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Good explanations here. Let me try to dumb it down. Think about the ECU as the cars brain that tells the other parts and engine what to do, such as fuel mix. The ECU is a computer programmed with BMW's settings for telling the engine and components how to run. An ECU flash tune over writes BMWs settings with settings that are more aggressive and increase performance. The history of how the car runs from that point are stored in the DME and ECU, so BMW knows they were altered.
A piggy back has its own "computer" and setting that alters the commands outputted by the ECU after it sends the instructions. It's plugged into various modules and changes the instructions for the modules. It's so downstream, nothing is logged.
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2018 M550ix|Carbon Black|Dinan Modifications|2003 540i|Jet Black|M-Sport|2021 X5 Mineral White
Prior BMW's: 1987 325e|1993 740i|1998 740il|2001 530i|2002 745li|2007 750li|2006 750li|2001 530i|2012 535xi|
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