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The On-Board Computer (OBC).

Last updated 1/2/97

Undocumented Features.

These work on OBC II cars:

Simultaneously press the 1000 and the 1 button to get remaining fuel in liters (the car needs to be running).

Simultaneously press the 1000 and the 10 button to get the version number. You should get something like:

4 .6TYP

Where the 4 is the car/engine designator, the 6 is the chip firmware. That tells you the programming of the OBC, what coding plug is in it. Specific to each engine type, injector type, tire size, fuel tank and reserve capacity. And here's some more from Phil Marx....
OBC car/engine designators and firmware number.
E30 318i 3-3 TYP
E30 325e ('84-87) 3-8 TYP
E30 325e ('88) 4-4 TYP
E30 325i ('87) 3-1.2 TYP
E30 325i ('88 on) 4-6 TYP
E30 M3 3-1.1 TYP
E28 528e ('85-87) 5-8 TYP
E28 528e ('88) 5-1.3 TYP
E28 535i 5-6 TYP
E28 M5 6-4 TYP
E24 635Csi/L6 ('85-87) 6-2 TYP
E24 635Csi ('88 on) 6-6 TYP
E24 M6 6-4 TYP
E23 735i/L7 ('85-87) 7-4 TYP
For what this bit of knowledge is worth to anyone....... No other test functions on that type OBC but you'd need a book to discuss the E32/4 type.
- -Phil Marx BMWCCA #6021

The following is for newer OBC found in E36 cars for example:

To determine if your OBC is eligible .. press 1000 and 10 together.
you should see TEST NO . -- or something like that.
Now, some of the functions are locked out -- I do NOT recommend messing with them and you do so at your own risk -- that said ...

To unlock all functions .. press 1000 and 10 and at the TEST prompt enter 19 using the keys .. press SET/RES .. you should see LOCK:ON or something similar ... press the DATE key .. (today you'd see 08.20) and add the two numbers (day and month) together (today 28)

Now enter the number you just calculated (28) and press SET/RES. TADA .. you have unlocked the secret functions ...

To lock them back up .. press 1000 and 10 then enter 19, SET/RES now press SET/RES again .. it should show .. LOCK:ON again

In general when I show a test enter it by pressing 1000 and 10 together then enter the number of the test with the numeric keys and press SET/RES to actually execute the test ...

Test numbers for E36 OBC (Note: Joe this should also work for your 535!)
Test no.
1 Display Test .. all LCDs and LEDs activate
2 Current Consumption in l/100km
3 Current Consumption in l/hour
4 Average Consumption (used to calc. Range)
5 Current Range
6 Not used ..
7 Average Fuel in Tank (l)
8 Current Speed (km/h)
9 System Voltage at terminal R
10 Country/Language
11 Units/ AM.PM
12 Average Speed (km/h) for calc. ETA
13 ETA
14 Date of software/mask of OBC
15 Production Diagnosis (??)
16 Production Diagnosis (??)
17 Display Vehicle Specific Data
18 Alarm Changeover (continuous v. intermittent)
19 LOCK/UNLOCK all functions
20 Correction Factor for OBC Fuel Consumption (SEE BELOW!)
21 Reset all defect codes, date and time ... activate by pressing SET/RES
Note on test #20:
The factor is used to correct the OBC Avg Fuel Consumption figure to reality. If your OBC is off a bit: fill UP totally, run tank down and refill; then calculate your Actual MPG. Now enter test 20 to get the old Correction Factor.
Enter the NEW CF using the numeric keys and hit SET/RES to store. PLEASE record your OLD CF so that IF you screw up you can always go back to what it was.

This is from a European 1990 M5 owner (9/3/96):

I have also found a deviation from the FAQ (which describes an E36 OBC) in the 'lock/unlock secret functions' of the E34 OBC:
To unlock:

To lock:
The procedure to show the version number also differs from the FAQ. On the E34 OBC, you need to press the 100 and 1 buttons simultaneously, to display the type/version (Mine shows '5-00TYP').
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Fixing the backlight:

This is about a 1988 325is(aka E30), but many other models are similar.

