The invention relates to a method for controlling a low-voltage-powered plug (2) for preheating a diesel engine (1) air/fuel mixture. The plug (2) is powered by pulses having a predetermined amplitude and duration, said amplitude being less than a maximum amplitude (PWM_MAX). The amplitude and duration of the voltage pulses powering the plug (2) are controlled as a function of first parameters including the duration of the preceding pulses and the duration between successive preceding pulses.