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Old 05-07-2012, 07:28 PM   #21
nightdown fox
Scooby Specialist
Member#: 309636
Join Date: Feb 2012
Chapter/Region: MAIC
Location: Baltimore, MD
2015 STI LE
WRB on Gold!


Here's an email from Christian at COBB from 2006 that I found...

Since 2002, Subaru ECU's with OBD2 have the ability to report their CID
values. In 2005, Subaru added CVN and VIN reporting as well. What does
this all mean?

*CID stands for Calibration Identification Number. *
The CID is basically the software version number for the software and
calibration data stored on the ECU. We've basically referred to this by
using the ECU part number for simplicity. For example, a 2002 WRX with
an ECU part number 22611AF424 we've referred to as "AF424". This is
also what we've called the "ECU Identifier" in our Map Manager
software. In reality, the actual CID value does not match in any way
the part number displayed on the case. We simply use the part numbers
as its easier for the end user. Any OBD-II scanner should have the
ability to poll the ECU for this value, as well as the Subaru Select
Monitor II and the newest Subaru Select Monitor III. When the
AccessPORT is installed, or uninstalled, the CID reported is always a
valid Subaru version number for that vehicle.

*CVN stands for Calibration Verification Number. *
The CVN is basically a "check sum" of the data stored on the ECU. This
is used to determine if the data on the ECU has been corrupted or
changed. If someone is to change the data, like we do when the
AccessPORT is installed, the reported CVN will be different than
normal. Any OBD-II Scanner can return the CVN from an ECU that supports
this function. The Subaru Select Monitor II and III can also read this
data. The big difference between the SSM II and III now is the reported
ability for the SSM III to tell the technician if the CVN is valid for
the CID or not. Basically, does the Check Sum value match what it
should be for that version of ECU software. Remember, the CVN will
change with each software revision. If a technician were to check for
this manually, like they would when using the SSM II or any OBD-II
scanner, they would have to know what the CVN should be for each given
software revision (CID) for each vehicle. That represents around 200+
possible combinations for Subarus sold in the USA since 2002. Not very
likely to be memorized, but it is possible the SSM III could store this
data for the technician and check automatically. That's not proven,
just a known possibility given readily available technology.
When the AccessPORT is installed, it changes the CVN so it no longer
matches the valid value for the CID. This is required because we are
altering data in the ECU. If the CVN is not correct for the new data,
the ECU will fail its internal check and not run because it thinks it
data is bad. So, we are forced to alter the CVN if we want the ECU to
run with the new data. That means we're not changing the CVN for the
sake of changing it, we have to in order for the ECU to operate.
When the AccessPORT is uninstalled (Reverted to stock), the CVN
_*matches*_ the CID.

*VIN stands for Vehicle Identification Number.
*The VIN is a unique number given to each vehicle sold. This data is
not currently stored on the ECU, and it not something we alter or change
in any way. This was added by Subaru on 2005 models. If you change the
ECU in these cars to another vehicle, it will not alter the VIN.

*Subaru Select Monitor III
*The new Subaru Select Monitor (III/3/Three) is a PC based system just
released in the past few months to dealers only. We have had dealers
testing the new SSM-III on vehicles with AccessPORTs installed and there
is no compatibility issues. Normal diagnosis, etc can be performed. However, due to the fact that the new SSM-III is software based, it will
be easy and quite plausible for Subaru to change its function in the
field as necessary. Thus, its functionality will always be evolving.

If a current or potential AccessPORT user is concerned about their
vehicle's compatibility with the new SSM-III, it is advised they Revert
To Stock before any dealer visits. In this instance, all ECU data will
be stock and there should never be any compatibility issues, current or

The new SSM-III also gives the dealership the ability to reprogram the
ECUs at will. In the event this is done to perform an update and the
customer has not uninstalled their AccessPORT, the special "key" stored
on the ECU that lets their particular AccessPORT work on their ECU will
be erased by the SSM-III reflash. In this event, the AccessPORT will no
longer work with their ECU or any other ECU until returned for service.

Finally, there is no evidence that Subaru ECUs or tools have the ability
to determine how many reflashes of the ECU have occurred. There is no
known counter mechanism employed, nor any evidence that such a system
sits in-line with the ECU to capture this data. The reflash process is
very sensitive already, it would seem a recipe for disaster to try and
employ additional complexity.

Hope that helps...and thank Trey for this clarification. I am just cutting and pasting

Take care,
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nightdown fox is offline   Reply With Quote