A variation of this note appeared in the Feb., 1994 Roundel and is included in the "BMW Enthusiasts Companion" book published by Bentley.

The backlight for the OBC display is provided by a pair of small incandescent bulbs which are soldered to a small printed circuit board. This board is in a white plastic housing that slides into the right side of the OBC. The bulb assembly cost about $20.00 from the dealer. A resourceful hack mechanic could save 20 bucks by unsoldering the old bulb and soldering in a new one. You probably would have a hard time finding an exact replacement bulb but you could find one close enough.

Added. 11/2/94...

The bulbs are 5 Volt and use about 80 mA. The nearest Radio Shack bulbs are: part number 272-1140, 6 volt. They can be soldered right in the circuit board.

The hard part is getting at the side of the OBC to remove the bulb holder without disassembling the entire center console. You must partially remove the center console panel. The OBC is screwed into the center console panel from the rear with 4 phillips screws. Once the screws are out, it comes out toward the rear (unfortunately!!).

First I removed the radio by loosening the screws that lock it into the center console. These screws are a special 5 sided torx-like screw that require a special tool to remove properly. The tool costs something like $15.00 at the dealer, but you can usually get by with a 2mm hex wrench. It's really maddening that of all the worhtless crap in the BMW toolbox that comes with the car, they cant put this $0.50 tool in. The hex wrench might chew up the screw a little bit, but it will still work repeatedly. I did all this with the battery connected so I didn't have to reset codes or reprogram the computer. No electrical connectors have to be removed so there's not much danger of shorting things. The radio has long enough wires that you can pull it out the front and rest it on the ashtray while you do the rest. The E30 Bentley manual really helped on the next step because it showed the location of the screws that hold the center panel. There are 2 #1 Phillips screws at the top, behind the hazard flasher switch, which you have to pull out and leave dangling by the wires, the other behind the dummy plug. The 2 #2 Phillips screws at the bottom are harder to reach--you need a short screwdriver--but they're not that tough. Once the four screws are out you can pull the center console out enough to access the computer. You have to be careful not to snap off plastic edges, slide the panel to the right as you pull to free the lip on the left side. Note that everything (heater controls, radio balance control, etc.) is still connected to the center console. This makes it a little harder to maneuver, but it's a lot less work in the end. [See below for alternate method to removing bottom console screws.] If your wrist is small enough, you can reach in through the radio opening and loosen the 2 Phillips screws that hold the left side of the OBC. You don't need to remove the screws, just loosen them. If you can't fit through the radio opening, you'll have to remove the glove box and side panels to reach the screws from behind. Now with the left side loose you just need to pull the right side of the center panel out about 2 inches until you can access the left side screws. At this point you can see the flush mounted bulb-holder and you realize that this thing was not very well engineered! The center panel cutout blocks access to the slide out bulb-holder. That is why you have to remove the 2 screws holding the left side of the computer. It would have been an easy matter to design a center console that didn't block the bulb. For that matter, it seems it would have been easy to design a computer mount that allowed it to just snap out toward the front or screw out like the radio. The bulb could then be changed in 30 seconds. Back to the 2 left side screws--to really get a screwdriver on these you would have to pull the center panel out at least 4 or 5 inches. It didn't seem like it wanted to be pulled out that far without removing more stuff (like heater controls) so instead I just opened it enough to get a pair of small needle nose vise-grips on the heads of the screws. They aren't in very tight so with a little patience the vise-grips remove the screws.

[Addition from Rick Kjeldsen: The center panel will come completely off the heater if you do the following: Take (pull) off the caps from the 3 heater slider controls. There is a thin plastic cover over the three slider slots that covers 4 screws. It is about the size of a 3x5 card. You have to gently pry it off to avoid damaging it. I found I can pull from one of the slider slots to get it started. That will uncover 4 screws that hold the center panel to the heater core.]

Now the on-board computer can be pushed in from the center panel, the bulb-holder pulled out and the new one slips right in. I checked the old bulbs and sure enough one was burned out (they're in series so this takes out the other one). Just to make sure before I closed everything up, I stuck in the key, turned on the ignition and the correct time of day lit up beautifully!

