90 fault codes

["Lebens, Rick J" <M245884@flt-test-02.mdc.com>]

I drive a 1991 Audi 90 Quattro.  Recently I have experienced some cold start 
problems.  Wanting to start with the simple things I wanted to check for self 
test faults.

Reading the Bentley manual for this car I have concluded that there is no check
engine light to warn of self detected faults.  The manual also differentiates 
between pre and post March 1990 production.  Mine being a post March 1990 
production model.  The Bentley manual does not have a procedure for retrieving 
fault codes from this model without using the VAG 1551 tester.

Of the three connectors under the dash (black, brown and blue) one is labeled 
blink code output but the pin out is different from earlier models.  Does anyone 
know how?

On the side does anyone know the signal levels and protocol of the bi directional 
serial data.  It would sure be neat to build a level shifter or 
whatever and plug it into my RS-232 port.


                                                             Thanks   
                                                              RickL