Generating diagnostic trouble codes

WARNING: This page is about a different car, the 2001 Saab 9-3. However, it is still accessible from the selected car via links, so may be relevant.

Fuel Level, plausibility diagnosis: Because the fuel level is used as enable criteria in certain diagnoses, the control module must know that the fuel level value is plausible. The way it works is that the Trionic receives a bus message "Fuel level XX litres" from the MIU. During driving the Trionic observes the value and as the car is driven, fuel is consumed. The Trionic makes sure the fuel level value drops. In the Trionic a number of important filtrations are carried out to avoid faults caused by, for instance, splashing fuel in the tank, starting uphill. The fuel level diagnosis can be called a support diagnosis, it does not generate a DTC, but if for instance the EVAP tank pressure sensor diagnosis has reported performance problems (e.g. high value) in the EVAP tank pressure sensor then DTC P1453 is normally generated. If on the other hand the tank pressure sensor diagnosis has reported the same fault and the fuel level diagnosis has simultaneously reported a fault the DTC P1493 is generated instead.
Diagnostic trouble codes are generated when the fault criteria are fulfilled and the dependants are OK.