M42club.com - Home of the BMW E30/E36 318i/iS
FAQ / REFERENCE => How-To's => Topic started by: DesktopDave on December 24, 2010, 07:56:42 AM
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318i Modification -
OBC Retrofit
The miniature on board computer that came with my 318i is pathetic. It only lists date/time and temperature. The full function OBC has many more functions including range, MPG, a timer, a speed limit chime, a code feature, and more. I've always been jealous of cars with the full OBC. To make matters worse, my mini-OBC has a problem where it will randomly stop working correctly. The characters on the screen start going berserk and it looks like the Predator's self destruct sequence after Arnold drops the tree on him.
Below is a list of all the parts in the OBC system:
BMW Part; BMW Part Number
OBC Control unit; 65 81 1 386 867
OBC Light Bar; 65 81 1 375 461
Upper Wiring Harness; 61 12 1 385 794
Coding Plug; See Table Below
Turn Stalk with OBC Control
-Airbag Equipped Cars; 61 31 1 375 190
-Non Airbag Equipped Cars; 61 31 1 377 966
Relay Box; 65 81 1 373 726
Screw; 07 11 9 916 973 (2x)
Lower Wiring Harness; 61 12 1 386 982
Alarm Horn; 61 33 1 379 090
Horn Wiring Harness; 61 21 1 380 016
Most of the above equipment is available on eBay. That is where I purchased all my OBC equipment. Be careful with eBay because many sellers tend to ignore model year differences and say any stalk will work in any car. This is somewhat true, but not perfect. For example, if you have an airbag equipped car and you purchase the turn stalk from an older E30, the stalk dimensions will be different and the stalk will feel too far away.
Not all the parts are necessary. The relay box, screws, lower wiring harness, alarm horn, and horn wiring harness are all needed if you want to use the code function on the OBC. The code function disables the car until you type a code into the OBC. I have this feature on my E36 M3 and I never use it and decided to skip the hassle necessary to install it.
I also don't believe the turn stalk is absolutely necessary. The OBC enabled turn stalks allow you to press the stalk toward the steering column and it cycles the OBC throughout all the OBC modes. I think it is worth the effort as replacing the stalk is not that difficult.
Before you install your new OBC, make sure you have the correct coding plug in the OBC. The coding plug is located on the back of the OBC and tells the computer important details about your car, gas tank, and engine. Below is a list of the different coding plugs. Most OBC's for sale are from a 325i/is/e/es so your OBC will probably come with the coding plug for that particular engine. Life is more difficult if you have a 318, a 320, or a 323.
Car Model; Years; Engine; BMW Part Number
318; 1982 to 9/1985; M10B18; 65 81 1 375 816
320; 1983 to 9/1987; M20B20; 65 81 1 376 032
320; 9/1987 on; M20B20; 65 81 1 385 939
320; 9/1987 on; M20B20 w/ extra fuel tank; 65 81 1 376 033 or 65 81 1 381 319
323; 1983 to 9/1987; M20B23; 65 81 1 376 032
325i; 9/1987 on; M20B25; 65 81 1 385 941
325e; 1983 to 09/1986; M20B27; 65 81 1 373 698
325e; 10/1986 on; M20B27; 65 81 1 381 795
325e; 10/1986 on; M20B27; w/ extra fuel tank ; 65 81 1 381 320
318i/is; 1989 to 09/1991; M42; 65 81 1 394 111
M3; 9/1987 on; S14; 65 81 1 380 891
Matt makes note that the coding plug for the M10B10 may not be accurate because the coding plug was designed for the M10B10 as used in the E28 518i which had a 70l fuel tank as opposed to the 55l tank in the early E30 318i. There is also no plug for the M40 motor or any diesel motors.
Considering no 1991 US 318i or 318is come with the option of the full OBC, I had to purchase a new coding plug. Bavarian Autosport was able to get it for me but it took a few weeks as it was a special order.
Before we begin, here is a table of the connections of the upper wiring harness:
Connector Color; Number of Pins; Wire Colors; Connects To:
Green; ?; ?; OBC
Yellow; 20; ?; Instrument Cluster
White; 2; Blue and Brown ; Outdoor Temp Sensor
Black; 4; ?; Door Chime
Blue; 1; Black; OBC Turn Stalk
2 x White; 3; ?; Connect together
White; 2 ; Green and Green/Red; No Connect
White; 1; Yellow; No Connect
Let's begin the retrofit! Remember that my 1991 318i may be slightly different than your car.
Click on the thumbnails for larger pictures.
