To determine if your OBC (computer) 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 and you should see LOCK:ON or something similar. Press the DATE key (today you'd see 09.02) and add the two numbers (day and month) together (today 11).
Now enter the number you just calculated and press SET/RES and you have unlocked the secret functions.
To lock the functions back up, press 1000 and 10 then enter 19, SET/RES and then press SET/RES again. It should show LOCK:ON again.
In general, to use a function, press 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:
Test no. Description
1 Display Test - all LCDs and LEDs activated
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
12 Average Speed (km/h) for calc. ETA
14 Date of software/mask of OBC
15 Production Diagnosis (?)
16 Production Diagnosis (?)
17 Display Vehicle Specific Data
18 Alarm Changeover (continuous/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 the tank up, run tank down and refill, then calculate your actual MPG. Now enter test 20 to get the old Correction Factor.
NEW CF= OLD CF *(OBC MPG/Actual MPG)
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.