[Gmecm] OBD2 reflashing

[Steve Ravet]

This is something I sent offlist to someone who asked.  I thought people
on the list might find it interesting.  It's a capture of the very
beginning of a reflash sequence on the OBD2 bus.  It doesn't include any
actual data, but the seed/key is there, and requesting the faster 4X
J1850 mode is there.  If you don't already "speak" J1850, then take a
look at the Intel whitepaper on the gmecm page.  ECM info, OBD2 info,
Intel whitepaper.

--steve

6C	FE	F1	3F			
Tester present message from scan tool to PCM.  repeats periodically.


6C	10	F1	27	1		
scan tool requests seed from pcm

6C	F1	10	67	1	71	42
pcm responds with seed 7142.  If the PCM was already unlocked it would
be 0000

6C	10	F1	27	2	44	B9
scan tool responds with key 44b9

6C	F1	10	67	2	34	
not sure

6C	FE	F1	28	0		
scan tool request to disable normal messages (sensor data that is
broadcast regularly, such as VCC)

6C	F1	10	68	0		
PCM says OK

6C	FE	F1	3F			
scan tool present

6C	FE	F1	A0			
scan tool request high speed mode

6C	F1	10	E0	AA		
PCM says OK

6C	FE	F1	3F			
scan tool present

6C	FE	F1	A1			 
scan tool begin high speed mode.


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