# Description of OBC functions

The full OBC was standard on all 6 cylinder cars except 325iX, and optional on 318's. It was however, able to be deleted to reduce cost.

### Functions

| Actual time
| Date
| Stopwatch
| Average speed
| Speed limit warning
| Outside temperature
| Range on remaining fuel
| Average fuel consumption
| Immobilization of vehicle, including alarm.

Except for the car immobilization function (CODE), all functions can be displayed by means of the remote control button located on the end of the turn signal / high beam switch. When the knob on the turn signal switch is pressed, the various functions are selected consecutively in the same order as on the keyboard, beginning in the top left (time).

The selected function is displayed digitally with the relevant unit of measurement or designation on the right half of the LCD display

A numerical value input is made at the 1000, 100, 10 and 1 buttons in any desired order. Each time a button is pressed, the input value for the corresponding decimal place ( thousands, hundreds, tens or units) goes up by 1. When the figure 9 is reached, the display reverts to 0 on the next press of the button. If a button is held in, the value increases by 1 automatically every 0.5 second. The sequence of figures may be cut short for certain functions, such as Date.

Zeroes in front of a numerical input are not displayed.

To start the actual time and date displays accurately to the nearest second, press the contact next to the 1 button.

Light emitting diodes next to the speed limit and stop watch / timer provide an optical reminder of these functions being active.

To adapt the on board computer to suit various car and national market versions, there are two means of adjustment of the On Board Computer.

1. Coding plug for specific vehicle characteristics ( on rear of unit), number of cylinders, distance impulse counter, fuel consumption measurement characteristic, fuel injection, etc.
2. The national market function changes are obtained by pressing the changeover contact next to the 1 button.

The OBC system consists of the display unit and the following sensors

| Fuel consumption meter ( in instrument cluster)
| Fuel level sensor ( in fuel tank)
| Fuel reserve contact ( in fuel tank)
| Distance impulse transmitter ( in differential)
| Ambient temperature sensor ( in front spoiler)

Systems which the computer can control are the warning gong which sounds inside the car and the car immobilization system, which is operated by two relays, one for the ignition cutout and the other for the car's horn.

The On Board Computer is a single equipment block comprising of the LCD display, the keyboard, including two LEDs, the complete electronic circuitry, the coding plug and the contact for national market information selection.

To check which coding plug is installed without having to remove the OBC, press numerical input buttons 1 and 100 at the same time to display the identification number on the coding plug.

#### Vehicle

#### Fuel tank capacity

#### Reserve capacity

#### Display

#### Part number

318i (1984 - 1985) | 55 Liters | 6 Liters | 3-3 TYP | 65 81 1 376 027
325e (1984 - 1987) | 55 Liters | 6 Liters | 3-8 TYP | 65 81 1 373 698
325e (1988 -» ) | 65 Liters | 6 Liters | 4-4 TYP | 65 81 1 385 939
325i (1987) | 55 Liters | 6 Liters | 3-1.2 TYP | 65 81 1 381 793
325i (1988 -» ) | 65 Liters | 6 Liters | 4-6 TYP | 65 81 1 381 792
M3 | 55 Liters | 6 Liters | 3-1.1 TYP | 65 81 1 381 792

Whenever the OBC is reconnected to the car's power supply, an internal test routine takes place automatically. If a computer fault is detected, the display reads PPPP as a sign that the coding plug is defective or missing.

As a further stage in the test, the electronic analog-digital converter is checked. If it supplies an incorrect value, AAAA is displayed when one of the following functions is selected : Outside temperature, range, average fuel consumption.

The LCD display is divided into two display sections of different size. The function display uses an 8mm high LCD, whereas the LCD for the information or unit is only 6mm high.

When the ignition key is turned to position 1 or beyond, the display is back lit at all times. Its intensity varies with the other instruments when the rheostat is turned and the lights are on.

As a further function for calibrating the OBC after components have been renewed, the fuel tank contents can be displayed by pressing buttons 1 and 1000 simultaneously.

### Components

#### Temperature display

The outside temperature sensor of thermal conductor pattern, supplies a continuos signal representing the momentary temperature value. It has a resolution factor of 0.5° C. The display range extends from -22°F to +122° F ( -30° C to + 50° C)

#### Distance Impulse Transmitter

The distance covered by the car is measured with the aid of the electronic speedometer signal. Signal frequency is proportional to road speed.

#### Fuel Consumption Meter

The OBC can process and display average fuel consumption values. The electronic fuel injection control unit transmits a signal pulse for each injector operating cycle to the computer. There is a fixed relationship between pulse signal length and the volume of fuel injected.

