A system and method for selecting the data content of an ionization feedback signal is disclosed. An ignition system monitors both the ionization signal and ignition coil dwell data. The ignition system outputs either the ionization signal or the ignition coil dwell data on the ionization feedback line, depending on what information is desired by the powertrain control module. In one embodiment, the ionization signal is only output during the before ignition period when the operating condition of the engine indicates possible pre-ignition conditions.