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2010 Forester XT
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75 Posts
Discussion Starter #1
I'm sure this is a stupid question, but I can't find a straightforward answer.

Consider the following:

1. I take my stock ecu tuning map, and use an accessport or opensource cable to save a copy.
2. I then flash a different map to the ECU.
3. Later I overwrite the ecu with the original map.

Does the programming then look the same as it does "stock"? Can somebody else (dealer) tell changes have been made?

Does the answer to the above change if I use an accessport vs. opensource?

I am asking the question not out of some nefarious plot to make Subaru pay for my fun in modding my engine in irresponsible ways, but more because it may play a role in whether I decide to do ANYTHING to the ECU under warranty.

As I mentioned in a previous post, I live in Colorado, and many times stock tunes are just not up to snuff considering the altitude. When I have messed with ECU tuning in the past, I have also liked to change innocuous stuff like the coolant temp that the fans turn on and the like.

I would hate to lose warranty coverage because I messed around with fan turn on, and the dealer sees that the ecu has been modified and thus I have no warranty.
 

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8,844 Posts
Yep, it shows that it has been rewritten even when the dealer does a reflash. However they would have to show that what you did caused the problem for them to deny warranty coverage.
 

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2007 Sports XT 4EAT (former)
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2,485 Posts
If they look hard enough they can figure it out, yes. The ECU has a checksum that will show if it has been altered in any way. Whether they dig that far or not would be the question, and probably depends on dealer and the type of warranty claim.
 

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Premium Member
2009 Outback XT-B 5MT
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10,254 Posts
Yes and no, actually.

There is a check-sum that changes anytime the ROM changes. The trick is that the ROM changes even if a dealer turns on a "port delivery" feature (such as eliminating the time-out for the rear defroster). So they can tell if a ROM has changed, but I don't believe it goes as far as reporting changes.

On the newer cars, like the 2010 Legacy and Outbacks, there is a lot more that can be "seen". A whole boat load of info can be logged.

The version 3 AP's copy the stock ROM directly, then when unmarried, will reinstall that ROM as if it were never flashed.
 

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05 Forester XT
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541 Posts
So if you have a Cobb stage 1 map, what's the right way to prevent the dealer from screwing around with the map (and bricking your AP)
I assume there isn't any map upgrade being done to a 2005, so what are the chances they would do a remap at say the 60k service?
 

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Premium Member
2009 Outback XT-B 5MT
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10,254 Posts
I think standard practice is to unmarry your AP any time you take the car in to the dealer. That way, if an ambitious tech decides to update your ECU as a courtesy, he won't cost you a bunch of money.
 

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2010 Forester XT
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75 Posts
Discussion Starter #7
The version 3 AP's copy the stock ROM directly, then when unmarried, will reinstall that ROM as if it were never flashed.
Does this still mean the checksum is different?

And I take it from the responses that even if the checksum is different, there is not a corresponding timestamp, or some way to tell how many times it has been flashed?
 

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Premium Member
2009 Outback XT-B 5MT
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10,254 Posts
I think the checksum WILL change, but there is no time-stamp and I believe a whole bunch of looking is required to KNOW that the checksum has changed.

I'm not 100% positive on this, but I don't know if the ECU differentiates between a total reflash (like a stage-1 flash) and a mere changing of a simple parameter contained within the ecu (like the defroster thing).
 

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Premium Member
2017 VW Golf SportWagen 5MT
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10,784 Posts
I just assume the dealership would know that I've flashed the car, I'm almost 100% sure they would. You could email COBB to see what they say on the subject. Same with the open-source tools -- I'd ask whomever writes the tools. But, from everything I've read, the dealership has the capability to see if the ECU's been flashed.

Stan
 

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Administrator
2007 Forester Sports XT 4EAT
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39,434 Posts
This is from the COBB website, in the AccessPORT FAQ. :wink:

Bobby...

Q. Can a dealer detect that I have an AccessPORT installed?

A. Yes, this is possible unless you use the [Revert to Stock] menu option to load a purely stock program on the ECU. While the vehicle can be serviced by the dealership in the same way as a stock vehicle, and all the Dealer scan tools function 100% the same, the data on the ECU has a marker known as a "checksum". Whenever any data on the ECU is changed, this checksum value must be changed in order for the ECU to operate. If a dealership compares this checksum value against another stock car, the values will be different. If you use the [Revert to Stock] menu option to uninstall the AccessPORT from your vehicle, the checksum on the ECU is now a valid stock checksum. No markers are left by the AccessPORT when using the [Revert to Stock] menu option.

['07 FSXT MODding Journal] ['03 X MODding Journal]
 

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2010 Forester XT
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Discussion Starter #11
This is from the COBB website, in the AccessPORT FAQ. :wink:

Bobby...

Q. Can a dealer detect that I have an AccessPORT installed?

A. Yes, this is possible unless you use the [Revert to Stock] menu option to load a purely stock program on the ECU. While the vehicle can be serviced by the dealership in the same way as a stock vehicle, and all the Dealer scan tools function 100% the same, the data on the ECU has a marker known as a "checksum". Whenever any data on the ECU is changed, this checksum value must be changed in order for the ECU to operate. If a dealership compares this checksum value against another stock car, the values will be different. If you use the [Revert to Stock] menu option to uninstall the AccessPORT from your vehicle, the checksum on the ECU is now a valid stock checksum. No markers are left by the AccessPORT when using the [Revert to Stock] menu option.

['07 FSXT MODding Journal] ['03 X MODding Journal]
Good to know.

With opensource options, when you reflash a stock tune, will the checksum again look stock?

If not, this is a good reason IMO to use an AP.

Thanks for the info, guys.
 
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