Playing with the ECM

[SRavet at bangate.compaq.com]

ws6transam at voyager.net (Daniel R Burk) Wrote:
| 
| >
| >Markus Strobl <eusmsrt at exu.ericsson.se> has written:
| >
| ><snip>
| >
| >> Second subject: I own a '96 Camaro with the LT1. The service manual I
| >> read was for a friends '95. GM did alot of changes for '96 to 
| >> comply with OBDII. My owners manual says that the ECM now detects
| >> misfires, and will flash the service engine light if it detects a
| >> misfire. The '96 also has 4 (!) O2 sensors (dual cat), to detect
| >> catcon degradation. 
| >
| >> Does anyone have any info on OBDII? Ie how much can the engine be
| >> modified before the ECM tilts? Can the ECM be modified, or can
| >> it be fooled be changing the sensor readings? Any info appreciated.
| >
| ><snip>
| 
| Marcus:  Before you modify your ECM let me tell you about a little 
conversation
| I have had with a GM engineer who actually worked in ECM design.
| 
| GM will be designing their new vcm (vehicle control module) with 
anti-tampering
| software.  There are three levels of information available on the new 
vcm:
|         1) general engine diagnostics (freely available to scan tools)
|         2) dealership functions (like clearing the trouble codes)
|         3) emissions functions ( fuel maps, shift maps, ignition timing)
| 
| As you can guess, level two will be only available to authorized service
| personnel.  Level three will be protected from modifications from 
everyone
| except GM.  
| 
| If someone like me, or you, or Hypertech, tries to gain access and change 
level
| three type of information in the new '97 VCM, and does not have the 
correct
| access code the FIRST TIME, the VCM will lock itself down into a
| non-functional unit that cannot be restarted except by engineers at 
Delco!!
| 
| Yup, it sucks don't it?  
| 
| I asked the engineer "Why!?"  and he replied it is because of liability
| concerns that GM is implementing this type of security.  
| 
| --- Thought you would like to know that I am going to buy me a used '95 
or '96
| in a few years.  I don't want the '97 anymore.
| 
| ---Dan
|  
| 
| 

I'd be interested in hearing that conversation.  The EPA published a rule 
in the Federal Register Aug 9 1995 that basically deals with what 
information has to be on the OBD bus.  Anything emissions related must be 
present and compliant with OBD-II specs so that any generic scan tool can 
read it.  In addition, *any* information relating to the diagnosis or 
repair of OBD systems that is available to dealers must also be made 
available to the general public.  Finally, manufacturers must have 
provisions for reprogramming ECMs in the interest of emissions related 
repair.  Since dealers have to know how to reprogram ECMs, the 
manufacturers will have to make that info available to everyone else.  The 
catch is, they can make it available "indirectly", in the form of a device 
that does the reprogramming, without telling people how it's actually done.

This conversation happened just this week somewhere else (on the efi332 
list?) so sorry if this is a repeat...

The bottom line is, keeping independant shops (and owners) from being able 
to repair their own cars is anti-competitive behavior.

Steve Ravet
sravet at bangate.compaq.com
Baby you're a genius when it comes to cooking up some chili sauce...