Success in General Module Repair

[FastMover]

Thanks for the lead in... Good info, ah pics and all.

I was replacing the map light bulbs with the door opened, so interior lights were on while I was doing this. I think I shorted the circuit, as I was using a screw driver to bend the mounting contacts to better hold the bulb. All of sudden, at that moment all the interior lights when off. So is this a capacitor issue or is there a fuse on the GM board? No GM issues at all prior to this happing last week... Checked all fuse front and back, all good. Darn should have know better.

Thanks..

[revtor]

FastMover: Double-check fuse F33 in the rear power distribution box.

[Sniff38]

I wanted to get input from the E31 electricians out there to see if my GM might be the culprit.

I have a '92 850 with only 36K miles, but from what I understand the capacitors degrade over time, not mileage. My car is not a daily driver and the batteries seem to drain after a week of non-use. I've made sure the factory mobile phone was properly disconnected as I've read that can be the cause of battery drain. All checks good. I've since put the car on a CTEK battery maintainer.

In addition to the battery drain, my passenger side window is acting a bit finicky when I try to raise it using either the driver or passenger side window switch. The driver's side switch was replaced by the dealer a few years back. When I raise the window, it stops half-way up then jumps up and down. I release the switch to make it stop. In order to get the window to retract without issue, I have to press on the switch very hard. I have no issues with the driver's side or either rear quarter windows. Add to that when I select reverse (manual transmission), the passenger side mirror tilts down, but then jumps up an down. I've since deselected that function using the mirror selector switch.

Could my GM be the cause? If not, what do you think it is? Is it worth rebuilding the GM anyway as my car is 24+ years old? All my lights work fine and my electrical issues seem to be minor compared to others I've read on here.

As always, much appreciated.

Sean

[Timm]

That sounds more like the problems I had when my window/mirror switch failed as described here:

http://www.meeknet.co.uk/e31/BMW_E31...r_Switches.htm

To check if you have battery drain (rather than dead batteries), measure the current between the common ground point for the batteries and chassis using a meter - otherwise it is just a guess if there is battery drain:

http://www.meeknet.co.uk/E64/TIS_Rou...easurement.pdf

[Sniff38]

Thanks Timm. Congealed contact grease would certainly be a logical explanation for the finicky tilt function on the passenger side mirror. However given my problem only occurs when I put the car in reverse, would the problem be with the mirror selector switch in the door or something connected to the transmission (I have a manual)? As far as the window is concerned, the previous owner replaced the driver's side door switch 8,000 miles ago (back in 2009) at a cost of $350 (ouch). I can't imagine that switch is bad again or the grease is congealed. Nevertheless I'll remove the unit and take a look.

I appreciate the battery drain document in your second link, but to be perfectly honest I felt like a dog looking at a newspaper at times. I only had one Electrical Engineering course in college and I can't say I remember very much of it. Where exactly is the "common ground point" for the batteries you are referring to?

Any value in a pre-emptive rebuild of the GM?

Sean

[Timm]

I'm sorry for my glib explanation of closed-current testing - I was in a bit of a rush! There is an easier way to test for current drain and that is to:

Ensure both batteries have a good charge in them
Take the key out of the ignition and put it in your pocket
Shut both doors - windows and sunroof closed
Disconnect the negative terminal of both batteries as shown here:

http://www.meeknet.co.uk/e31/E31_Bat...eplacement.htm

Get yourself a current meter with big crocodile clamps at the end - the meter must be able to measure 20A of DC current

Connect the black lead of the meter to the left hand cable that you took off the negative terminal of the left battery
Connect the red lead of the meter to the left-hand battery negative terminal (you can ignore the right-hand battery for these tests as long as the negative lead on it is disconnected)

Your meter will now show the current being taken by the car - as long as the meter leads are long enough put the meter out of the boot and close the boot on the leads - they will not be damaged

The meter should show that the current drain is a couple of Amps for a minute or so and then the current will decrease until 16 minutes later when it should reduce to 0.05A (50 milliamps)

During the 16 minute period don't open any doors or fiddle with the key

Although the artical below is for the E38 it does discuss battery behavior and problems associated with infrequent usage of the car. A battery can be irreparably damaged in a month at 0% state-of-charge

http://www.meeknet.co.uk/E38/E38_Battery_Drain.htm

[Sniff38]

Thanks for the clarification Timm. I will try your procedures next time I'm in the garage.

