Toyota Prius Owners Manual
Emissions inspection and maintenance (I/M) programsVehicle maintenance and care / Emissions inspection and maintenance (I/M) programs
Some states have vehicle emission inspectionprograms which include OBD(On−Board Diagnostics) checks.
The OBD system monitors the operationof the emission control system. When theOBD system determines that a problemexists somewhere in the emission controlsystem, the malfunction indicator lampcomes on. In this case, your vehicle maynot pass the I/M test and need to berepaired. Contact your Toyota dealer toservice the vehicle.
Even if the malfunction indicator lampdoes not come on, your vehicle may notpass the I/M test as readiness codeshave not been set in the OBD system.
Readiness codes are automatically setduring ordinary driving. However, when thebattery is disconnected or run down, thecodes are erased. Also, depending onyour driving habits, the codes may not becompletely set.
Also, if the malfunction indicator lamp hadcome on recently due to temporary malfunctionsuch as a loose fuel tank cap,your vehicle may not pass the I/M test.
The malfunction indicator lamp will go offafter taking several driving trips, but theerror code in the OBD system will not becleared unless about 40 trips or more aretaken.
If your vehicle does not pass the I/M testand the malfunction indicator lamp doesnot come on, contact your Toyota dealerto prepare the vehicle for re−testing.