OJs Autobahn - Diagnostics connector

Diagnostics connector

Updated: Feb 2007

The diagnostics connector is found near the left front strut in the enginebay on inline 6's and V12's. On V8's it can be found on the right side of the engine bay.

Diagnostics connector (left with lid) shown to the left next to the two engine control connectors (V12 shown).

To open it, twist the lid counter-clockwise and lift up. The lid is actually a connector in itself, which shorts two different set of pins in the plug.

Lid shorts these pins. Seen from front of V12 engine/car.

All the blue pins are connected to eachother. The green ones also connect to eachother. These are the RxD and TxD bus pins (receive and transmit data) which are connected to ground and +B respectively when the lid is attached.

The bus connects to various devices in your vehicle, depending on model and manufacturing year. Usually it's connected to the alarm system, general module, heater controller, and seat/mirror memory units, to mention a few.

Pin description

Note! This applies to ALL E32 models without exception unless noted.

Seen from front of V12 engine bay/car. To the left is the engine inlet, and to the right one shock strut tower.

Pin	Description	Notes
1	Engine speed	provided by ignition coil or DME #1
2	N/C
3	N/C
4	N/C
5	N/C
6	N/C
7	Oil and Service Inspection reset input	Connects to inst.cluster X16 pin 16
8	N/C
9	N/C
10	N/C
11	Remote starter	Allows starter to be run by connecting to pin 14
12	Charging ok / Engine running	Alternator charging output
13	Vehicle speed	ONLY 91-93 750's
14	+B terminal	Always hot (12V)
15	RxD Data (receive)	Connected to vehicle accessories*
16	Start / Run (power from fuse 28 - 15A)	Hot when ignition in start or run position
17	N/C
18	DME data line	Connected to vehicles DME unit(s)*
19	Ground
20	TxD Data (transmit)	Connected to vehicle accessories*

*) databus lines. One for sending and one for receiving data. DME(s) have their dedicated own single send/receive databus line. Possibly for performing DME diagnostics and controlling other units at the same time, or to allow re-programming of the DME's while in-car.

Some basic functions can be performed:

Remote start or crank engine by connecting pin 11 and 14, for ie. compression test. To allow car to start the ignition must be in position II (run).
Programming and diagnostics can be performed by reading and sending data on pin 15 and 20. All connected devices in the vehicle can be access and reprogrammed this way. Also known as coding of devices.
Oil and SI indicators can be reset by performing the correct procedure by shorting pins 7 (Oil/SI reset input) to pin 19 (ground). See the SI-reset procedure article found on this site as well.
When the lid is attached it safely connects one dataline to ground and the other to +B via connectors in the lid. This is known as bus termination to avoid corruption of the datastream between the devices in the vehicle.

I intend to build an adapter to hook up my home computer to this diagnostics connector, and try and debug the information available. From this I hope to be able to read out error codes and more, since my car don´t have the Check Engine Light which can blink out error codes. This method is know as the Stomp Method. It can be performed on all US cars, and I've heard on no European cars. But I am working on a way for Europeans to hook up a lamp or LED to be able to get their errorcodes. Schematics will be posted on this site when I get it working. The Check Engine Light is connected to the instrument cluster by a grey wire on connector X502 pin 3. It activates the Check Engine Light by grounding.

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