- - - Updated - - -

Still hoping someone will weigh in on the value of pre-emptively rebuilding your GM with new capacitors.

Sean

[clockwork]

Preventative maintenance on a GM is never a bad thing. I am due but keep forgetting about it. I will pull soon and send to a pro. On this forum.

[UNEEKONE]

I plan on pulling mine out this weekend. Its supposed to be 50 degrees so it should make for a pleasant mid-winter project in the garage...

[EEDegreeToDrive]

Hi Folks--
I just wanted to chime in and thank you all for trusting me with your modules. At least a dozen of you (Stateside) have sent me your GMs for repair this past year, despite me participating only a little bit in the forums. I can only gather folks are good with the search feature, or I'm being recommended by others in the forum, to which I am thankful. For reference, I charge $45 for replacing the capacitors, including return shipping via USPS Priority mail; With the cost of the capacitors (About $4-5 in bulk) and return shipping ($6), I'm certainly not making a killing on the deal, but do try to drop everything when I receive a module so I can get it turned around ASAP; and I'm happy to continue doing it to preserve the GM module population and prevent modules from being damaged by inexperienced folks. I'm certainly not the authority on the modules, many thanks to those that came before, incl Revtor, Spandrel, and, of course, Shogun.
It's been a busy few years with work (I'm a Software Engineer), acting in community theater(2-3 different productions/year), running an AirBNB property remotely, among other more personal things(nothing terrible). My poor E31 has been sitting in my 2nd garage in upstate NY for at least a year, awaiting a weekend that I can change the heater core! I did get rid of a car or two (E34, E46), and when things wind down a bit, I'll have more time for my E31; Thanks again!

- - - Updated - - -

Thanks for the clarification Timm. I will try your procedures next time I'm in the garage.

- - - Updated - - -

Still hoping someone will weigh in on the value of pre-emptively rebuilding your GM with new capacitors.

Sean

If it's original, then you should probably have it serviced; The capacitors are like batteries, they dry up over time and stop functioning as well as they do initially, eventually leading to a rebooting general module, particularly since the GM (and a few other modules) are powered non-stop from the day the car was born.

- - - Updated - - -

As far as the window is concerned, the previous owner replaced the driver's side door switch 8,000 miles ago (back in 2009) at a cost of $350 (ouch). I can't imagine that switch is bad again or the grease is congealed. Nevertheless I'll remove the unit and take a look.

Sean-- If you suspect the window switch, try the windows with your key-- (Many folks forget BMWs do this!) Hold key to clockwise/lock position for ~10 sec and it'll roll the windows all the way up; Similarly, hold it to unlock for 10s and it'll roll the windows down and then open the sunroof.

Also don't forget, the window switches have 2 positions, the 2nd indent is for automatic opening/closing, which has to be synchronized after connecting the battery by rolling the window full up and down at least once. Both light press and hard press should cause the windows to move.

If it's just the passenger side, remember there are door cards in both doors. It's also possible (but less likely) there is an issue with the relay module, which actually does the 'heavy lifting' for the GM. The GM is the brain, the RM is the brawn.

Another possibility is that BMWs have load monitoring on certain devices like windows/sunroof to protect someones hands getting stuck, particularly important with automatic operations. If you overload it, say with a hand in the way, or perhaps a jammed track, the RM/GM will cut the windows off for a period of time.

