Trionic is an engine management system developed by Saab Automobile.
'Ion' comes from the fact that it uses ion current, measured by the spark plugs between combustion events which acts as a sensor for knock, misfire and synchronization detection.
Using the value and wave shape of the current, after the actual spark event, the quality of the actual combustion process is determined, thus allowing the engine control unit to optimize the timing of the spark for the best engine performance while keeping emissions low on a much wider range of rpms.
The Trionic 5.2 and 5.5 systems utilized the manifold absolute pressure (MAP) sensor and the intake air charge temperature sensor to calculate the fuel injection curves, while the Trionic 7 and 8 systems are mass air flow type.
optional on 00-02 four cylinder models Trionic systems are shortened to indicate their version; for e.g. T5, T7, T8, etc.