#### Fuel Tank Contents / Signal

The signal form the reserve fuel contact and the volumetric resistor in the immersed fuel level sensor is supplied to the computer.

#### Miscellaneous

A language Integrated Circuit, with two additional language mode settings is used to ensure the correct units of measurement and function information for various countries.

The desired national market mode is obtained by pressing the changeover contact next to the 1 button after having selected AVG MPG and comes in sequence ( German USA UK, and repeats ) until the button is released.

The OBC reverts to German whenever there is a loss of power.

The Average Consumption and Average Speed functions are calculated for the distance the car has covered since the SET-RES button was last pressed during that display.

The Stopwatch function will continue to run even if the ignition is turned off.

The immobilization system takes effect only in ignition key position 3 , the engine will not start and the alarm is sounded after three attempts to start the engine have been made.

### Functions

#### HR-DATE (time/date)

The actual time and the date appear alternately each time the button is pressed. The date display takes no account of leap years.

The order in which the month and day are displayed varies according to the chosen national market mode.

If the HR function is selected, the changeover contact can be pressed in (e.g. with a ball point pen) and the four numerical input buttons then used to set the time. The clock function begins to operate when the contact is pressed in again. This can be carried out to within a second's accuracy by reference to a suitable time source or signal. To change from AM to PM or back if the display provides this information ( twelve hour clock) press the 1000 button. Each time the figures advance through the 0-1-2 sequence, a change takes place from AM to PM and so on.

The date is adjusted in the same was as the actual time display. This function is identified by the decimal points reappearing.

#### AVG MPH (average speed)

After SET-RES has been pressed, the calculated average speed is displayed when this function is selected. The calculation can be recommenced from zero for a further section of the journey after the ignition key has been turned to position 1 or further.

#### M MPH ( speed limit warning)

Display of the speed limit stored in the memory, visual and audible warning on pressing the button again after reaching the limit speed. The red LED comes on when the function is activated and flashes when the speed limit is exceeded. With the limit function selected, a new value can be superimposed over the old one. The stored value is not lost when he ignition is switched OFF

The warning gong sounds at the moment the speed limit is exceeded, but only if the difference between the selected limit and the car's actual speed at the moment, or since the last warning, exceeds or is equal to 3 mph (5 km/h)

#### RANGE

Display of the distance the car could still cover on the fuel remaining in the tank. If the float of the immersed fuel level indicator is still against its upper limit stop, a plus sign is displayed in front of the value. After refueling, no average value is calculated for a period of 4 minutes. Display of the new range takes place only after the ignition has been turned OFF and then ON again as far as position 2. The minimum fuel quantity which yields a range value is 1.3 gallons ( 5 liters)

#### TIMER ( elapsed time / stopwatch)

Stopwatch function when TIMER is selected, the display shows the increasing time or the last stopped time. The stopwatch is set in motion by pressing SET-RES. The same button is pressed again to halt the stopwatch.

#### TEMP (outside temperature)

When this key is pressed, the temperature outside the car is displayed. There is an audible and visual warning (with the OBC automatically switched over if other functions have been selected) as soon as a temperature of 37.5° F (3° C) or below is reached, the gong sounds and the unit of measurement display flashes when the on board computer is switched on.

The audible warning sounds again if the lower limit is reached after the temperature has risen in the meantime to 43°F (6°C), or if the limit has been reached for the first time since the OBC was restarted.

#### CODE ( Car immobilization / alarm )

Input of a numerical code with the ignition key in position 1 is followed by memorizing of the code when the ignition key is turned back to position 0

The code function is indicated at ignition key positions 1 and 2 by the CODE display and segments of the numerical display flashing. The correct code must then be supplied to the system. After three incorrect entries or a starting attempt, the alarm is sounded at the additional horn. If the code input is correct, it is evaluated by the computer and can be finally accepted by pressing the SET-RES key or by starting the engine. Any combination of figures including 0000 can be used as the code.

#### SET-RES (start /stop)

This is the start button when calculating average speed, average fuel consumption or restarting the stopwatch. After input of a numerical code, this button is also used to cancel the immobilization system when the correct code has been supplied by the driver.

#### 1000, 100, 10 , 1

Buttons for the input of numerical values in any desired order, after pressing the appropriate function button ( HR-DATE, M MPH, TIMER or CODE)

E30 M3 Repair Manual V2.7. Copyright ©1999-2001 Koala Motorsport & Brett Anderson