Diamond DA 40 Flight Manual page 251

Airplane
DA 40 AFM
Description
7.9.4 ENGINE INSTRUMENTS
Button 1: Lean mode
Button 2: Digital exhaust gas / cylinder head temperature mode
Button 3: Switch in autotrack
Button 4: Fuel computer mode
Button 5: Engine data recorder
Button 3 has an additional function on switch-on: Display mode
Doc. # 6.01.01-E Rev. 8 01-Dec-2010 Page 7 - 25