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.

I will preface this write up by saying that Matt Rhoads has an excellent write up on how to do this procedure and it includes all the part numbers. I am just going to regurgitate most of the information he said and add my installation pictures.

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 -Non Airbag Equipped Cars	61 31 1 375 190 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
	9/1987 on		65 81 1 385 939
	w/ extra fuel tank		65 81 1 376 033or 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
	10/1986 on		65 81 1 381 795
	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 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.
	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.
	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.
	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.
	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.
	Here is the new coding plug.
	Install the new coding plug (if necessary) into the OBC.
	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.
	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: 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?