced?
    Last edited by EEDegreeToDrive; 01-25-2013 at 12:55 AM.

    '89 735i, '91 850i, '81 MB 380SLC (For Sale), Tesla Model 3, and VW Passat TDI -- Yes, I still repair General Modules, DM for info!

  10. #35
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    Well it certainly cant hurt. I would.
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  11. #36
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    Quote Originally Posted by IcemanBHE View Post
    Well it certainly cant hurt. I would.
    Thanks, I was thinking the same-- I'm sure new RM caps won't hurt, just not sure if they will help anything.
    I suspect the only capacitors that are toast are the ones that have had ~12V on them for the last 20+ years.. Namely the main caps in the GM that have HOT-AT-ALL-TIMES power.
    I haven't seen/don't recall any problems that were resolved by RM capacitors, but the only sensitive parts on the RM are some combinational logic.

    Anyway, in Shogun style--
    Jeremy - One set of caps headed your way
    Jim - 4 sets headed your way + bonus inside
    Dan - 3 sets headed your way + bonus
    Mike- Your GM & RM are headed back your way, RM has new caps too. Let us know if the RM caps solve any mystery problems

    '89 735i, '91 850i, '81 MB 380SLC (For Sale), Tesla Model 3, and VW Passat TDI -- Yes, I still repair General Modules, DM for info!

  12. #37
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    I was just looking at your video before seeing this thread. Excellent video
    Last edited by shogun; 08-18-2021 at 09:08 AM.
    Matthew M.
    North Carolina, USA
    1997 840Ci | 2001 740iL | 1985 308GTSi Quattrovalvole

  13. #38
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    Quote Originally Posted by EEDegreeToDrive View Post
    I just cleaned the contacts in a member's relay module. I noticed that it too has some capacitors similar to the GM (Three 1uF and Two 10uF) so I replaced them, since they are likely the same age as the GM ones. Do you think these would adversely affect things if not replaced?
    Most of the A5 relay module (RM) failures seem to be either relays that broke over time or corrosion due to water ingress. All electrolytic capacitors in the RM have a voltage rating of 63 V which should be plenty for an application like this. I have never measured/tested the electrolytic capacitors from a bad general module, but I don't think the 1 and 10 µF (63 V) caps in the GM are the problem. That doesn't mean it's a bad idea to replace the capacitors in the RM as well, but with that attitude you will find yourself replacing a lot of electrolytic capacitors in the E31. Almost every module contains some, yet only one module is really notorious for it (although I think some of the instrument cluster failures may also be elco related)...
    Last edited by revtor; 01-25-2013 at 01:48 AM.

  14. #39
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    Quote Originally Posted by revtor View Post
    Most of the A5 relay module (RM) failures seem to be either relays that broke over time or corrosion due to water ingress. All electrolytic capacitors in the RM have a voltage rating of 63 V which should be plenty for an application like this. I have never measured/tested the electrolytic capacitors from a bad general module, but I don't think the 1 and 10 µF (63 V) caps in the GM are the problem. That doesn't mean it's a bad idea to replace the capacitors in the RM as well, but with that attitude you will find yourself replacing a lot of electrolytic capacitors in the E31. Almost every module contains some, yet only one module is really notorious for it (although I think some of the instrument cluster failures may also be elco related)...
    I agree-- Primary failures of the RM are likely the relays, as they are moving parts. The mechanical action can be compromised, but the arcing of the contacts will consume the relays contacts in time.