I'll keep an eye out for your GM in the mail, but it's certainly possible the window issue may extend beyond the scope of typical GM issues.

--Scott

[dragon850]

Thank you for providing this service at an excellent price!!

[UNEEKONE]

Thank you for providing this service at an excellent price!!

Ditto. Just dropped mine in the mail earlier today!

[EEDegreeToDrive]

Well everyone--
Thanks to ~3 recent GM repairs, You've caused me to blast through another $60 in conformal coating and electrical contact cleaner.. :-)
Of course, that's another reason to send modules my way, I've got all the right tools and supplies :-)

For reference, here's what I use:
To clean off solder flux after removing old capacitors, after cleaning holes, and after soldering new capacitors in:
CHEMTRONICS ES896B Flux Remover, Flux-Off, Brush Applicator, 6fl.oz

To coat the fresh solder and capacitors so they're not exposed to moisture/condensation:
TECHSPRAY 2108-12S Coating, Conformal, Transparent, Aerosol, 12fl.oz (US)

For cleaning the edge connectors and sometimes for cleaning before coating, and generally a good idea for any other connectors, this plastic-safe cleaner
CRC QD Electronic Cleaner

Thank you for providing this service at an excellent price!!

No problem; You're welcome.

Ditto. Just dropped mine in the mail earlier today!

Received, repaired, and ready to ship out tomorrow...

Also folks, it seems that USPS just raised the price on Priority Mail again.. It seems the Priority Mail Flat-Rate padded envelopes are slightly better priced now, not sure if they offer the best protection though.

- - - Updated - - -

...and for reference again, the capacitors I use:
Vishay 470uF 40V 138AML 105C (Low ESR, Only 0.34 Ohm) Newark #14M6702 (Perfect fit)
Vishay 100uF 25V 516D 85C Newark #83K6263 (About 1-2mm longer than ideal, but fits OK)
Vishay 47uF 25V 516D 85C Newark #83K6372
Vishay 1uF 50V 516D 85C Newark #83K6237
Vishay 10uF 50V 516D 85C Newark #83K6249

Note: The main capacitor I buy is rated to 5000 hours at 105C, which should be good for a few dozen years unless you leave your car in death valley for a year or so.

[Sfdon]

What a great resource!
thank you!

as an aside- my friends graduation test at tech school in Deutschland was to replace an 850i heater core.
thats a $6000.00 job
40 hours of labor?

[dragon850]

Maybe BMW book... Usually takes 2 days, 8 hours each so 16h... at least for me. Done it twice and will not do it again.

[Sniff38]

From EEDegreeToDrive: "Also folks, it seems that USPS just raised the price on Priority Mail again.. It seems the Priority Mail Flat-Rate padded envelopes are slightly better priced now, not sure if they offer the best protection though."


I just mailed mine in the VHS cassette-sized flat-rate Priority Mail box. It's the perfect size for a GM plus a little padding. The flat rate price only increased 37 cents, so it definitely isn't worth risking damage by shipping it in a padded envelope. To replace a GM from the dealer will set you back over $500.

Sean

[Bimmer8604]

Another happy customer from EEDegreeToDrive. I mailed him mine on a Wednesday and had it back the next Monday. Couldn't be happier!

Kyle

[UNEEKONE]

What a great resource!
thank you!

as an aside- my friends graduation test at tech school in Deutschland was to replace an 850i heater core.
thats a $6000.00 job
40 hours of labor?

I have receipts from the PO from 2009 or 2010 and it was around $5000...

[EEDegreeToDrive]

What a great resource! thank you!

as an aside- my friends graduation test at tech school in Deutschland was to replace an 850i heater core. thats a $6000.00 job
40 hours of labor?

Maybe BMW book... Usually takes 2 days, 8 hours each so 16h... atleast for me. Done it twice and will not do it again.

