Can I disconnect the ON-BOARD-COMPUTER

[BINGO]

Howdy,

I recently purchased a 86 635CSI. The previous owner mentioned that the car has a power drain that will drain the battery in 4 days. I noticed from a receipt that a garage traced the fault to the on-board-computer. A replacement runs around $700. I downloaded the wiring diagram and it indicates a "bunch" of fuses and inputs to the on-board-computer. Can I disconnect the computer ? I would guess not base on all of the inputs unless this computer is passive and doesn't actually manage the operating systems.

Any advise would be appreciated !

[John in VA]

Do you mean on-board computer (OBC) that displays time, date, range, etc., or ECU (the "brain" in the glove box)? You can disconnect the ECU, but your car won't run! For the E28 5er, there a a couple of bolts and the front and back that hold the ECU above the inside of the glove box, easier to access if you remove the glove box hing pins to allow the box to drop. Get the numbers off the stickers and you can then pick up a used one for $30-70 from a 635, 535 or 735.

Did you download the appropriate Electrical Troubleshooting Manual here?
http://www.wedophones.com/BMWManualsLead.htm

E24 Forums for help, parts, DIYs:
http://forums.bimmerforums.com/forum...play.php?f=237
http://forums.roadfly.com/forums/bmw/bmw-6-series-e24/
http://bigcoupe.com/phpBB2/index.php...175bdc8fa53bbc

Anita Patton in Winchester had a new OBC for late models:
http://forums.roadfly.com/forums/bmw...9422272-1.html

We also have quite a few E24 owners on the E28 forum - many shared systems and components:
http://www.mye28.com/

[BINGO]

I mean the on-board-computer. For the time being I would like to disconnect it to confirm the previous diagnosis and to use the car while I track down what part of the OBC assembley is at fault. Thanks for all of the links. I am sorting through them. Most deal with replacing the bulb and how to program it.
Yep that's the electical trouble shooting manual I downloaded. It shows the that the OBC is connected to a number of fuses and recieves a number of inputs. I can't tell if the car will run if I disconnect the thing. I hope that I can gain access to a single connector without taking the OBC out. Later models required removing the radio.Well since I need the serial number for the radio I guess I can kill two birds with one stone. Interesting that the ECU is $30-70 and the OBC runs $700.

[John in VA]

I'm not familiar with the E24 OBC to know if it differs from the others used in the same period. The E30 3er is the same as the E28 5er one, except for the coding key, and that is transferable. The OBC unit itself also sells for $30-50 used.

[BINGO]

John,

I bought the ODBC input/info modular off of EBay for $50. They run about $650 new. I'll install it as soon as the weather warms up.

[John in VA]

Hopefully you have some idea how to approach the task. Accessing the OBC on the E28 only requires removing the 2 vertical screws that hold in the instrument housing, while the E30 unit is a bear!
Make certain the light bar (white plastic rectangular unit with the bulbs that illuminates the display) is good before you put everything back together!