Remove the steering wheel and cluster as described in my Dash and Cluster Light Replacement (http://web.archive.org/web/20070210110005/http:/zoso.no-ip.org/318i-dash.html)write up You will also need to remove the knee bolster.
Two screws hold the turn stalk on. Remove the two screws.
Slide the turn stalk relay off it's mount.
Enjoy the mess under the car.
Trace the turn stalk wires back to the connector. The connector is plugged in and two other connectors are wedged around it. Slide the connectors apart.
(http://i729.photobucket.com/albums/ww299/desktopdave/BMW/Zoso/318i_obc/05-speaker.jpg)
While you are down under the dashboard plugging in the new turn stalk connector, find the door chime. Mine was just handing so I'm not sure where it really belongs. It is pretty unique looking and has two connectors plugged into it.
With the instrument panel removed, find the yellow connector. This is your mini-OBC wiring harness. You can trace it both ways to go to the mini-OBC and the door chime.
Remove the face plate of your mini-OBC and squeeze the prongs to remove your old OBC. Pull the handle up and remove the crappy OBC from your car.
(http://i729.photobucket.com/albums/ww299/desktopdave/BMW/Zoso/318i_obc/08-parts.jpg)
Here is an overall look of how the full OBC harness plugs into each component. The two pin white connector attaches to the outdoor temperature sensor. I found my temperature sensor connector in the same area as the door chime. Trace the old wiring harness back if you can't find it.
(http://i729.photobucket.com/albums/ww299/desktopdave/BMW/Zoso/318i_obc/09-cluster.jpg)
Yellow connector plugs into the back of the instrument cluster. The one pin blue connector attaches to the turn stalk.
Black connector connects to the door chime.
Green connector to OBC. The small white connector attaches to nothing.
Install the harness in the car's dashboard. I left my old mini-obc wiring harness in the car because it would have been too much effort to remove it. Route all the connectors to where they should end up.
Install the new OBC stalk. Make sure to remember to screw in the brown wire with the metal loop.
(http://i729.photobucket.com/albums/ww299/desktopdave/BMW/Zoso/318i_obc/13-relay.jpg)
Slide the turn stalk relay into it's mounting position on the steering column. Connect the OBC wire and reconnect the turn stalk connector to the car.
Here I am removing the old coding plug from the rear of the OBC. Evidently this OBC started it's life in a 1987+ 325i/is.
(http://i729.photobucket.com/albums/ww299/desktopdave/BMW/Zoso/318i_obc/15-m42codingplug.jpg)
Here is the new coding plug.
(http://i729.photobucket.com/albums/ww299/desktopdave/BMW/Zoso/318i_obc/16-m42codingplug.jpg)
Install the new coding plug (if necessary) into the OBC.
(http://i729.photobucket.com/albums/ww299/desktopdave/BMW/Zoso/318i_obc/17-newobc.jpg)
Remove the center console face plate. This is somewhat of a pain. First remove the radio. Slide out the buttons above the radio and any blanks. Remove the tabs on the vent sliders by pulling on them gently. With the tabs removed, use a small screwdriver and gently remove the faceplate that is around the vent sliders. Remove the four phillips head screws that are behind the faceplate. There are 4 more screws holding the center console into the dash. Feel around up top and you will find two. The other two are accessible from below in the storage bin.
With me to this point? Ok, good. Next, unscrew the bracket that used to hold the mini-OBC. Remove it. Use the four brass colored screws to directly mount the new OBC.
(http://i729.photobucket.com/albums/ww299/desktopdave/BMW/Zoso/318i_obc/18-halfassembled.jpg)
Start to reassemble the dash and cluster. If you don't care about airbag warnings (or if you don't have one), put the keys in the ignition and test it out.
Let me give a word of advice at this point. Don't do what I did and forget to order a new light bar. The light bar is what illuminates the OBC display. There is a white tab on the right side of the unit. Use a pair of needle nose pliers and pull it out and slide a new one in. Getting to the OBC is much more of a pain that it was to get to the mini-OBC so do this now because if you don't, the light bar will already be burnt out or will burn out a month later. You know it will!
Performed:
May 21, 2005
Mileage
170,000
Difficulty:
2.5 /5
Disclaimer:[FONT="] I am not a professional mechanic. Information this page should be used at your own risk and discretion. Different models and model years may be different than my 1991 318i. Read: If you screw your car up following my instructions, sorry. Isn't it sad that in this sue crazy world you have to put a disclaimer on your web page? [/FONT]