Modifying OBD-II systems

[Donald Whisnant]

> 
> Date: Thu, 13 May 1999 20:36:14 -0400
> From: Todd Israels <israels at MNSi.Net>
> Subject: Re: Modifying OBD-II systems
> 
>         Without causing any trouble is it possible to read the current VE table
> and replace values in the table through the ADL interface?  From what I
> have heard from dealer tecs a new VE table or even operational program for
> the PCM but they are unaware of being able to read this info, but then they
> dont need to?
>         thanks for any info you can give        
>                                                 Todd Israels
> 

Todd...

Anything is possible via the ADL port -- actually called the DLC port on
newer vehicles...  Reading is actually easier than writing...  Since the
PCM uses flash memory, you can't write without erasing (unless you are
only changing a '1' to a '0')...  That means the write code must also
know how to erase the flash and the read doesn't and is thus inherently
more complex...  Also, it means that most "writes" can NOT occur "on the
fly" with the vehicle running -- since erasing the flash will kill it,
not to mention screwing up checksums...

Thats about all I'm allowed to say...
Donald