Yeah-- My E31 has a heater core leak-- Probably just the O-Rings; Fortunately I have a 91, so don't have the pass airbag to worry about. One of these weekends I'll get to it. I'm terrified of getting in there to it only to find out that every plastic HVAC flap in the system is broken/will break just looking at it.
My E32 has had a tiny coolant smell/leak for the last 10 years... It's got 250K miles on it now.

I just mailed mine in the VHS cassette-sized flat-rate Priority Mail box. It's the perfect size for a GM plus a little padding. The flat rate price only increased 37 cents, so it definitely isn't worth risking damage by shipping it in a padded envelope. To replace a GM from the dealer will set you back over $500.
Sean

It can be packed safely with either method. I usually send them back in the same box received. Interestingly though, one of the last ones received in the VHS size flat-rate box had the box crushed somehow! Regardless, the module doesn't have any moving parts and is not /that/ delicate. It's also a pretty thick board with a lot of copper, so not likely to crack, even if stepped on. I typically suggest the flat-rate boxes since it's quite easy to double the shipping cost putting it in a different sized box.

Another happy customer from EEDegreeToDrive. I mailed him mine on a Wednesday and had it back the next Monday. Couldn't be happier! Kyle

Again you're welcome.
/end_thread_jack

[UNEEKONE]

So I just installed my GM that was remanufactured by Scott. Thanks for the fast turn-around! Everything appeared to be working properly- i.e. the windows, wipers, etc. but then I looked at the gauges and they were completely dead. Nothing. Anyone else have this problem? I removed the plugs from the module under the GM to be able to get it removed easier. The connectors all went in nice and smoothly. Is the lower module the one that controls the gauges??? Any thoughts are appreciated!


Sent from my iPhone using Tapatalk

[Sniff38]

I just had my GM repaired by Scott and it's still in the mail. I'll let you know what I experience as I had to disconnect the lower module as well in order to get to the GM. Hopefully your situation is something simple.

Sean

[UNEEKONE]

I just had my GM repaired by Scott and it's still in the mail. I'll let you know what I experience as I had to disconnect the lower module as well in order to get to the GM. Hopefully your situation is something simple.

Sean

Please do. You'll be pleased with the results. He has skills...

[revtor]

Everything appeared to be working properly- i.e. the windows, wipers, etc. but then I looked at the gauges and they were completely dead. Nothing. Anyone else have this problem? I removed the plugs from the module under the GM to be able to get it removed easier. The connectors all went in nice and smoothly. Is the lower module the one that controls the gauges???

The gauges are indeed controlled by the lower module - the A25 body electronics module (EKM). Maybe you did not insert the connectors properly upon reassembly? It's important to open the latch fully before inserting the connectors. Otherwise the connectors don't go deep enough and may not make good contact. A fellow forum member had this same problem recently (link). Reseating the connectors fixed the problem.

[UNEEKONE]

The gauges are indeed controlled by the lower module - the A25 body electronics module (EKM). Maybe you did not insert the connectors properly upon reassembly? It's important to open the latch fully before inserting the connectors. Otherwise the connectors don't go deep enough and may not make good contact. A fellow forum member had this same problem recently (link). Reseating the connectors fixed the problem.

Awesome. Thank you for the link!

[Sniff38]

Well I just installed my rebuilt GM and everything is working like a champ (thank you Scott!). I'm not sure it made any difference, but I disconnected the batteries before I removed the GM and didn't reconnect them until after I had the unit reinstalled. I'm also happy to report rebuilding the GM solved my finicky passenger side window (see post #78).

If you are like me and don't want to risk buggering up your GM circuit board, then I highly recommend the rebuilding services offered by EEDegreeToDrive. I figured I'd leave it to the expert . . . probably the best $45 I've spent on my 8 series so far. Also if you are bothered by electrical gremlins and can't figure out what's causing them, then perhaps a GM rebuild might be your solution. I was originally approaching this as a pre-emptive rebuild, but it actually fixed an issue with my car that was rather annoying.

Sean