An injector is configured to receive therein a cartridge containing a substance to be dispensed. The injector includes an injector housing and an injector door movably mounted to the injector housing between a fully closed position and a fully open position. The injector door is initially locked in an at least partially closed position preventing insertion of the cartridge into the injector. The injector further includes a controller configured to conduct an initial self-test on operability of at least one component of the injector. The self-test has a single pass or fail outcome, wherein the injector door is unlocked and enabled to be moved into the fully open position, to enable insertion of the cartridge into the injector, solely upon achievement of the self-test pass outcome.