This isn't strictly mirco related but I figured one of you guys should know *something*

My brother recently bought a 1999 alfa 156 and after some Mass Air Flow sensor trouble (fixed now) he decided that *I* should figure out how to plug his computer into the car for diagnostic info.

As far as i have found out the obd standard is pretty well established and supports multiple communication protocols. i think the alfa uses OSI standard which requires an ELM232 chip to perform some data conversion and a cable from standard rs232 to j1962.

If anyone has done this sort of thing before (not necessarily for an alfa, i just put that in 'cos EVERYONE loves alfa) please help

Thanks

You are working in very interesting area...

Are you sure about OSI standard ...not ISO standard?
http://www.obdii.com/obdii.html

OBD-II Signal Protocols

There are five protocols in use with the OBD-II interface, and often it is possible to make an educated guess about the protocol in use based on which pins are present on the J1962 connector:


* SAE J1850 PWM (41.6 kbaud, standard of the Ford Motor Company)
o pin 2: Bus-
o pin 10: Bus+
o High voltage is +5V
o Message length is restricted to 12 bytes, including CRC
o Employs a multi-master arbitration scheme called 'Carrier Sense Multiple Access with Non-Destructive Arbitration' (CSMA/NDA)

* SAE J1850 VPW (Variable Pulse Width) (10.4/41.6 kbaud, standard of General Motors)
o pin 2: Bus+
o Bus idles low
o High voltage is +7V
o Decision point is +3.5V
o Message length is restricted to 12 bytes, including CRC
o Employs CSMA/NDA

* ISO 9141-2. This protocol has a data rate of 10.4 kbaud, and is similar to RS-232. ISO 9141-2 is primarily used in Chrysler, European, and Asian vehicles.
o pin 7: K-line
o pin 15: L-line (optional)
o UART signaling (though not RS-232 voltage levels)
o K-line idles high
o High voltage is Vbatt
o Message length is restricted to 12 bytes, including CRC

* ISO 14230 KWP2000 (Keyword Protocol 2000)
o pin 7: K-line
o pin 15: L-line (optional)
o Physical layer identical to ISO 9141-2
o Data rate 1.2 to 10.4 kbaud
o Message may contain up to 255 bytes in the data field

* ISO 15765 CAN (250kbit/sec or 500kbit/sec)
o pin 6: CAN High
o pin 14: CAN Low

Note: Pins 4 (battery ground) and 16 (battery positive) are present in all configurations. Also, ISO 9141 and ISO 14230 use the same pinout, thus you cannot distinguish between the two simply by examining the connector.