A method for detecting whether an injector with a valve controlled by a PWM signal of an SCR system is at least partially clogged, the system including a pump, or a positive-displacement pump, driven by a motor and pressure of which is controlled by a controller that continuously measures the pressure and/or another parameter characteristic of energy transmitted by the motor to the pump. According to the method, during normal operation of the SCR system, specific portions of one of the measurements are compared with equivalent portions stored in a memory.