    Some more points about capacitors though..
    --The Voltage rating of a cap shouldn't affect its life, unless it is too low for the application. 25V caps are still double the rating of the car's voltages. Long term heat/age does kill caps though... As they dry out, capacitance goes down, and leakage current could go up. Eventually, in the case of the GM, the ripple voltages from the alternator, accessories, and the microprocessor switching I/O likely cause it to jump to an incorrect vector and then a watchdog reboot. (About every second)
    --Additionally, The GM caps are likely HOT-AT-ALL-TIMES whereas other caps like those in the IC, DME, IHKA, etc may only be powered when the car is on), decreasing the aging of those parts some.
    Here is a GREAT page/table I just found with the failure modes of capacitors. There are also some nice stories of industrial espionage in the late 90s/early 00s re: elco caps in computer motherboards
    --I suspect there are other bad caps on the car, but none have the same crippling affect as the GM caps (Bad GM Caps --> GM doesn't shut down car --> Standy current kills battery in 4 days --> E31 driver starts buying new batteries --> problem gets "better" for a month --> dead batteries again --> Unhappy E31 driver). There are certainly other problems/gremlins with Instrument clusters, seat modules, door modules, climate control modules, and steering wheel modules that may be attributed to capacitors.
    --However, many capacitors in the car are probably in excess, and failure modes may not even be noticeable.. A logic gate on the RM may only need 0.1uF, so reusing a 1uF part might have been easier.. It would take quite a long time for it to deteriorate to a point where it creates a switching problem.

    Long story short... Pulling and replacing the modules are 80% of the job.. (For those of us that are electrically inclined). There are 5 caps in the RM, it isn't much more work to replace them; However I do agree the 470uF cap is the most important one, which is why I use a Vishay cap with low ESR and 10000hrs@105C (Even though it is 10 times the cost of the others).
    Last edited by EEDegreeToDrive; 01-25-2013 at 09:41 AM. Reason: spelling

    '89 735i, '91 850i, '81 MB 380SLC (For Sale), Tesla Model 3, and VW Passat TDI -- Yes, I still repair General Modules, DM for info!

  15. #40
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    Quote Originally Posted by EEDegreeToDrive View Post
    --The Voltage rating of a cap shouldn't affect its life, unless it is too low for the application. 25V caps are still double the rating of the car's voltages.
    You are correct about the voltage rating having no effect on the electrolytic capacitor's lifespan, but a vehicle's electrical system is a very hostile environment with spikes well above the nominal voltage. With an oscilloscope you can catch transient voltages of 40 V and higher. To be honest I have no clue what the effect of these extremely short spikes is on an electrolytic capacitor, but in my opinion any electrolytic capacitor that is not behind a voltage regulator IC better has a fair margin. Anyway, that's just theory. It's very well possible the voltage is not an issue and the GM just fails due to age and heat. Not that the cause matters very much. The original capacitors lasted 15-20 years. New and better ones will last at least another 20 years. That's not that bad .

  16. #41
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    Thanks for the write up, certainly found it useful in repairing my GM just in case. I am however still experiencing battery drain. 2 days max and my batteries are stone dead. The batteries are brand new BOSCH 90amp units. They replaced a first set of similar units which I assumed were old as I had just bought the car. Is there anything else that can cause such battery drain, I have checked lights, no relays clicking after locking the car, no aftermarket radios or alarm system. Whats my next step?

    Thanks

  17. #42
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    You have to track down the high current... (You'll need one or two beers)
    Disconnect the - battery lug terminal from the trunk on the driver's side to disconnect the both batteries.
    Disconnect/Disable the trunk light switch
    Hook up a current meter in series with the batteries watch the current.
    (You'll have to open the door and toggle your 4-ways to disable the crash relay, which causes ~5 amp pulses as the lights flash).

    Finish your first beer while you wait 16 minutes...

    After 16 minutes (with all the doors shut) the current should drop from about 500mA to 50mA.
    If not, You can double check your GM repair by pulling the two unloader relays. Then, start pulling fuses until the current drops.
    When you find the fuse, open the ETM for your year, and track down the circuit... Good luck.

    '89 735i, '91 850i, '81 MB 380SLC (For Sale), Tesla Model 3, and VW Passat TDI -- Yes, I still repair General Modules, DM for info!

  18. #43
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    You sure two beers going to be enough????

    Thanks for the input, let me try it and see what happens.

