Diagnostic Overview
WARNING: This page does not describe the selected car, but rather 10 other vehicles, including the 2010 BMW M6, 2010 BMW M5, 2009 BMW M6, 2009 BMW M5, and 2008 BMW M6. However, it is still accessible from the selected car via links, so may be relevant.
The rationality check of the system is divided into two sections.
Firstly, the engine-control-unit (ECU) stores the relative time information when the engine is stopped. At restart the difference to the current relative time is used to evaluate the time, the engine has been off. This engine-off-time is checked against the dropping time of engine coolant temperature (ECT)
Secondly, the independent timer of the ECU is compared to the relative time measurement to see if they are synchronized.