To prevent damage or excessive wear on the fiction units in the automatic transmission, the ignition ecu (EZK and possibly EZF as well) have a feature to take away part of the engine torque while switching gears by retarding the ignition timing. This reduces slipping in the clutches of the transmission. To do this a pressure operated switch is installed in the transmission and when a gear change takes place it connects so that the ignition ecu knows that it should retard ignition timing.

Stepping gear up: 350ms delay, retarding ignition 16 degrees
Stepping gear up: 50ms delay, retarding ignition 16 degrees
 

There is another feature that retards timing. The S4, GT and GTS have a hall sender and knock sensors. To adjust timing as best as possible, the EZK monitors knocking on the engine (uncontrolled and unwanted pre-detonation) using the knock sensors. To know which cylinder is doing the knock (and needs adjusting) it needs to know in which part of teh 4stroke cycle the engine is in. The Hall sender at the back of the passenger side (LHD) cam wheel senses this and tells the EZK. However.... if teh EZK fails to see the Hall sender signal, it is unsure what to do and adjusts on the safe side....

When the hall sender is failing to send a signal, the ignition timing is retarded 6 degrees