Power Source Mode does not Change: Description
WARNING: This page is about a different car, the 2006 Lexus IS 250. However, it is still accessible from the selected car via links, so may be relevant.
If the certification ECU detects the key inside the vehicle when the shift lever position is P (A/T) and the brake pedal (A/T) or the clutch pedal (M/T) is not depressed, each press of the engine switch changes the power source mode in the following order: off, on (ACC), on (IG), off. If one of the DTCs shown in Figure is detected, correct the DTCs according to the DIAGNOSTIC TROUBLE CODE TABLE . If the power source mode is still malfunctioning, one of the following may have occurred: 1) the MPX circuit has a malfunction, 2) the certification ECU has determined that the electrical key is not inside the vehicle, 3) the engine switch has a malfunction, or 4) the power source control ECU has a malfunction.