I just reversed the procedure to get everything back. The biggest problem here was restarting the 2 bottom screws on the center panel. It's impossible to see anything and there isn't enough room even for my small hands. A little patience will get you there though.

[11/5/93 Update: You might be able to get away with this easier method, supplied by Kent Shephard which worked on his M3]

My mechanic showed me how to do this on my M3 today and he said this description is *NOT* the way a flat rate mechanic does it. He works for a dealership and he did my M3 is all of 10 minutes. So folks I'll outline it so the FAQ can be changed. He said all the screws don't need to come out. He said this description is for those obsessed with getting the computer out. So follow along.


At this point tilt the top of the console forwad. Don't be scared you won't break it. You will now be able to look on the right side of the computer and see the light module and a single screw. You will need the needle nose pliers to remove that screw. It has fine threads so be patient. Throw screw away. The computer will hold fine with three screws. After the screw is out, pull the module with the needle nose pliers and it will come out. Now slide the new one in and reassemble.

Here is another person's experience. Note this is in conflict with the above--namely in that the OBC comes out toward the front and is held in by nuts not phillips screws. Maybe BMW used different methods. I think sometime in the early 90's the OBC does snap out toward the front simply by prying with a credit card. (can somebody verify this and e-mail me.

(by Mike Whitley:
A lot of people have complained about the backlight on the E30 onboard computer. When I had a 325is, the lights burned out. Replacing the little panel or even just the bulbs is an easy job. Saves you $70 or $80 as well compared to letting a dealer do it. A quick summary follows.

Access the computer... this involves first taking out the glove box, and right side dash board cover. Everything is held in place by push pins, they just twist and pull out.

Now, you need a socket wrench, with a short handle and a very small socket. I can't remember how big... anyway, use the wrench to undo the nuts that hold the computer in place on the dash baord. You won't be able to see them just feel around and you will find them. Once the nuts have been removed, the computer will slide out of the dash towards the seats.

On the side of the computer is a small white panel. This is the back light bar. Pry it out with a small screwdriver or fingernail and pop in the new one. If spending $25 or $30 for this seems like a waste of money to you, desolder the dead bulbs and solder in new ones for about $2.00. They may not have the exact same wattage though. If the computer push buttons have also stopped lighting up, the bulb for that is located in the back. Twist it out and pop in a new one. (You remembered to pick one up at your dealer right?)

Reverse the installation instructions and voila! You are done. The whole thing shouldn't take more than two hours. Less if you are quick.

(by Steve Fox:
Alternate method:
Remove radio (easy).
Pop top switches above radio (easy).
Remove two phillips screws at top of center console. They will be visible through the recently vacated switch holes (easy).

Remove two phillips screws at bottom of center console, just under bottom edge (easy).

Pull center console forward on the right edge exposing the business side of OBC (easy, but gently, not much distance needed).

Remove top right nut that secures OBC (easy).

Trim pointless plastic interfering with removal of light bar (easy, makes next replacement even easier).

Pull out light bar with needle nose and replace with new unit (easy).

Assemble in reverse order of disassembly (easy).

I did this in 20 minutes the first time. The other method on this list (through the glove box) sounds great too but I could not contort my fingers enough to remove the four OBC nuts. Local dealer wants about $80 for this procedure.

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What to do if you get PPPP displayed on the OBC

I've heard that disconnecting the battery for a long time (like 1 hour) will make this go away.

I lived with this problem for several (3) years. I tried disconnecting the battery for the 1+ hours or so to no avail. The ultimate solution was to disconnect the computer itself from its multi-pin connector. I left it unhooked for approximately 24 hours. Upon reconnecting the computer.....viola a full up and running OBC II.

Jeff Wilcox
So here is what works most of the time.

With the key in the "Radio" position (Radio and OBC light up, but not the instrument cluster), press the "CODE" button. Then push the little reset-hole with a Pen and hold it, 'till the computer blinks in the display, and it will ask you for a time and date entry. - You now have re-adapted the coding plug to the computer. - Normally the computer goes into a PPPP mode when the car has been boosted, or some other very drastically voltage changes have occurred.

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