  19. #44
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    Hi fellow 8'ies. Having read through all your posts, I have a feeling my GM needs the capacitor repair too, but I would like your comments before I start. What I experience is:
    When the batteries are connected, all exterior lights flash like e alarm has gone off and only stop when I disconnect the batteries. Pressing the alarm enable/disable button the the remote does nothing. Also trying to disable using the key does nothing.
    DOES NOT WORK: Power windows, wipers, window washer, interior lights, passenger door cant open, boot light and boot lock.
    WORKS: Power seats, rear curtain, power mirrors, radio, headlights and the rest.

    Do you think its the GM acting up here?

  20. #45
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    Try pressing the hazard light switch on/off/on/off. That should turn off the exterior light flashing. Then try everything else to see what works/doesnt work. Making the assumption that the batteries are fully charged.
    91 850 (Panzer), 2012 Mini Cooper Countryman (WifeMobile) www.wuffer.ca


  21. #46
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    Hi

    I am about to solve the issue with my car. It has usually been on a garage where temperature is always over 15º. I now changed the car to another garage and temperature is below 12º and is repeteadly failing.

    The locks are dead, no interior light, no windows activity, no wiper activity and after some seconds, click clack in the rear and interior lights go on/ off and sound of locking/unlocking in the boot lock.

    After start up and some seconds (or minutes if cold) it works fine. Once with temperatures under 0º it locked completely and the alarm blocked the car...

    So, my questions?

    1. If I take the module out and change the capacitors and put it back, it works straight away in 100% of cases.
    2. Is there a maximum time where I need to put it back?
    3. Do I really need to disconnect battery? (I do not fancy having reset of all systems)
    4. I could not find the same capacitor voltage, the guy selling them said a higher voltage was not a problem at all.

    470 - 40 not available, I got 470 - 65v
    100 - 25 not available I got 10 - 40v
    10 63 not available I got 10 250v

    la foto.JPG

  22. #47
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    Quote Originally Posted by gon850 View Post
    1. If I take the module out and change the capacitors and put it back, it works straight away in 100% of cases.
    If you don't break it in the process of course... No one can guarantee a 100% success rate - other points of failure could be the A5 relay module (RM), but the symptoms you describe are almost always caused by the electrolytic capacitors in the A1 general module (GM) and fixed by replacing them.

    2. Is there a maximum time where I need to put it back?
    No. In fact you can even drive your car without the module installed but be aware that you do not have wipers without the GM! Definitely not recommended in rainy places.

    3. Do I really need to disconnect battery? (I do not fancy having reset of all systems)
    It is recommended. It's not like there are a ton of settings lost when the car loses power. You'll have to re-enter the date and time, reinitialize the power windows and reinitialize the sunroof. If you have memory mirrors, seats and/or steering column, your custom presets will be lost as well. Also, the engine may run a bit rough for the first couple of kilometers until both banks are synchronized again.

    4. I could not find the same capacitor voltage, the guy selling them said a higher voltage was not a problem at all.
    A higher voltage should not be a problem - the capacitors are just larger. You may not be able to group them as nicely on the PCB as the original ones, but there's plenty of space inside the module.

  23. #48
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    Thanks a lot, I appreciate your help. In fact I was very worried of having the car stuck... I thought it would not run at all. I will let you know how it goes¡
    Last edited by shogun; 08-18-2021 at 09:09 AM.

  24. #49
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    SUBSCRIBED!

    Thank you very much!

  25. #50
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    Hi
    Yesterday I said.... enough is enough.... In Madrid we have a fair weather and the car sleeps in a warm garage but now I do not drive it daily and the batteries are draining... whenever it is cold central lock, wipers, etc... are locked....

    Everything went fine and all works fine (24 hours gone¡).

    One advise.... after you disconnect the module do not leave your keys in the boot... it locks and you will not be able to open it... thanks god I had another key home and could open the boot using emergency method¡

    Thanks revtor and all the previous posts... many 8s have been dismantled for this failure, I am sure¡

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